Asterion: The Practical Handbook of Anatomy Harishanker JS, Ajai Sasi, Avinash N
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HistologyCHAPTER 1

2
 
Epithelia
 
SIMPLE SQUAMOUS EPITHELIUM
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SIMPLE CUBOIDAL EPITHELIUM
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3
 
SIMPLE COLUMNAR EPITHELIUM
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CILIATED COLUMNAR EPITHELIUM WITH GOBLET CELLS
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PSEUDOSTRATIFIED COLUMNAR EPITHELIUM
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TRANSITIONAL EPITHELIUM
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Cartilage
 
 
General Aspects
  • Develops from primitive mesenchyme.
  • Three types:
    1. Hyaline
    2. Elastic, and
    3. Fibrocartilage
  • It consists of cells viz. chondrocytes, chondroblasts, fibroblasts, connective tissue fibers and ground substance.
  • The ground substance of cartilage is made of proteins and carbohydrates, they form a meshwork which is filled by water and dissolved salts.
  • Nonvascular, nutrition via diffusion. However researches have shown the presence of cartilage canals through which blood vessesls may enter the cartilage.
  • The highly hydrated nature of ground substances is responsible for diffusion.
 
Structure
  • Matrix with chondrocytes surrounded by perichondrium (except in fibrocartilage, and hyaline cartilage at articular surfaces).
  • Matrix consist of connective tissue fibers.
  • Cells in the matrix exist in lacunae (singly or in isogenous groups).
  • The nucleus of cartilage cells are initially euchromatic, as cells starts to mature the nuclei become heterochromatic.
  • Perichondrium consists of two layers:
    1. Outer fibrous layer made of type 1 collagen fibers.
    2. Inner cellular/chondrogenic layer contains chondroblast cells.
  • Growing pattern are by two different ways:
    1. Interstitial growth: Newly formed cartilage grows by proliferation of cells throughout its substance.
    2. Appositional growth: It occurs in mature cartilage. Growth of cartilage takes place by addition of new cartilage over the surface of existing cartilage.
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HYALINE CARTILAGE
  • Perichondrium is present.
  • Chondrocytes are present inside the lacunae and are arranged homogenously in the matrix.
  • In hematoxylin and eosin staining, the matrix is basophilic (i.e. stained blue in color).
  • Chondrocytes in the center are larger than those at periphery.
  • Matrix can be differentiated into two types:
    1. Territorial matrix: Darker matrix adjacent to chondrocytes.
    2. Interterritorial matrix: Lightly stained matrix between chondrocytes.
  • Ground substance consists of type 2 collagen fibers.
  • For example, costal cartilage, trachea, thyroid cartilage.
 
Applied Anatomy
  • Hyaline cartilage forms the skeleton of the fetus. The cartilage forms a framework of the bones and later endochondral ossification occurs and is replaced by bone.
  • Hyaline cartilage calcifies on ageing whereas elastic cartilage does not.
  • Chondromas are benign tumors of cartilage, in which the chondrocytes are arranged in clusters with abundant intercellular stroma.
 
Viva-voce
Q. Costal cartilage is composed of what type of cartilage?
Ans. Hyaline cartilage.
Q. Which is the most abundant type of cartilage in the body?
Ans. Hyaline cartilage.
Q. Which type of cartilage forms the articular surface on bones?
Ans. Hyaline cartilage.
7
 
HYALINE CARTILAGE
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  • Cell nests of chondrocytes present.
  • Territorial and interterritorial matrix present, perichondrium present.
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ELASTIC CARTILAGE
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  • Large singly arranged chondrocytes in lacunae.
  • Perichondrium present.
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ELASTIC CARTILAGE
  • It is also known as yellow fibrocartilage.
  • Perichondrium is present.
  • Highly flexible.
  • Matrix contains numerous elastic fibers instead of collagen fibers.
  • Chondrocytes are larger, singly arranged and are present in lacunae.
  • In H and E staining the fibers are not clearly visualized, it is better seen in special staining methods like Verhoeff's method.
  • Density of fibers vary according to the site where it is present.
  • For example, external ear, epiglottis, auditory tube, etc.
 
Applied Anatomy
  • Elastic cartilage does not calcify on aging.
  • Due to its high flexibility it regains its shape quickly after being deformed.
 
Viva-voce
Q. What stain would be best to demonstrate the elastic fibers in elastic cartilage?
Ans. Resorcin-fuchsin and orcein would best show the elastic fibers in elastic cartilage.
Q. If you bend your ear forward, it bounces back into its proper position. Why is it so?
Ans. If you bend your ear forward, it bounces back into its proper position. This is due to the elastic cartilage present in the external ear. Due to its high flexibility it regains its shape quickly after being deformed.10
 
FIBROCARTILAGE
  • It is also known as white fibrocartilage.
  • It consists of alternating layers of cartilage matrix and thick dense layers of type 1 collagen fibers.
  • Collagen fibers are arranged as wavy bundles.
  • Chondrocytes in lacunae distributed in rows.
  • Chondrocytes are of similar size.
  • Perichondrium absent, since fibrocartilage form a transitional area between hyaline cartilage and tendon/ligament.
  • For example, intervertebral discs, glenoid labrum, symphysis pubis.
 
Applied Anatomy
It possess great tensile strength and considerable amount of elasticity.
 
Viva-voce
Q. Which type of cartilage forms the intervertebral disc?
Ans. Fibrocartilage forms the intervertebral disc.
Q. How is collagen fibers arranged?
Ans. Collagen fibers are arranged as wavy bundles.
Q. Which type of collagen fibers make up the fibrocartilage?
Ans. Type 1 collagen fibers.11
 
FIBROCARTILAGE
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  • Chondrocytes of similar size present between collagen bundles.
  • Perichondrium absent.
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COMPACT BONE: TRANSVERSE SECTION
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  • Presence of osteocytes in lacunae.
  • Haversian system present with concentric lamellae.
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Bone
 
 
General Aspects
  • Special form of connective tissue.
  • Bone formation occur by two processes.
    1. Endochondral ossification: Bone development is preceded by cartilage model.
    2. Intramembranous ossification: Bone develops from a connective tissue mesenchyme.
  • Bone types—compact and Spongy bone.
  • Bone contains cells, fibers (type 1 collagen fibers) and extracellular matrix.
  • There are four types of bone cells—osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts.
  • Bone matrix is calcified, and is harder than cartilage but contains living cells and extracellular materials.
  • Highly vascularized.
 
BONE TRANSVERSE SECTION
  • Haversian systems or osteons are the structural units of bone matrix.
  • Each osteon is outlined by a cement line.
  • Osteons are located between internal and external circumferential lamellae.
  • It consists layers of concentric lamellae arranged around a central canal.
  • Central canal consists of blood vessels, nerves and reticular connective tissue.
  • Lamellae contains osteocytes in spaces called lacunae and tiny canals radiate from lacunae known as canaliculi.
  • Small irregular areas of bone are present between osteons, known as interstitial lamellae and represents remnants of eroded osteons.
  • External wall is formed by external circumferential lamellae and internal wall by internal circumferential lamellae.14
 
BONE LONGITUDINAL SECTION
  • Osteocytes present.
  • Central canal is surrounded by lamellae with lacunae and canaliculi.
  • Volkmann's canal (perforating canal) is visible in longitudinal section (LS).
  • Volkmann's canal is formed by anastomoses between central canals.
  • Volkmann's canal joins the central canal with marrow cavity.
  • Concentric lamellae is absent in Volkmann's canal since they directly penetrate via lamellae.
  • Throughout life there is continuous destruction and rebuilding of haversian system.
 
Applied Anatomy
  • Inflammation of bone marrow is known as osteomyelitis.
  • Ischemia results in avascular necrosis of bones which is mainly caused by fracture or dislocation.
  • Osteoporosis is a condition resulted from the quantitative reduction of the normal bone.
  • Osteomalacia and rickets are conditions occurring in adults and children respectively characterized by qualitative abnormality as impaired bone mineralization due to deficiency of vitamin D.
  • Aneurysmal bone cyst is a expanding osteolytic lesion filled with blood.
  • Osteoarthritis is a chronic disorder of synovial joints characterized by progressive degenerative changes in articular cartilage over years.
 
Viva-voce
Q. What structures are found within haversian canals?
Ans. Capillaries and nerves.
Q. Is the osseous lamella adjacent to the haversian canal the youngest or the oldest lamella of a particular osteon?
Ans. The youngest.
Q. What structure in mature bone is created by the zone of resorption?
Ans. The marrow canal.
Q. What are the differences between intramembranous ossification and endochondral ossification?
Ans. Intramembranous ossification: Does not use a cartilage framework, bone develops directly on or within mesenchyme. Bone growth is appositional. Found in irregular bones such as the bones of the skull.
Endochondral ossification: Replaces a pre-existing cartilage framework. The bone lengthens through interstitial growth and changes diameter through appositional growth. Found in long bones.15
 
COMPACT BONE : LONGITUDINAL SECTION
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  • Osteocytes present.
  • Longitudinal section of haversian system and Volkmann's canal seen.
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SKELETAL MUSCLE
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  • Cylindrical muscle fibers with prominent striations.
  • Presence of peripherally arranged flattened multinuclei.
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Muscle
 
 
General Aspects
  • Types:
    • Skeletal muscle
    • Smooth muscle
    • Cardiac muscle
  • Muscle tissue consists of elongated cells called myocytes.
  • Muscle cytoplasm—sarcoplasm.
  • Cell membrane—sarcolemma.
  • Muscle fibers contains myofibrils.
  • Myofibrils made of contractile proteins called actin and myosin.
 
SKELETAL MUSCLE
  • Also known as voluntary muscle.
  • Muscle fibers are long, cylindrical and multi-nucleated.
  • Nuclei arranged at periphery and are elongated.
  • Striated, since regular arrangement of actin and myosin filaments form cross striation patterns.
  • Interior of muscle is divided into fascicles.
  • Individual muscle fibers are surrounded by connective tissue called endomysium.
  • Fascicles are surrounded by a stronger connective tissue perimysium.
  • A connective tissue covers the entire muscle known as epimysium.
  • For example, biceps brachii.
 
Applied Anatomy
  • Heat rigor occurs above 43oC where the muscle protein gets denatured, as a result muscle remains in a contracted state.
  • Skeletal muscle is capable of limited regeneration. If large regions are damaged, regeneration does not occur and the missing muscle is replaced by connective tissue.
  • Polymyositis is a disease of muscle characterized by inflammation of the muscle fibers.18
 
SMOOTH MUSCLE
  • Involuntary muscle.
  • Present in walls of hollow viscera and blood vessels.
  • Uninucleated, spindle shaped myocytes.
  • Centrally placed single nucleus.
  • Nonstriated, since actin and myosin filaments are arranged randomly and are without cross striation patterns.
  • Present in walls of organs like esophagus, stomach, small intestine, arteries and veins.
 
Applied Anatomy
  • Smooth muscle has got the most good regeneration capacity than any other type of muscle tissue.
  • Leiomyosarcomas are malignant tumors of smooth muscle. The tumor consists of spindle cells with large hyperchromatic nuclei.
  • Hyperplasia means increase in muscle mass. The most common cause is the increase in number of smooth muscle fibers.
  • The contraction of smooth muscle cells is slow, but they can remain contracted for long periods.
  • Smooth muscle cells form the extracellular fibrous tissue components in the tunica media of blood vessels.
  • Smooth muscle cells in the walls of elastic arteries regulate the blood supply to their target tissues.
 
Viva-voce
Q. When the muscle cells are cut in cross section, there are interruptions in the basal laminae. What is responsible for these discontinuities?
Ans. Gap junctions.
Q. Why do smooth muscle fibers in cross section have different diameters and why do some of these fail to show nuclei?
Ans. Smooth muscle cells have tapered ends. Since the cells interdigitate different diameters would be revealed in a particular plane of section and the plane of section does not always go through the nucleus.
Q. Are myofibrils or sarcomeres present in smooth muscle fibers?
Ans. No.19
 
SMOOTH MUSCLE
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  • Presence of single, uninucleated, spindle shaped fibers
  • Presence of centrally placed nucleus.
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CARDIAC MUSCLE
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  • Branching fibers with striations present.
  • Intercalated discs and centrally placed nucleus present.
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CARDIAC MUSCLE
  • Involuntary muscle.
  • It is made up of cylindrical fibers with striations.
  • Cardiac muscle fibers are shorter than skeletal muscle fibers.
  • Contains single central nucleus.
  • Binucleate muscle fibers are occasionally seen.
  • It is present in branching anastomosis.
  • Intercalated discs (gap junction complex) are present at regular intervals.
  • These gap junctions couples all fibers for rhythmic contraction.
  • Cardiac muscle fibers exhibit autorhythmicity.
  • For example, walls of heart, aorta, pulmonary trunk.
 
Applied Anatomy
  • Fibrillation is the abnormal contraction of cardiac muscle.
  • Angina pectoris is episode of chest pain due to temporary ischemia of cardiac muscle.
  • Persistent ischemia due to blockage of coronary arteries results in necrosis (death) of the cardiac muscle.
  • In brown atrophy of heart there will be accumulation of yellowish brown lipid pigment called lipofuscin in the myocardial fibers (Lipofuscin—wear and tear pigment).
 
Viva-voce
Q. What is the position of the nuclei in cardiac muscle cell?
Ans. Central.
Q. Do the myofibrils pass through intercalated discs?
Ans. No.
Q. How can you distinguish cross sections of cardiac muscle fibers from those of skeletal muscle fibers?
Ans. Central nuclei, intercalated discs, branching fibers.22
 
Blood Vessels
 
 
General Aspects
 
Artery Structure
Arterial wall composed of three concentric layers.
  1. Tunica intima
    • Innermost layer.
    • Lined by endothelium with underlying subendothelial connective tissue.
  2. Tunica media
    • Middle layer.
    • Contains smooth muscle, elastic and reticular fibers.
    • Thickest layer of the artery.
  3. Tunica adventitia
    • Outermost layer
    • Contains collagen fibers (type 1) and elastic fibers.
    • Vasovasorum (vessels that supply the vessels) is present which helps in nutrition.
 
Veins Structure
Walls are made up of three layers.
  1. Tunica intima
    • Innermost layer.
    • Lined by endothelium with underlying subendothelial connective tissue.
  2. Tunica media
    • Middle layer
    • Contains smooth muscle, elastic and reticular fibers.
  3. Tunica adventitia
    • Thickest and best developed layer (most contrasting feature of vein with artery).
    • Longitudinal muscle bundles are seen in this layer.
    • Vasovasorum present.
 
LARGE ARTERY OR ELASTIC ARTERY
  • Arterial wall made of three layers, i.e. tunica intima, tunica media and tunica adventitia.
  • Tunica intima consisting of the endothelium and subendothelial connective tissue.
  • Tunica media is the thickest layer.
  • Tunica media made of mainly elastic fibers with few smooth muscle fibers.
  • This feature of elastic artery responsible for Windkessel effect.
  • Vasovasorum present in tunica adventitia.
    “Example: Aorta, common carotid artery, etc.”23
 
LARGE ARTERY
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  • Presence of three layers tunica intima, tunica media and tunica adventitia.
  • Tunica media more prominent with more elastic fiber and few smooth muscle fibers.
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MEDIUM SIZED ARTERY
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  • Thick tunica media with numerous smooth muscle fibers.
  • Presence of internal elastic lamina thrown into folds.
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MEDIUM SIZED ARTERY
  • Also known as muscular artery.
  • Arterial wall made up of three layers.
  • Tunica media thicker than adventitia.
  • Tunica intima consisting of the endothelium and subendothelial connective tissue.
  • Tunica media consists of mainly smooth muscle fibers and few elastic fibers.
  • Internal elastic lamina (elastic fibers) is present between tunica intima and tunica media.
  • External elastic lamina separates tunica media and adventitia.
  • Vasovasorum present in tunica adventitia.
  • For example, radial artery, ulnar artery, brachial artery.
 
Applied Anatomy
  • In old age the arteries become stiff. This phenomenon it called arteriosclerosis.
  • In atherosclerosis usually large and medium sized arteries are affected, where smooth muscles and macrophages within the tunica intima are filled with lipid vacoules with cholesterol esters which crystallise to form needle like structures and produce clefts in intimal tissue.
  • Inflammation of an artery is known as arteritis.
  • Thromboangitis obliterans is inflammation of peripheral arteries of the legs, seen in smokers.
  • The ability of medium sized arteries to decrease their diameter (to vasoconstrict) regulates the flow of blood to different parts of the body as required.
  • The maintenance of blood pressure in the arterial system between contractions of the heart results from the elasticity of large arteries. This quality allows them to expand when the heart contracts and to return to normal between cardiac contractions.
 
Viva-voce
Q. What is pulse?
Ans. Pulse is a pressure wave transmitted along the artery as a result of the ejection of the blood by the ventricles.
Q. What is blood pressure?
Ans. Blood pressure is the measure of the force that the circulating blood exerts against the artery wall.26
 
LARGE VEIN
  • Tubular organ having relatively thin wall and bigger lumen.
  • Thin wall comprises of following: tunica intima, tunica media, tunica adventitia.
  • Tunica intima—consisting of endothelium, small amount of subendothelial connective tissue, and internal elastic lamina.
  • Tunica media—thin circular arrangement of smooth muscle fibers.
  • Tunica adventitia—largely developed, smooth muscles in longitudinal arrangement as bundles, surrounded by connective tissue containing vasovasorum.
  • In large vein tunica media and intima is distinguished by the presence of internal elastic lamina.
  • Longitudinal bundles of smooth muscles are seen as muscular patches in cross section.
  • For example, superior and inferior vena cava.
 
Applied Anatomy
  • Inflammation of an vein is known as phlebitis.
  • Valves are present in veins to prevent the backflow of blood. But in cases of large veins like superior vena cava and inferior vena cava, the valves are absent.
 
Viva-voce
Q. How will you identify longitudinal smooth muscle bundles in a histology slide under microscope?
Ans. The longitudinal smooth muscle fibers bundle are seen as muscular patches on cross section when viewed under microscope.
Q. What is aortocaval compression syndrome?
Ans. Aortocaval compression syndrome, is compression of the abdominal aorta and inferior vena cava by the gravid uterus when a pregnant woman lies on her back, and is a frequent cause of maternal hypotension, which can in result in loss of consciousness.27
 
LARGE VEIN
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  • Presence of 3 layers tunica intima, tunica media and tunica adventitia.
  • Tunica adventitia more prominent with muscular patches seen.
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MEDIUM SIZED VEIN
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  • Presence of three layers tunica intima, tunica media and tunica adventitia.
  • Thin tunica intima with collapsed lumen.
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MEDIUM SIZED VEIN
  • It is made up of 3 layers.
  • Tunica intima, tunica media, tunica adventitia.
  • Internal and external elastic lamina is absent.
  • Tunica media consists of few smooth muscle fibers and elastic fibers, in collagen fibers.
  • Tunica adventitia consists of loose connective tissue.
  • Vasovasorum and nerve fibers are also present in this layer.
  • Lumen is collapsed.
  • For example, saphenous vein, median cubital vein, cephalic vein.
 
Applied Anatomy
  • Endothelial cells and the basal lamina can act as selective filters between the blood and the tissue surrounding the blood vessel.
  • Venous insufficiency is the most common disorder of the venous system, and is usually manifested as spider veins or varicose veins.
  • Deep-vein thrombosis is a condition in which a blood clot forms in a deep vein, which can lead to pulmonary embolism and chronic venous insufficiency.
  • Communicating veins (or perforator veins) are veins that directly connect superficial veins to deep veins which are usually medium sized veins.
  • In neurogenic and hypovolemic shock the smooth muscles surrounding the veins become slack and the veins fill with the majority of the blood in the body, keeping blood away from the brain and cause unconsciousness.
 
Viva-voce
Q. Is there medium sized veins without valves? If so name any one vein.
Ans. Yes, emissary veins present in the head and neck region and the besian veins within the myocardium of heart.
Q. How will you distinguish a medium sized artery and vein of same size lying close to each other?
Ans. The medium sized vein on compression will collapse easily due to less number of smooth muscle fibers, but a medium sized artery due to its thick muscle coat is difficult to compress.30
 
Lymphoreticular System
 
LYMPH NODE
  • It is an oval shaped discrete structure.
  • Consist of capsule, cortex, para cortex and medulla.
  • Capsule: Consisting of connective tissue with arteriole and venule, afferent lymphatic vessel. It sends the trabeculae to interior. It is separated from cortex by subcapsular sinus or marginal sinus to which the afferent lymph vessels empty its contents.
  • Cortex: Consisting of lymphatic nodules with germinal center, are incompletely separated by trabeculae.
  • Lymphatic follicles are made by B lymphocytes.
  • There is a dark zone surrounding the germinal center, which is made up of smaller mature B lymphocytes known as mantle zone.
  • The deeper part of cortex or the para cortex is occupied by T cells.
  • Medulla: Consisting of medullary cords (Anastomosing cords of lymphatic tissues with plasma cells, macrophages and lymphocytes) and medullary sinus (capillary channels that drains lymph through different lymph vessels).
  • Main framework by reticular connective tissues.
 
Applied Anatomy
  • In chronic lymphocytic lymphoma the lymph node architecture is diffusely effaced by tumor cells.
  • Sites of antigenic recognition and antigenic activation.
  • During antigenic activity B cells are converted to centroblasts then into centrocytes.
  • Lymphocytes are relatively small in the medullary sinus than in lymphatic nodules helping to distinguish each other.
  • Lymphadenitis is the inflammation of the lymph nodes and is due to the infection of the body part drained by it.
  • From the primary cancer sites, cancer cells metastases through the lymphatics and get lodged at the lymph nodes draining the corresponding primary site.
 
Viva-voce
Q. What are medullary cords?
Ans. These are anastomosing cords of lymphatic tissues present in the medulla.31
 
LYMPH NODE
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  • Presence of lymphatic nodules in cortex
  • Presence of medullary cords and sinuses in the medulla.
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PALATINE TONSIL
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  • Presence of crypts
  • Presence of subepithelial lymphoid nodule
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PALATINE TONSIL
  • Consists of a protective layer of stratified squamous nonkeratinized epithelium.
  • Invaginated by deep grooves called crypts.
  • A dense connective tissue underlies the tonsil and forms its capsule consisting of some blood vessels.
  • Below the epithelium, numerous lymphatic nodules are distributed and they merge frequently with each other and exhibit lighter staining germinal center.
  • The tonsilar crypts usually contain the dead antigen, broken debris, disarmed bacteria, etc.
 
Applied Anatomy
  • In case of secondary infections, the tonsil is one the lymphoid organ where inflammation is distinctly visible.
  • Mouth of crypts appear as purulent spots in tonsillitis due to infection and pus formation.
 
Viva-voce
Q. What kind of epithelium lines the tonsil?
Ans. Tonsil is lined by stratified squamous nonkeratinized epithelium.
Q. What are crypts?
Ans. The surface of the tonsil is invaginated by deep grooves. These grooves are known as tonsilar crypts.
Q. What does tonsilar crypts contain?
Ans. The tonsilar crypts usually consists of dead antigen, broken debris, disarmed bacteria, etc.
Q. What does germinal center contain?
Ans. Germinal center consist of new and mature lymphocytes. The former is present in the inner aspect and the latter is present in the outer aspect of the germinal center.34
 
SPLEEN
  • Consists of a dense connective tissue capsule from which trabeculae arise and contains trabecular arteries and veins.
  • Does not exhibit cortex and medulla but the capsule divides into compartments called splenic pulps.
  • White pulp is made up of numerous lymphatic follicles which has a germinal center and peripherally located central artery.
  • Red pulp is formed by the diffuse cellular meshwork around the white pulp and act as a single unit. It contains venous sinuses and splenic cords.
  • White pulp is the site of immune response to blood borne antigens, T cells and B cells are present within the nodules.
  • Spleen consists of venous sinuses in contrast to the lymphatic sinuses in lymph nodes.
  • Splenic cords contain macrophages, lymphocytes, plasma cells and different blood cells.
 
Applied Anatomy
  • In spleen lymphatic nodules are found throughout the structure.
  • Spleen does not exhibit subcapsular or subtrabecular sinuses.
  • The capsule and trabeculae in spleen are thicker than those in lymph node.
  • In congestive splenomegaly, there is splenic obstruction due to chronic venous obstruction. Here red pulp is congested early and cirrhosis of the liver is the main cause.
 
Viva-voce
Q. Where do the blood vessels directly open in spleen?
Ans. The blood vessels open into the red pulp giving the characteristic red color.
Q. What are the contents of splenic cords?
Ans. Splenic cords consist of macrophages, lymphocytes, plasma cells and different blood cells.
Q. What are splenic pulps?
Ans. Splenic pulps are the different compartments of the spleen formed by the passage of capsule into the organ.35
 
SPLEEN
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  • Presence of thick capsule and trabeculae.
  • Red pulp containing splenic cords and sinusoids and white pulp present.
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THYMUS
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  • Presence of lobules with lymphoid tissue.
  • Presence of Hassall's corpuscles in the medulla.
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THYMUS
  • Consist of connective tissue capsule from which trabeculae arise and extend into interior dividing the gland into numerous incomplete lobules, blood vessels pass to gland via this.
  • Each lobule consists of dark staining outer cortex and light staining inner medulla.
  • As lobules are incomplete medulla shows continuity between neighboring lobules.
  • Cortex consists of densely packed lymphocytes whereas medulla contains few lymphocytes and more epithelial reticular cells which form Hassall's corpuscle or thymic corpuscle.
  • Hassall's corpuscles are oval structures consisting of aggregations or whorls of flattened epithelial cells and exhibit degeneration.
 
Applied Anatomy
In thymic follicular hyperplasia, there is appearance of numerous B cell germinal centers with in the thymus. Usually this is seen in myasthenia gravis and rheumatoid arthritis.
 
Viva-voce
Q. What are Hassall's corpuscles?
Ans. These are whorls or aggregations of flattened epithelial reticular cells which later undergo degeneration.
Q. Why there is a medullary continuity?
Ans. Since the lobules are incompletely seperated there is medullary continuity between the adjacent lobules.
Q. How do blood vessels and other lymphatic vessels enter the organ?
Ans. The blood vessels and lymphatics enters the capsule and then pass through the trabeculae to enter the thymus.38
 
Nervous Tissue
 
NERVE FIBER
  • Consist of central axon appearing as slender thread which stains lightly.
  • Surrounded by myelin sheath which is not continuous throughout the length of axon, forming interruption called nodes of Ranvier and occurs between adjacent Schwann cells.
  • At the node of Ranvier, the Schwann cell membrane is seen as a thin peripheral boundary that descend towards axon.
  • Around some of the axons a connective tissue layer is also present.
  • A possible Schwann cell nucleus and a fibrocyte is usually associated with it.
  • Outside the axons a capillary with blood cells is also found.
  • Nodes of Ranvier are responsible for saltatory conduction in large myelinated neurons resulting in more efficient and faster conduction.
  • Usually the surrounding myelin sheath will be dissolved by chemicals during preparation and are seen as empty spaces.
 
Applied Anatomy
  • Inflammation of the nerve is known as neuritis.
  • Neuropathy is damage or disease of nerves which may affect sensation, movement, gland or organ function or other health aspects depending on the nerve involved.
  • Neuropraxia is a temporary interruption or physiological block of conduction without loss of axon continuity.
  • Axonotmesis is the loss of relative continuity of the axon and its myelin, but connective tissue framework is preserved.
  • Neurotmesis is the total destruction of the entire nerve fiber.
 
Viva-voce
Q. What are nodes of Ranvier?
Ans. These are interruptions or discontinuities in the myelin sheath surrounding the axon.
Q. Which structure helps to maintain the appropriate microenvironment for peripheral nerve fibers?
Ans. Perineurium.
Q. Which cell type forms the myelin sheath around myelinated axons in the central nervous system?
Ans. Oligodendrocyte.39
 
NERVE FIBER
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  • Axon cylinder seen at the center.
  • Nodes of Ranvier present.
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SPINAL GANGLION
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  • Presence of round pseudounipolar neurons in groups.
  • Presence of nerve fibers in the form of bundles in between ganglion cells.
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SPINAL GANGLION
  • Each ganglion is enclosed by a irregular connective tissue layer that contain adipose cells, nerves and blood vessels.
  • Consists of mainly numerous round pseudounipolar neurons in groups with central nucleus.
  • Numerous fascicles of nerve fibers pass between the neurons. These nerve fibers represent the nerve process formed by bifurcation of a single axon.
  • Regularly arranged nerve fibers enter and leave the ganglion.
  • Contain well-defined satellite cells which are small flat cells that surround the neurons of ganglia of peripheral nervous system and provide structural support for neuronal bodies, insulate them and regulate exchange of different metabolic substances.
  • They are enclosed in a well-defined connective tissue capsule and capsular cells.
 
Applied Anatomy
  • Develops from the neural crest cells and not from the neural tube.
  • The nerve endings of dorsal root ganglion neurons have a variety of sensory receptors that are activated by mechanical, thermal, chemical, and noxious stimuli.
  • Unlike the majority of neurons found in the central nervous system, an action potential in dorsal root ganglion neuron may initiate in the distal process in the periphery, bypass the cell body, and continue to propagate along the proximal process until reaching the synaptic terminal in the dorsal horn of the spinal cord.
 
Viva-voce
Q. What kind of neurons are mainly present in spinal ganglion?
Ans. Pseudounipolar neurons.
Q. What are the suppportive cells present in spinal ganglion?
Ans. Satellite cells which are small flat cells that surround the neurons of ganglia.
Q. Does spinal ganglion have a capsule?
Ans. Yes, spinal ganglion consist of a well-defined connective tissue capsule.42
 
SYMPATHETIC GANGLION
  • Neurons are multipolar and more uniform in size due to which their outlines and their dendritic process appear irregular.
  • Neurons contain eccentric nuclei and may be binucleate and in older individuals a brownish lipofuscin pigment accumulates in cytoplasm.
  • Satellite cells surround multipolar neurons but are less in number compared to spinal ganglion and the connective tissue capsule and cells are not well-defined around the neurons but fibrocytes and venule are usually present.
  • Nerve fibers are not arranged in groups and the nerve fibers are seen irregularly or scattered.
  • The flattened nuclei on the periphery are the Schwann cells.
  • These nerve fibers represent both preganglionic and post-ganglionic axons.
 
Applied Anatomy
  • Responsible for fight or flight response in stress and in impending danger.
  • Neuroblastoma tumor arises from the sympathetic ganglial tissue.
  • If sympathetic nervous system takes control for long durations, it may release the cortisol hormone instead of the adrenaline, which can harm the brain and can cause anxiety, mood swings, hypertension and palpitation of the heart.
 
Viva-voce
Q. What kind of neurons are mainly present in sympathetic ganglion?
Ans. Multipolar neurons.
Q. What are the suppportive cells present in sympathetic ganglion?
Ans. Satellite cells which are small flat cells that surround the neurons of ganglia and fibrocytes.
Q. Does spinal ganglion have a capsule?
Ans. Yes, spinal ganglion consist of a connective tissue capsule which is not so well-defined when compared to that of the spinal ganglion.43
 
SYMPATHETIC GANGLION
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  • Presence of small and scattered multipolar neurons with eccentric nucleus.
  • Presence of satellite cells.
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SEROUS SALIVARY GLAND
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  • Presence of serous acini with round basal nuclei and small lumen.
  • Presence of lobar and interlobular ducts.
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45
 
Oral Cavity and Structures
 
SEROUS SALIVARY GLAND
  • Example: Parotid gland.
  • The gland is surrounded by dense connective tissue capsule from which septa arise and subdivide gland into lobes and lobules.
  • Each lobule consists of pyramidal shaped serous cells (secretory cells) with round basal nuclei that forms the serous acini.
  • Serous acini are surrounded by thin contractile myoepithelial cells.
  • Small secretory granules are visible in the cell apices of serous cells (at high power).
  • In between the lobules, in the connective tissue septa arterioles, venules, and interlobular excretory ducts are located.
  • Some lobules may also contain numerous adipose cells.
  • Secretory acini empty their product into narrow channels, the intercalated ducts the secretory product from intracalated ducts drains into striated ducts and then to intralobular ducts.
 
Applied Anatomy
  • Lymphoid infiltrates of the salivary glands are common to a variety of pathologic conditions including autoimmune disorders, malignant lymphomas, and immunoregulatory responses to parenchymal neoplasms.
  • Mumps affects the parotid gland.
  • Adenoma is one of the benign epithelial tumor that affect the parotid gland.
  • Sialadenitis is the inflammation of the salivary gland.
  • A sialocele is a localized, subcutaneous cavity containing saliva. It is caused by trauma (e.g. surgical trauma) or infection. They are relatively common complication following surgery to the salivary glands, commonly the parotid gland.
 
Viva-voce
Q. What is Frey syndrome?
Ans. After parotidectomy, at times there may be regeneration of secretomotor fibers of auriculotemporal nerve which joins the great auricular nerve. This causes stimulation of sweat glands and hyperaemia in the area of its distribution, thus producing redness and sweating in the area of skin supplied by the nerve.46
 
MUCOUS SALIVARY GLAND
  • Example: Sublingual gland.
  • It contains mucous acini formed by mucous cells with cytoplasm filled with mucous and flat, single, basally located nuclei.
  • Contractile myoepithelial cells are seen around individual mucous acini.
  • Duct system is different, intercalated ducts are short or absent, in contrast, the nonstriated intralobular excretory ducts are more prevalent in the sublingual glands.
  • More abundant interlobular connective tissue septa.
  • Arteriole, venule, nerve fibers and interlobular excretory ducts are seen in the septa.
  • Oval shaped adipose tissues are found scattered in connective tissue of the gland.
  • Saliva is produced after autonomic stimulation.
 
Applied Anatomy
  • Salivary duct calculus may cause blockage of the ducts, causing pain and swelling of the gland because of cysts.
  • Ranula is the name used when a mucocele occurs in the floor of the mouth (underneath the tongue) and may grow to a larger size than mucoceles at other sites, and they are usually associated with the sublingual gland.
  • Sialadenosis (sialosis) is an uncommon, non-inflammatory, non-neoplas tic, recurrent swelling of the salivary glands. The cause is hypothesized to be abnormalities of neurosecretory control and may be associated with alcoholism.
 
Viva-voce
Q. What percentage of the total salivary volime does sublingual gland contribute?
Ans. Only 10% of total salivary volume.
Q. From what structure does sublingual gland develop from?
Ans. They develop from epithelial buds in the sulcus surrounding the sublingual folds on the floor of the mouth, lateral to the developing submandibular gland.47
 
MUCOUS SALIVARY GLAND
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  • Presence of mucous acini with flattened basal nucleus
  • Presence of interlobular and intralobular ducts.
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48
 
MIXED SALIVARY GLAND
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  • Presence of mucous and serous acini with serous demilunes.
  • Presence of lobar and interlobar ducts.
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49
 
MIXED SALIVARY GLAND
  • Example: Submandibular gland.
  • It consist of both serous and mucous acini but mucous acini predominating.
  • Serous cells form cresent shaped cap over the mucous acini and are known as serous demilunes or demilunes of Gianuzzi.
  • Both the serous and mucous acini are covered by the contractile myoepithelial cells along with intercalated ducts.
  • Interlobular connective tissue septa divides the glands into lobules.
  • Located in the connective tissue septa are nerves, arteriole, venule and adipose cells.
  • The duct system of submandibular gland is similar to that of parotid gland.
 
Applied Anatomy
  • Sialolithiasis is a condition where a calcified mass forms within a salivary gland, usually in the duct of the submandibular gland.
  • Sialolithiasis can result in chronic obstructive type of sialadenitis (inflammation).
  • Chronic sclerosing sialadenitis is a chronic (long-lasting) inflammatory condition affecting the salivary gland. It is benign, but presents as hard, indurated and enlarged masses that are clinically indistinguishable from salivary gland neoplasms or tumors.
  • The chorda tympani nerve supplying the secretomotor fibers to subman dibular gland lies medial to spine of sphenoid. Any injury to the spine may involve the nerve and can result in loss of secretion of saliva.
 
Viva-voce
Q. Which muscle divides the submandibular gland?
Ans. Mylohyoid muscle.
Q. Why the submandibular gland have greater chance of getting calculi or small stones?
Ans. Due to the presence of both serous and mucous acini, the secretions from the gland is more viscous as a result there are more chances of getting calculi.50
 
TONGUE
  • Consists of intercalated skeletal muscle fibers.
  • Surface covered by surface elevations called filiform, fungiform and circumvallate papillae.
  • Filiform papillae are the most numerous and smallest that cover tongue, lack tastebuds.
  • Circumvallate papillae are the largest, are in the back of tongue and have furrows, underlying serous glands and tastebuds.
  • Foliate papillae are rudimentary in human.
  • Posterior lingual glands in the connective tissue open onto dorsal surface of tongue.
  • Skeletal muscle fibers are arranged both in longitudinally and transversely.
 
Applied Anatomy
  • The loss of taste sensations in the anterior 2/3rd of the dorsum is mainly due to lesions in facial nerve.
  • The loss of taste from vallate papillae is seen most likely due to lesion of glossopharyngeal nerve or its nucleus.
  • Inspection of tongue helps in diagnosis of various diseases like:
    1. Reddish tongue in glossitis.
    2. Excessive furrowing in prolonged fever.
    3. Black hairy tongue in AIDS.
 
Viva-voce
Q. What are papillae?
Ans. These are surface elevations present on the surface of tongue.
Q. What are the types of papillae present on tongue?
Ans. Filiform, fungiform and circumvallate papillae.
Q. Which papillae contain tastebuds?
Ans. Circumvallate papillae.
Q. Which papillae lack taste buds?
Ans. Filiform papillae.
Q. Where do the posterior lingual glands open into?
Ans. The posterior lingual glands open into the dorsal surface of the tongue.51
 
TONGUE
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  • Presence of different kinds of papillae with skeletal muscle fibers.
  • Presence of glands and stratified nonkeratinized squamous cell lining.
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52
 
ESOPHAGUS
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  • Presence of 4 layers of GIT.
  • Presence of esophageal glands in submucosa.
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Alimentary System
 
 
General Aspects
  • Wall of gastrointestinal tract or the GIT has 4 basic layers:
    1. Mucosa
    2. Submucosa
    3. Muscularis externa
    4. Serosa or adventitia
  • These layers exhibit variations at different sites due to the functional differences of these sites.
    1. Mucosa consists of:
      1. Lining epithelium
      2. Lamina propria
      3. Muscularis mucosa with inner circular and outer longitudinal smooth muscle layers.
    2. Submucosa
      • Located below mucosa
      • Made up of dense irregular connective tissue with numerous blood vessels and lymphatic vessels.
      • Consists of submucosal or Meissner's nerve plexus containing postganglionic parasympathetic neurons controlling the motility of the mucosa as well as secretory activities of associated mucosal glands.
      • In the duodenal region, numerous branched mucous glands are present.
    3. Muscularis externa
      • Thick smooth muscle layer situated inferior to the submucosa.
      • Consists of inner circular and outer longitudinal layers of smooth muscle except at the site of large intestine.
      • Myentric nerve plexus or Auerbach's plexus is located in between these two smooth muscle layers.
      • This plexus contains some postganglionic parasympathetic neurons and controls the motility of intestine.
    4. Serosa and adventitia
      • The visceral organs may or may not be covered by a thin outer layer of squamous epithelium called mesothelium.
      • If the mesothelium covers the visceral organs, the organs will be within the abdominal or pelvic cavity (intraperitonial) and now the outer layer is called serosa.
      • When the visceral organs are not covered by mesothelium, then they will lie outside the visceral cavity (retroperitoneal) and now, outer layer is called adventitia.54
 
ESOPHAGUS
  • Inner lining mucosa made up of stratified nonkeratinized squamous epithelium.
  • Underlying thin layer of connective tissue—lamina propria and layer of longitudinal smooth muscle fiber—muscularis mucosae.
  • Submucosa is wider and consists of adipose tissue, mucous acini of esophageal glands proper and numerous blood vessels such as veins, arteries, etc.
  • The muscularis externa consists of inner circular and outer longitudinal muscle layer separated by thin layer of connective tissue.
  • The adventitia consists of loose connective tissue layer that blends with adventitia of trachea and surrounding structures.
  • Adipose tissue, large blood vessels, artery and vein and nerve fibers are numerous in adventitia.
  • In the upper 1/3, muscularis externa contains skeletal muscle fibers. Middle 1/3 consist of both skeletal and smooth muscle and the lower 1/3 entirely of smooth muscle fibers.
 
STOMACH FUNDUS
  • Posess four layers.
  • Mucosa consists of:
    • Surface epithelium formed by the simple columnar epithelial cells extends into the gastric pits, and lines it.
    • Lamina propria containing gastric glands.
    • Muscularis mucosa extending into lamina propria.
  • Gastric glands consists of five types of cells mainly—parietal (oxyntic) cells producing HCl, chief (zymogenic) cells producing pepsinogen and other digestive enzymes, mucous neck cells producing mucous, endocrine cells—secrete gastrin and serotonin, and undifferentiated (Stem) cells– replace other cells when there is a damage.
  • The subglandular region of lamina propria consists of either lymphatic tissue or small lymphatic nodules.
  • Submucosa forms rugae and consists of capillaries, arterioles, venules and Meissner's nerve plexus.
  • Muscularis externa consists of inner oblique, middle circular and outer longitudinal layers of smoth muscle along with myenteric nerve plexus.
  • Serosa is covered by simple squamous mesothelium of the visceral peritonium and may contain adipose cells.55
 
STOMACH FUNDUS
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  • Presence of 4 layers of GIT
  • Presence of fundic glands, gastric pits and mucosal folds.
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STOMACH PYLORUS
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  • Presence of four layers of GIT
  • Presence of pyloric glands, and abundant mucous neck cells.
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STOMACH PYLORUS
Stomach pylorus consist of four layers.
  1. Mucosa
    • The surface is lined by simple columnar epithelium which extends into and lines all the deeply located gastric pits.
    • Gastric glands are opened into the gastric pits and they produces mucous as well as lysozymes.
    • Lamina propria containing diffuse lymphatic tissue and an occasional lymphatic nodule.
    • Individual smooth muscle fibers from the circular layer of muscularis mucosa pass upwards into lamina propria.
  2. Submucosa contain blood vessels (arteriole and venule) of different size.
  3. Muscularis externa consists of inner oblique, middel circular and outer longitudinal layers of smooth muscles of which the middle layer is more thickened to form the pyloric sphincter.
  4. Serosa is covered by simple squamous mesothelium of the visceral peritoneum and may contain adipose cells.
 
Applied Anatomy
  • In achalasia cardia, the tone of lower esophageal sphincter is increased due to impaired smooth muscle relaxation, causing esophageal obstruction.
  • GERD (gastroesophageal reflux disease) and Barret esophagus:
    • Reflux of gastric contents into the lower part of the esophagus leads to esophagitis.
    • Long standing gastroesophageal reflex may cause replacement of distal squamous mucosa by metaplastic columnar epithelium known as Barret esophagus and esophageal adenocarcinoma.
  • Peptic ulcer: It is chronic, most often solitary lesion that occur in any part of the GI tract exposed to aggressive action of acid/peptic juices.
  • Gastric leiomyosarcoma is rare among gastric malignancies, and only 20% of the cases are located in the gastric cardia or fundus.
  • In pyloric stenosis, there is narrowing of the opening from the stomach to the first part of the small intestine known as the duodenum, due to enlargement (hypertrophy) of the muscle surrounding this opening, which spasms when the stomach empties.58
 
SMALL INTESTINE
 
General Aspects
  • Extends from junction with stomach to join with large intestine or colon.
  • Divided into:
    • Duodenum
    • Jejunum
    • Ileum
  • Mucosa shows plica circularis: The permanent spiral folds, villi—permanent fingerlike projections of lamina propria that extend into intestinal lumen, microvilli—the cytoplasmic extensions that cover the apices of intestinal absorptive cells—all these aids the absorption better.
  • Intestinal glands (crypts of lieberkuhn) are located between the villi at the base throughout the small intestine. Stem cells, absorptive cells, goblet cells, paneth cells and some enteroendocrine cells are also present.
    • Enterocytes (absorptive cells) are involved in the absorption process.
    • Goblet cells are present in between enterocytes and produces mucous secretions.
    • Paneth (zymogen) cells produce lysozymes and other enzymes.
    • Enteroendocrine (enterochromaffin) cells are associated with endocrine function.
  • Besides these, duodenal (Brunner's) glands, Peyer's patches, M-cells, etc. are also seen.
    • Brunner's gland are present in duodenal submucosa.
    • Peyer's patches are present in lamina propria of ileum.
    • M-cells are present along the epithelium above lymphatic follicles.
 
DUODENUM
  • Shortest segment of the small intestine and consist of 4 layers.
  • Mucosa lined by simple columnar epithelium, lamina propria, and muscularis mucosae with connective tissue cells, lymphatic cells, plasma cells, macrophages, smooth muscle cells, etc.
  • Villi in these region are leaf like, tall and numerous with fewer goblet cells in the epithelium.
  • Submucosa consist of mucous duodenal (Brunner's) glands.
  • Muscularis externa consist of two smooth muscle layers, inner circular and outer longitudinal layers.
  • Some parts consist of visceral peritoneum or serosa which is incomplete.59
 
DUODENUM
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  • Presence of 4 layers of GIT
  • Presence of Brunner's glands in submucosa and villi on mucous membrane.
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JEJUNUM
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  • Presence of 4 layers of GIT
  • Presence of intestinal crypts and tongue shaped villi.
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JEJUNUM
  • Consists of four layers.
  • Mucosa is lined by simple columnar epithelium with brush border.
  • The goblet cells lies in between columnar cells and is more in number when compared to duodenum.
  • Shorter, narrower and fewer villi than the duodenum with tongue shape.
  • Lamina propria consists of lymphatic cells, macrophages, smooth muscle cells, blood vessels, etc.
  • Intestinal gland ends at muscularis mucosae.
  • Submucosa lacks Brunner's gland and Peyers patches.
  • Muscularis externa has inner circular and outer longitudinal smooth muscle layers with myenteric plexus present in between them.
  • Visceral peritoneum or serosa surrounds the small intestine.
 
Applied Anatomy (Duodenum and Jejunum)
  • The first part of duodenum is overlapped by liver and gallbladder, either of these structures can adhere to the duodenum, and may be eroded by the duodenal ulcer, if present.
  • It is in the first part of duodenum where majority of ulcers are present.
  • Even gallstones can be extruded from the fundus of a inflammed gallbladder to duodenum and from duodenum to jejunum as well as ileum.
  • In a barium meal procedure, after intake of contrast, the first part of duodenum becomes visible in the radiograph as a triangular shadow called duodenal cap and is emptied to the jejunum every one minute.
  • Intestinal atresia (congenital absence of lumen) and stenosis (narrowing of lumen) is most commonly seen in duodenum and jejunum.
 
Viva-voce
Q. Where are myenteric plexus present?
Ans. Myenteric plexus is present in between the inner circular and outer longitudinal smooth muscle layers.
Q. What kind of epithelium lines the mucosa?
Ans. Simple columnar epithelium with brush border.62
 
ILEUM
  • Consists of four layers.
  • Mucosa is lined by simple columnar epithelium with goblet cells.
  • Villi are thin and slender having lacteals.
  • Lamina propria contains intestinal glands and aggregation of lymphatic nodules called Peyers patches.
  • Usually the lymphatic nodules are seen in close association to each other with indistinct boundaries.
  • Muscularis mucosa is disrupted by Peyer's patches by extending into the submucosa.
  • Muscularis externa having inner circular and outer longitudinal layer of smooth muscle fibers.
  • Serosa having blood vessels and connective tissue.
 
Applied Anatomy
  • Pathogenic microorganisms and other antigens entering the intestinal tract encounter macrophages, dendritic cells, B-lymphocytes and T-lymphocytes found in Peyer's patches and aids immunity.
  • Peyer's patches are present only in ileum throughout the GIT, Brunner's gland is absent in ileum, the villi present are finger shaped.
 
Viva-voce
Q. What are Peyer's patches?
Ans. Lamina propria contains aggregation of lymphatic nodules called Peyers patches.
Q. What type of epithelium lines the ileal mucosa?
Ans. Mucosa is lined by simple columnar epithelium with goblet cells. Specialized epithelilal cells called M-cells are present over Peyer's patches.63
 
ILEUM
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  • Presence of 4 layers of GIT
  • Presence of Peyer's patches and finger shaped villi.
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COLON
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  • Presence of 4 layers of GIT
  • Presence of taenia coli and tubular glands in folds with goblet cells
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COLON
  • Consists of four basic layers.
  • Mucosa is lined by absorptive simple columnar epithelial cells and larger number of mucous filled goblet cells.
  • Lamina propria contains intestinal glands.
  • Muscularis mucosae is well-defined.
  • Submucosa and lamina propria are filled with aggregations of lymphatic cells and lymphatic nodules.
  • Submucosa also contains connective tissue cells and fibers, various blood vessels and nerves.
  • Muscularis externa consists of:
    • Inner circular layer throughout the length of colon.
    • Outer longitudinal layer is condensed into 3 broad longitudinal bands called taeniae coli whose contraction causes sacculations or haustra.
    • Parasympathetic ganglion cells of the myentric nerve plexus are found between the circular and longitudinal muscle layers.
  • Serosa covers transverse colon and sigmoid colon.
  • Serosa shows fat filled peritoneal pockets called appendices epiploicae.
 
Applied Anatomy
Ulcerative colitis is a recurrent ulceroinflammatory lesion of the colon characterized by diffuse inflammation ulcerations, crypt abscess formation, goblet cell depletion and paneth cell metaplasia.
 
Viva-voce
Q. What is taenia coli?
Ans. Outer longitudinal layer of muscularis externa is condensed into 3 broad longitudinal bands called taeniae coli and they extend from base of appendix to caecum.
Q. What are the characteristic features of submucosa of large intestine?
Ans. Submucosa and lamina propria are filled with aggregations of lymphatic cells and lymphatic nodules. It also contains connective tissue cells and fibers, various blood vessels and nerves.66
 
APPENDIX
  • Consist of four basic layers.
  • Mucosa having epithelium containing numerous goblet cells.
  • Lamina propria shows intestinal glands (crypts of Lieberkühn).
  • In appendix villi are absent and it has small angular lumen compared to the thick wall.
  • Lymphatic nodules with germinal center originate in lamina propria and may extend from the surface epithelium to submucosa.
  • Muscularis mucosae is disrupted by lymphatic nodules.
  • Submucosa having numerous blood vessels.
  • Muscularis externa with inner circular and outer longitudinal layer.
  • Para sympathetic ganglia of Myenteric plexus are located in between the smooth muscle layers.
  • Outermost layer is serosa under which adipose cells are seen.
 
Applied Anatomy
  • Appendicitis is the inflammation of the appendix and is a medical emergency.
  • The lymphoid tissue in the mucosa and submucosa is similar to the Peyer's patches in small intestine.
 
Viva-voce
Q. Where are the parasympathetic ganglia of myenteric plexus present?
Ans. Parasympathetic ganglia of myenteric plexus are located in between the smooth muscle layers.
Q. What are the characteristic features of lamina propria of appendix?
Ans. Lamina propria shows intestinal glands (crypts of Lieberkühn) and lymphatic nodules with germinal center originate in lamina propria and may extend from the surface epithelium to submucosa.67
 
APPENDIX
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  • Presence of 4 layers of GIT
  • Lymphatic nodules present in submucosa.
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LIVER
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  • Hexagonally arranged hepatocytes with portal triad.
  • Presence of central vein.
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Liver and Pancreas
 
LIVER
  • Accessory digestive organ.
  • Microscopic structure consists of hexagonal units called hepatic lobules.
  • A central vein is present in the center of each lobule.
  • From central vein radiating plates of hepatocytes and sinusoids are present towards the periphery.
  • Sinusoids are located in between plates of hepatocytes and posses Kupffer cells (macrophagic cells).
  • Hepatic sinusoids are dilated blood channels lined by discontinuous fenestrated endothelial cells.
  • Sinusoids and hepatocytes are separated by a subendothelial peri-sinusoidal space (Space of Disse).
  • At the periphery of each lobule 3-6 portal area/canals are present.
  • Portal canal contains portal triad viz. hepatic artery, portal vein, bile duct and also lymph vessels.
  • Hepatic artery, portal vein and bile duct are covered by fibrocollagenous tissue.
  • Portal area is bounded by a layer of hepatocytes called as the limiting plate.
  • Arterial and venous blood mix at liver sinusoids and open into central vein.
  • Bile canaliculi (tiny channels) are present between hepatocytes which recieve the bile secreted by the liver cells, they converge and open into the bile duct.
 
Applied Anatomy
  • In hepatitis, the limiting plate gets destroyed and is known as Piece meal necrosis.
  • The structural feature of sinusoids help in efficient exchange of substances between hepatocytes and blood.
  • Since bile flow in canaliculi towards bile duct and blood in sinusoids towards central vein, i.e. in opposite direction, the blood and bile does not mix.70
 
GALLBLADDER
  • It is a muscular sac.
  • Its walls consists mucosa, muscularis and serosa.
  • Muscularis mucosa or muscularis interna and submucosa are absent.
  • Mucosa lined by simple columnar epithelium with underlying lamina propria.
  • Lymphatics, blood vessels, loose connective tissue, etc. are present in lamina propria.
  • Mucosal folds are seen in nondistended states.
  • Crypts are seen between mucosal folds and resembles glands.
  • But glands are only present in neck region of the organ.
  • Muscularis layer consists of randomly placed bundles of smooth muscles with interlacing elastic fibers.
  • This layer also contains lymphatics, nerves and blood vessels.
  • Serosa contains connective tissue.
 
Applied Anatomy
  • Usually gallbladder is nonpalpable during clinical examination, but it becomes palpable in cases of jaundice, mucocele and empyema.
  • In cholelithiasis, stones may be present in gallbladder or in biliary passages and can cause obstructive jaundice and obstructive cholecystitis.
  • In cholecystitis the mucosa is ulcerated with areas of necrosis.
 
Viva-voce
Q. What is the distinguishing feature of gallbladder from other part of the gastrointestinal system?
Ans. Submucosa is absent in gallbladder, whereas present in almost all parts of GIT.
Q. What is the characteristic feature of muscularis layer?
Ans. Muscularis layer consists of randomly placed bundles of smooth muscles with interlacing elastic fibers.
Q. What is the characteristic feature of lamina propria of gallbladder?
Ans. Lymphatics, blood vessels, loose connective tissue, etc. are present in lamina propria.71
 
GALLBLADDER
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  • Presence of 3 layers of GIT
  • Absence of submucosa.
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PANCREAS
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  • Presence of pancreatic acini.
  • Presence of islets of Langerhans.
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73
 
PANCREAS
  • Consists of endocrine and exocrine part.
  • Exocrine part forms the major portion and consist of secretory serous acini and zymogenic cells.
  • These are arranged into small lobules bounded by thin intralobular and interlobular connective tissue septa having interlobular ducts and blood vessels.
  • Endocrine part is represented by the isolated pancreatic islets or islets of Langerhans present between serous acini.
  • Each acinus consists of pyramidal shaped protein secreting cells that surround a small lumen. Their ducts are visible as centroacinar cells and the secretions leave via intralobular ducts to interlobular ducts.
  • Islets are separated from acini by a thin layer of reticular fibers and are actually compact clusters of epithelial cells permeated by capillaries and have alpha, beta, delta and F-cells.
 
Applied Anatomy
  • The exocrine part of pancreas is responsible for the production of digestive enzymes like pancreatic amylase, lipase, etc.
  • The pancreas secretes digestive enzymes in the form of inactive precursors called zymogens.
  • Hormones produces by the islets are as follows:
    • Alpha cells: Glucagon
    • Beta cells: Insulin
    • Delta cells: Somatostatin
    • F-cells: Pancreatic polypeptide
 
Viva-voce
Q. What is the characteristic feature of an acini?
Ans. Each acinus consist of pyramidal shaped protein secreting cells that surround a small lumen. Their ducts are visible as centroacinar cells and the secretions leave via intralobular ducts to interlobular ducts.
Q. What is the endocrine part of the pancreas represented by?
Ans. The endocrine part is represented as pancreatic islets or islets of Langerhans.
Q. What is the exocrine part of pancreas formed from?
Ans. Exocrine part consists of secretory serous acini and zymogenic cells.74
 
Respiratory System
 
TRACHEA
  • Tracheal wall consists of mucosa, submucosa, hyaline cartilage and adventitia.
  • Tracheal lumen is lined by pseudostratified ciliated columnar epithelium with goblet cells.
  • The underlying lamina propria contain fine connective tissue fibers and lymphatic tissue.
  • In the deeper part longitudinal elastic membrane is present that divides lamina propria from submucosa.
  • Submucosa consists of connective tissue fibers, tubuloacinar seromucous tracheal gland and ducts opening to tracheal lumen.
  • The ‘C’ shaped hyaline cartilage is present in incomplete ring which form the frame work and is surrounded by connective tissue perichondrium.
  • The chondrocytes in the lacunae are larger and become flatter towards perichondrium.
  • The gap between the posterior ends of cartilage is filled by trachealis muscle.
 
Applied Anatomy
  • Cilia filters out all foreign particles that enter the body during inhalation.
  • Smoking destroys cilia allowing bacteria, viruses, etc. to enter the body and produces diseases like pneumonia.
  • Tracheostomy consists of making an incision on the anterior aspect of neck and opening a direct airway through a direct incision in the trachea.
 
Viva-voce
Q. What is the distinctive structural component wall of the trachea?
Ans. Cartilage rings.
Q. What type of epithelium lines the tracheal lumen?
Ans. Tracheal lumen is lined by pseudostratified ciliated columnar epithelium with goblet cells.
Q. What is the characteristic feature of submucosa layer in trachea?
Ans. Submucosa consists of connective tissue fibers, tubuloacinar seromucous tracheal gland and ducts opening to tracheal lumen.75
 
TRACHEA
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  • Presence of hyaline cartilaginous plates.
  • Presence of mucous and serous glands in lamina propria.
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LUNG
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  • Presence of various bronchioles.
  • Presence of alveoli lined by simple squamous epithelium.
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LUNG
  • Consists of intrapulmonary bronchus (2o or 3o bronchi), bronchiole, terminal bronchiole, respiratory bronchiole and parenchyma.
  • Parenchyma is composed of alveolar duct and alveoli.
  • Intrapulmonary bronchus is identified by surrounding hyaline cartilage plates, lined by pseudostratified ciliated epithelium.
  • Consists of thin lamina propria, small layer of smooth muscle, submucosa with bronchial glands, hyaline cartilage and adventitia.
  • Bronchiole lined by pseudostratified columnar ciliated epithelium, lumen shows mucosal folds, smooth muscle present, adventitia present, glands and cartilage are absent.
  • Terminal bronchiole is lined by ciliated low columnar epithelium, characterized by irregular lumen, smooth muscle layer and adventitia present.
  • Respiratory bronchiole is lined by columnar or cuboidal cells with cilia, thin connective tissue cells with smooth muscle and elastic fibers seen in association with alveoli.
  • Alveolar duct formed from respiratory bronchiole, smooth muscle bundles are present in the rim of the duct.
  • Alveoli lined by thin simple squamous cells, share a common interalveolar septum numerous capillaries are present in these septa, at the free ends of the septa and open end of alveoli narrow band of smooth muscle is present.
 
Applied Anatomy
  • In interstitial lung disease like pulmonary eosinophilia, there will be thickening of alveolar septa with infiltration of eosinophils.
  • In bronchioalveolar carcinoma, the tumor cells lines the alveolar septa and thus giving an alveolar appearance to the tumor.
 
Viva-voce
Q. What is the importance of elastin in the respiratory system?
Ans. Allows for expandability and return to original volume during expiration.
Q. Which cells are responsible from keeping the lungs free from obstructing particulate matter? How do they carry out this function?
Ans. Macrophages (dust cells). By means of phagocytosis.78
 
Renal System
 
KIDNEY
  • Consists of an outermost capsule, i.e. the renal capsule. Beneath it is the outer dark cortex and inner lighter medulla.
  • Cortex consists of both proximal convoluted tubule (PCT) and distal convoluted tubule (DCT), renal corpuscle, interlobular arteries and veins, and medullary rays (formed by straight portions of nephrons blood vessels, and collecting tubules that join in medulla to form collecting ducts) and these do not extend to capsule.
  • Medulla consists of renal pyramids and base of each pyramid is adjacent to cortex and apex forms the renal papilla which projects to minor calyx which is the dilated portion of ureter and they joins to form major calyx which then join to form the renal pelvis.
  • The renal corpuscle consists of Bowman's capsule and glomerulus. Bowman's capsule is made of an outer parietal layer and inner visceral layer. Outer layer is made by simple squamous epithelium and inner layer by specialized cells called podocytes.
  • Glomerulus is made of tuft of anastomosing capillaries lined by fenestrated epithelium.
  • PCT is lined by simple cuboidal epithelium with microvilli giving brush bordered appearance.
  • The thin segment of Loop of Henle is lined by simple squamous epithelium and is permeable to water and sodium whereas thick segment is lined by cuboidal epithelium and is impermeable to water.
  • DCT is lined by simple cuboidal epithelium and is not brush bordered.
  • The collecting tubules are lined by simple cuboidal epithelium whereas collecting ducts are by simple columnar epithelium.
 
Applied Anatomy
In membranous glomerulonephritis there is diffuse thickening of glomerular basement membrane with subepithelial deposit of immunoglobulins.
 
Viva-voce
Q. What is the functional significance of the occurrence of a brush border in the proximal tubule?
Ans. The brush border increases the surface area, facilitating the reabsorption that occurs in the proximal tubule.79
 
KIDNEY
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  • Presence of cortex and medulla with cut sections of PCT, DCT, etc.
  • Presence of medullary rays and renal corpuscles.
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URETER
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  • Presence of star shaped lumen lined by transitional epithelium.
  • Presence of 3 muscle coats.
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URETER
  • Made of three layers:
    1. Mucosa
    2. Muscle coat
    3. Adventitia.
  • Mucosa consisting of transitional epithelium and lamina propria.
  • Lamina propria consists of supporting connective tissue rich in elastic fibers.
  • Mucosa is thrown into folds giving star shaped appearance.
  • Muscle coat—consisting of smooth muscle fibers arranged in 2 layers.
    • Inner longitudinal layer.
    • Outer circular layer.
    • Additional outer longitudinal layer is present in lower 1/3 of ureter located near the bladder.
  • Adventitia is made up of loose connective tissue with blood vessels, lymphatics, nerves and adipose tissue.
 
Applied Anatomy
  • A descending ureteric calculus produces loin to groin pain and is colicky type of pain.
  • A ureteric calculus is often associated with hematuria.
  • When the stone is imapcted, the colic goes off and causes a dull ache.
  • Stone in the ureter is visualized using intravenous pyelography or cystoscopy.
  • Transitional cell carcinoma is a common cause of ureteric cancer and other urinary tract cancers.
 
Viva-voce
Q. What is the functional importance of thick muscular coat?
Ans. Urine is squeezed into the urinary bladder by means of peristalsis.
Q. What is functional importance of folded mucosa?
Ans. The folded mucosa protects against the reflux of urine when the bladder is full.82
 
URINARY BLADDER
  • Consists of three layers:
    1. Mucosal layer
    2. Muscle coat
    3. Adventitia
  • Mucosa—Made of transitional epithelium and lamina propria.
  • Transitional epithelium or urothelium is binucleate and when the bladder is empty it exhibits five to six layers and folds.
  • But when the bladder is distended, the epithelium is thin, consists of 3-4 layers and the superficial cells are flattened.
  • Muscle coat is made up of 3 loosely arranged indistinctive layers of smooth muscle fibers:
    1. Inner longitudinally arranged layer
    2. Middle circularly arranged layer
    3. Outer longitudinally arranged layer
  • Adventitia is made of fibroelastic connective tissue with blood vessels, nerves and lymphatics.
 
Applied Anatomy
  • Transitional epithelium has the following function here:
    • Protects mucosa from being corroded by acidic pH of urine.
    • Acts as an osmotic barrier.
    • They are nonabsorptive in function.
  • Detrusor muscle is layer of urinary bladder wall and problems with this muscle layer can lead to incontinence.
 
Viva-voce
Q. Which part of the urinary bladder can undergo malignant changes?
Ans. Urothelium.
Q. What is the typical feature of transitional epithelium?
Ans. Transitional epithelium is binucleate and when the bladder is empty it exhibits five to six layers and folds and when the bladder is distended, the epithelium is thin, consists of 3-4 layers and the superficial cells are flattened.83
 
URINARY BLADDER
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  • Presence of transitional epithelial lining.
  • Presence of ill-defined muscle coat.
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THICK SKIN
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  • Presence of dermis and thick epidermis.
  • Presence of dermis with sweat glands.
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Skin
 
 
General Aspect
  • Skin, its derivatives and appendages constitute the integument system.
  • Skin consists of two distinct regions viz. epidermis and dermis.
  • These two layers are separated by a basement membrane.
 
Epidermis
  • Superficial region.
  • Lined by keratinized stratified squamous epithelium.
  • Nonvascular.
  • Five layers are seen in this region (from deep to superficial).
    1. Stratum basale
      • Deepest layer of epidermis.
      • Consists of simple columnar cells.
      • Contains specialized sensory cells called as cells of Merkel.
    2. Stratum spinosum
      • Consists of several layers of polyhedral cells.
      • Cells are held together by desmosomes.
    3. Stratum granulosum
      • Made up of 3-5 layers of flattened fusiform shaped cells.
      • Cells contain keratohyaline granules (basophilic) and membrane coating granules.
    4. Stratum lucidum
      • Homogenous glassy layer of flattened dead cells (eosinophillic).
      • Cytoplasm contains keratin.
      • Nuclei and organelles not evident.
    5. Stratum corneum
      • Superficial layer of epidermis.
      • Made up of flattened, nonnucleated, dead, scaly keratinized cells.
      • Cytoplasm filled with keratin.
 
Dermis
  • This region is present inferior to epidermis.
  • It is homologous to lamina propria of mucous membrane.
  • Vascular in nature.
  • Contains dense irregular connective tissue fibers.
  • Dermis can be subdivided into two layers:
    1. Superficial papillary layer
      • Contains sweat glands, loose CT, fibroblasts mast cells, etc.
      • Meissner's corpuscle (sensory receptor) present in this layer.
    2. Deep reticular layer
      • Contains irregular collagenous connective tissue (Type I).
      • Pacinian corpuscle (sensory receptor) present in this layer.86
 
THICK SKIN
  • Epidermis is very thick due to thick stratum corneum layer.
  • Hair follicles and sebaceous glands are absent.
  • Sweat glands are present in dermis.
 
THIN SKIN
  • Epidermis is very thin due to thin stratum corneum.
  • Contains hair follicle and sebaceous glands.
  • Sweat glands present in dermis.
 
Applied Anatomy
  • In squamous cell carcinoma cells of stratum spinosum layer are affected.
  • In psoriasis cells of stratum basale layer proliferate very rapidly and undergo keratinization very early, it leads to increased thickness of skin and raised red patches under white scale.
  • Membrane coating granules present in the cells discharge their contents into granular layer providing the epidermis a sealing effect against foreign materials.
 
Viva-voce
Q. What are the cell junctions in the stratum spinosum?
Ans. Desmosomes
Q. Where are the melanocytes located?
Ans. Stratum basale
Q. Where are cells of Merkel present?
Ans. Stratum basale
Q. Where are Meissner's corpuscles present?
Ans. Superficial papillary layer of dermis
Q. Where are Pacinian corpuscles present?
Ans. Deep reticular layer of dermis.
Q. What are the characteristic features of stratum lucidum layer?
Ans. Homogenous glassy layer of flattened dead cells, cytoplasm contains keratin, and nucleus and organelles are not evident.87
 
THIN SKIN
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  • Presence of dermis and epidermis
  • Presence of dermis with hair follicles and sebaceous glands.
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CORNEA
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  • Presence of anterior limiting lamina.
  • Presence of thick substantia propria with keratocytes.
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Special Senses
 
CORNEA
  • It is a thick, transparent, and a nonvascular structure.
  • It is composed of 5 layers.
  • Anterior (corneal) epithelium made up of nonkeratinized stratified squamous epithelium.
  • Bowman's membrane (anterior limiting membrane): Acellular layer made up of compactly packed collagen fibers.
  • Corneal stroma (Substantia propria) consists of bundles of collagen fibers arranged in layers, parallel to surface of cornea.
  • Descemet's membrane (posterior limiting membrane): Made up of collagen fibers, seperates substantia propria from endothelium.
  • Corneal endothelium is lined by a single layer of squamous epithelium, it forms the posterior surface of cornea.
 
Applied Anatomy
  • Due to its avascular nature:
    1. Transparency of cornea is maintained.
    2. Chances of endogenous infections are rare.
    3. Corneal transplants are not immunologically rejected.
  • Corneal abrasion involves loss of surface epithelial layer due to trauma.
  • In corneal dystrophy one or more parts loses its normal clarity.
  • Corneal neovascularization is due to excessive ingrowth of blood vessels from limbal vascular plexus into the cornea caused by lack of oxygen from air.
 
Viva-voce
Q. What is Descemet's membrane made up of?
Ans. It is made up of collagen fibers, seperates substantia propria from endothelium.
Q. What is the other name of anterior limiting membrane?
Ans. Bowman's membrane.
Q. What kind of epithelium line the corneal endothelium?
Ans. Corneal endothelium is lined by a single layer of squamous epithelium.90
 
RETINA
  • Innermost coat of the eyeball.
  • In total, retina is made up of 10 layers.
  • Pigment layer made of pigmented cuboidal cells.
  • Nervous layer is a layer made by outer and inner segments of rods and cones whose tips are surrounded by processes of pigment cells.
  • External limiting membrane separates rods and cones from the dense outer nuclear layer.
  • Outer nuclear layer contains the nuclei of rods and cones and outer processes of Müller's cells.
  • Outer plexiform layer, where the axons of rods and cones synapses with dendrites of horizontal cells.
  • Inner nuclear layer is a dense layer of cell bodies of bipolar neurons.
  • Inner plexiform layer where the axons of bipolar cells synapses with dendrites of ganglion and amacrine cells.
  • Ganglion cell layer contains cell bodies of ganglion cells and neuroglial cells.
  • Optic nerve fiber layer is made up of bundles of unmyelinated axons of ganglion cells and inner fibers of Müller's cells.
  • Internal limiting membrane—formed by expanded basal ends of Müller's cells with there basement membrane.
 
Applied Anatomy
  • In nonproliferative type of diabetic retinopathy, there will be thickening of capillary basement membrane. Whereas in case of proliferative type of diabetic retinopathy there will be neovascularization of retina.
  • Retinoblastoma: Most common tumor of childhood. It arises from retinal neurons.
  • Since pigment cell layer more firmly attached to choroid than to nervous layer, in myopies retinal detachment usually occurs, leading to blindness.
  • Posterior (¾) part of retina is called as optic part since photosensitive and derived from the walls of optic cup.
 
Viva-voce
Q. What are Müller's cells?
Ans. These are supportive cells for the neurons of retina and have the ability of dedifferentiation to form particular cells when there is injury.91
 
RETINA
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  • Presence of 10 layers.
  • Presence of external and internal limiting lamina.
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OPTIC NERVE
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  • Presence of 3 layers of meninges.
  • Presence of central artery and vein along with nerve fiber bundles.
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OPTIC NERVE
  • It is covered by dura mater, arachnoid mater and pia mater.
  • Within the covering bundles of nerve fibers surrounded by astrocytes are seen.
  • Each bundle contains many myelinated nerve fiber axons of varying caliber.
  • Nerve fibers are derived from the ganglion cells of retina.
  • These bundles also contains small number of pupilomotor fibers and some centrifugal fibers.
  • A central artery and vein are present at the center.
 
Applied Anatomy
  • Optic nerve is not covered by neurilemma, which is present in other peripheral nerves, as a result optic nerve can not regenerate when it is cut.
  • The optic nerve fibers develops from the nerve fiber layer of retina which grow into optic stalk by passing through choroidal fissure and pass posteriorly into brain.
  • Lesions of the optic nerve is characterized by marked loss of vision or complete blindness on the affected side and associated with loss of direct light reflex in the ipsilateral side.
  • Common lesions of optic nerve include optic atrophy, trauma, avulsion, indirect optic neuropathy, acute optic neuritis, etc.
  • Congenital anomalies of optic nerve include medullated or opaque nerve fibers and result in enlargement of blind spot.
 
Viva-voce
Q. What are the supportive cells present in optic nerve?
Ans. Astrocytes
Q. From which structure does nerve fibers of optic nerve develop from?
Ans. Nerve fibers are derived from the ganglion cells of retina.94
 
Female Reproductive System
 
MAMMARY GLAND
  • Consists of mainly parenchyma and stroma.
  • Both of these components differ in case of lactating gland as well as a nonlactating one.
In nonlactating gland:
  • Parenchyma consists of less glandular tissue, poorly developed alveoli having solid cord of cells, extensive branching of duct system, duct lumen poorly visible, tubules and ducts are lined by cuboidal epithelium.
  • Stroma contains more connective tissue and adipose tissue, interlobular connective tissue septum is thick, abundant intralobular loose connective tissue with numerous fibroblasts.
In lactating gland:
  • Parenchyma having more glandular tissue with proliferated tubules enlarged to alveoli which is highly developed, external branching of alveolar ducts and large ducts being lined by stratified epithelium.
  • Lumen filled with milk and contain fat droplets.
  • Stroma: Less connective tissue and adipose tissue, interlobular connective tissue septum is thin, intralobular connective tissue is less and contain lymphocytes and plasma cells.
 
Applied Anatomy
  • In normal mammary gland alveoli are small and few in number whereas in lactating one alveoli are enlarged and distended and number of ducts also increase.
  • The cancers arising from the ductal portion of breast is called ductal carcinomas and cancers arising from the lobules is called lobular carcinoma.
  • Metastasis from one breast to another or to other sites can occur.
 
Viva-voce
Q. What are the major hormones responsible for the cyclic changes in the mammary gland?
Ans. Estrogen and progesterone.95
 
MAMMARY GLAND
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  • Presence of secretory acinar tissue.
  • Presence of intralobular CT, interlobular CT and their ducts.
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OVARY
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  • Presence of follicles with oocytes in different stages of maturity.
  • Presence of germinal epithelium.
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OVARY
  • Lined by simple cuboidal epithelium called as germinal epithelium which is continuous with mesothelium of peritoneum.
  • Beneath the epithelium a layer of dense connective tissue is present called tunica albuginea.
  • Exhibits cortex and medulla arrangement.
  • Cortex occupies the most part and contains stroma (dense reticular fibers and spindle shaped cells with no fibrils) and ovarian follicles of different stages (also atretic follicles, corpus luteum, corpus albicans).
  • Medulla is made of loose fibroelastic connective tissue and contains blood vessels, lymphatics and nerves and is continuous with the mesovarium of peritoneum.
  • The primary ovarian follicles and corpus luteum follicles posses a large central cell and a surrounding flattened cell layer whereas secondary follicle is multilayered.
  • And the largest of all the graafian follicle is seen with varying sizes and lines near surface and consists of:
    1. Oocyte surrounded by ooplasm or yolk.
    2. Ovum covered by zona pellucida.
    3. Surrounded by membrana granulosa having cumulus oophorus and discus proligerus and a follicular cavity embedded in it called antrum folliculi.
    4. Theca folliculi comprising of theca externa and theca interna.
 
Applied Anatomy
  • Polycystic ovary: It is a condition characterized by presence of numerous cysts in the ovary. The cysts are lined by granulosa cells.
  • Mucinous tumor of ovary: Also cystic tumors, it composes of hundreds of cysts which are filled with mucin.
 
Viva-voce
Q. What is the lining epithelium of ovary?
Ans. Lined by simple cuboidal epithelium called as germinal epithelium.
Q. What is the primary ovarian source of estrogenic hormones?
Ans. Granulosa cells.98
 
FALLOPIAN TUBE
  • Also known as uterine tubes.
  • Made up of three layers:
    1. Mucosa
    2. Muscle coat
    3. Serosa
  • Mucosa includes lining epithelium and lamina propria.
  • Lined by simple ciliated columnar epithelium.
  • Apart from ciliated columnar cells, it also contains some nonciliated secretory peg cells.
  • Ciliated columnar cells are short and is more prominent in the proliferative phase.
  • Nonciliated peg cells are longer than ciliated columnar cells.
  • Mucosa consists of extensive folds, as a result the lumen becomes highly irregular which help in providing nutrition to fertilized ovum from all sides.
  • Muscle coat is made of two layers smooth muscles:
    1. Inner circularly arranged layer.
    2. Outer longitudinally arranged layer.
  • Serosa consisting of mesothelium (peritoneum of broad ligament) and supported by connective tissue.
 
Applied Anatomy
  • Tubal obstruction forms one of the major causes of infertility in females.
  • Tubal patency is assesed by using procedures like hysterosalpingography, laproscopy.
  • Surgical removal of fallopian tubes is called as salpingectomy.
  • Propulsion of gametes and embryos is achieved by complex interaction between muscle contractions, ciliary activity and the flow of tubal secretions.
 
Viva-voce
Q. What is the lining epithelium of mucosa of fallopian tube?
Ans. Lined by simple ciliated columnar epithelium and nonciliated secretory peg cells.
Q. What are the characteristics of columnar cells in proliferative phase?
Ans. The columnar cells are prominent and short in the proliferative phase.99
 
FALLOPIAN TUBE
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  • Presence of 1°, 2°, 3° mucosal folds and its lumen.
  • Presence of circular muscle coat.
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UTERUS
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  • Presence of thick myometrium with smooth muscle.
  • Presence of uterine glands in endometrium.
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UTERUS
 
Proliferative Phase
  • Made up of three layers (outer to inner):
    1. Perimetrium (serosa)
    2. Myometrium (Muscle coat)
    3. Endometrium (mucosa)
  • Perimetrium is lined by simple squamous epithelium, supported by connective tissue and contains numerous blood vessels and elastic fibers.
  • Myometrium is a thick muscular layer, composed of smooth muscle fibers arranged in three indistinctive layers:
    1. Outer longitudinal layer.
    2. Middle circular layer (Thickest of the three).
    3. Inner longitudinal layer.
  • Myometrium is highly vascular having areolar tissue, blood vessels and lymphatics.
  • Endometrium lined by simple columnar epithelium. Beneath it, a layer called lamina propria is present which is highly cellular.
  • Lining epithelium extends down into the lamina propria and forms long tubular uterine glands.
  • Uterine endometrium is divided into superficial stratum functionalis and deep stratum basalis.
 
Applied Anatomy
  • Leiomyoma: Benign tumor of smooth muscle affecting the uterus.
  • It is seen in uterus mainly at 3 sites: Submucosa, intramural and subserosa.
  • Adenomyosis: Islands of endometrial tissue found deep in the myometrium.
  • It is mainly the stratum functionalis where the changes occur in response to hormones and is usually shed when fertilization do not occur.
 
Viva-voce
Q. What are the layers of uterine endometrium?
Ans. Uterine endometrium is divided into superficial stratum functionalis and deep stratum basalis.102
 
PLACENTA
  • Consists of fetal portion and as well as maternal portion.
  • Fetal portion is formed by chorionic plate and its villi.
  • Maternal portion is formed by the decidua basalis of endometrium.
  • The chorionic plate is formed by:
    • Trophoblast cells are present just below the connective tissue layer, which is located below the lining of amniotic surface.
    • Section shows cross sections of chorionic villi of different sizes and shapes scattered in intervillous spaces filled with maternal blood.
  • In early stages of pregnancy
    • The chorionic villi form chorionic plate which contain
      1. Connective tissue core.
      2. Fetal blood vessels (including branches of umbilical arteries and vein).
      3. Mesenchyme cells.
      4. Macrophages.
    • The villi are separated by intervillous space.
    • Maternal blood reaches the intervillous space through spiral arteries of decidua and baths the villi containing fetal blood cells.
  • In full term of pregnancy
    • The chorionic villi shows:
      • Chorionic epithelium reduced to syncytiotrophoblast.
      • Connective tissue having more fibers and fibroblasts.
      • Fetal blood vessels of increased complexity.
      • The intervillous space surrounded by maternal blood cells.
 
Applied Anatomy
  • Placental site trophoblastic tumor: It is a trophoblastic tumor mainly composed of monomorphic population of intermediate trophoblasts. The tumor cells are irregular, large polyhedral cells with hyperchromatic nuclei.
  • Choriocarcinoma: This is also a carcinoma affecting placenta arising from the trophoblast.
 
Viva-voce
Q. What are the parts of placenta?
Ans. Fetal part formed by chorionic plate and villi and maternal portion by decidua basalis.103
 
PLACENTA
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  • Chorionic villi of different stages seen.
  • Intervillous space filled with maternal blood and RBCs.
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UMBILICAL CORD
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  • Presence of 2 umbilical arteries and 1 umbilical vein.
  • Presence of Wharton's jelly.
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UMBILICAL CORD
  • Consists of single umbilical vein, 2 umbilical arteries, Wharton's jelly, and a layer of amnion.
  • Umbilical vein is a thin walled structure with wider lumen and bring oxygenated blood from placenta to fetus.
  • Umbilical artery is thick walled in nature and has a narrow lumen and takes deoxygenated blood from fetus to placenta.
  • Wharton's jelly is a mass of gelatinous mucoid connective tissue which hold together the umbilical vessels.
  • A thin single layered amnion covers all the above structures.
  • Amnion is made up of single layer of cuboidal epithelium.
 
Applied Anatomy
  • The nonpatent obliterated part of umbilical artery is the medial umbilical ligament.
  • The umbilical vein of the newborn baby is used as a site for regular transfusion in case of hemolytic disease of newborn since umbilical vein remains patent for atleast a week after birth.
  • After a week since birth the umbilical vein is completely obliterated and is replaced by a fibrous cord called ligamentum teres of liver.
 
Viva-voce
Q. What is Wharton's jelly?
Ans. Wharton's jelly is a mass of gelatinous mucoid connective tissue which hold together the umbilical vessels.
Q. What is the function of umbilical artery?
Ans. Umbilical artery is thick walled in nature and has a narrow lumen and takes deoxygenated blood from fetus to placenta.
Q. What is the function of umbilical vein?
Ans. Umbilical vein is a thin walled structure with wider lumen and bring oxygenated blood from placenta to fetus.
Q. What is the lining epithelium of amnion?
Ans. Single layer of cuboidal epithelium.106
 
Male Reproductive System
 
TESTIS
  • Each testis is enclosed within an outer thick connective tissue capsule called tunica albuginea and inner vascular layer of loose connective tissue called the tunica vasculosa.
  • Connective tissue that extend inward into the testes and surrounds, binds, supports the seminiferous tubules is called interstitial connective tissue.
  • Thin fibrous septa divides the testes into compartments called lobules.
  • Within each lobule one to four seminiferous tubules are present.
  • Seminiferous tubules are lined with stratified epithelium called germinal epithelium containing spermatogenic cells producing sperms.
  • Germinal epithelium roots on basement membrane.
  • Supportive Sertoli cells in the seminiferous tubules nourishes the developing sperm and produces hormones like inhibin, anti-Müllarian hormone, etc.
  • Leydig cells (interstitial cells) situated in the interstitial connective tissue produces testosterone.
  • Alongwith the Leydig cells, clusters of epithelial cells, blood vessels, loose connective tissue cells are also present in the interstitial connective tissue.
 
Applied Anatomy
  • Seminoma is the most common testicular tumor arising from germ cells.
  • Cryptorchidism is undescent of testis which can predispose to testicular tumors.
  • Leydig cell tumors are functional tumors (hormone producing) arising from the interstitial cells of Leydig.
 
Viva-voce
Q. What is the difference between spermatogenesis and spermiogenesis?
Ans. Spermatogenesis is entire the process of formation of sperm from stem cell to spermatozoon. Spermiogenesis is the maturation process from spermatid to spermatozoon.
Q. What are the components of the blood-testis barrier and what is its significance?
Ans. Tight junctions between Sertoli cells isolate developing sperm from the vasculature (prevent their immunological rejection).
Q. What is the primary source of testosterone?
Ans. The Leydig cells.107
 
TESTIS
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  • Presence of seminiferous tubules with spermatozoa.
  • Presence of interstitial cells between the tubules.
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108
 
EPIDIDYMIS
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  • Presence of highly convoluted efferent ductules with stereocilia.
  • Presence of smooth muscle around the ductules.
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EPIDIDYMIS
  • Contains highly convoluted efferent ductules called ductus epididymis
  • These are surrounded by connective tissue and thin smooth muscle layer.
  • Lumen of ductus epididymis is lined by pseudostratified columnar epithelium with 2 types of cells:
    1. Tall columnar principal cells.
    2. Small basal cells.
  • The tall columnar cells bear microvilli called stereocilia.
  • Some parts of the ductus contain mature sperm.
 
Applied Anatomy
  • The stereocilia present in the epididymis are responsible for the absorption and removal of the sperm which fails to leave the epididymis.
  • The name stereocilia is a misonomer as it does not move like the other cilia, and it is moreover like the villi of gut.
 
Viva-voce
Q. Where is the principal site of storage and mobility acquisition of spermatozoa in the male reproductive system?
Ans. Epididymis.
Q. What are the two types of cells present in the lining of lumen of epididymis?
Ans. Tall columnar cells and small basal cells.110
 
VAS DEFERENS
  • Consists of mainly three layers.
  • Mucosa is lined by pseudostratified columnar epithelium and provided with stereocilia in extra-abdominal part of the duct.
  • The mucosa is thrown into longitudinal folds which permit expansion of the duct during ejaculation.
  • Underlying lamina propria consists of compact collagen fibers and a fine network of elastic fibers.
  • Muscular layer consists of three smooth muscle layers an layer:
    • Thin inner longitudinal layer
    • Thick middle circular layer, and
    • Thinner outer longitudinal layer.
  • Adventitia is made up of fibroelastic connective tissue having abundant blood vessels, venules, arterioles and nerves.
  • The lumen may carry sperms.
 
Applied Anatomy
  • The unexpelled sperms produced daily are mainly absorbed by the pseudostratified columnar epithelium of vas deferens. And the absorbed sperms are engulfed and lysed by the macrophages.
  • The same thing happens in men who has undergone vasectomy procedure.
 
Viva-voce
Q. What type of epithelium lines the mucosa of vas deferens?
Ans. Mucosa is lined by pseudostratified columnar epithelium and has stereocilia in extra-abdominal part of the duct.
Q. What does lamina propria of vas deferens contain?
Ans. Lamina propria consists of compact collagen fibers and a fine network of elastic fibers.111
 
VAS DEFERENS
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  • Presence of narrow irregular lumen with mucosal folds.
  • Presence of thick circularly arranged muscle coat.
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PROSTATE GLAND
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  • Presence of prostatic acini separated by fibromuscular tissue.
  • Presence of amyloid body.
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PROSTATE GLAND
  • Prostate is covered by
    • Inner capsule—formed by condensation of fibromuscular stroma.
    • False capsule—formed by pelvic fascia.
  • It is composed of 30-50 branched tubuloalveolar glands embedded in fibromuscular stroma.
  • The ducts of the gland opens into prostatic urethra which is lined by transitional epithelium.
  • The parenchyma is made up of large irregular prostatic alveoli with wide lumen which is lined by epithelium varying from cuboidal to columnar depending on its activity.
  • The lumen of prostatic alveoli contain condensed prostatic secretions called prostatic concretion or amyloid bodies.
  • The fibromuscular stroma supports the parenchyma and is made of smooth muscle fibers with connective tissue fibers.
  • Stroma also contain blood vessels, lymphatics and nerves.
 
Applied Anatomy
  • In nodular hyperplasia of prostate, there will be hyperplasia of all 3 tissue elements—glandular, fibrous and muscular, in which glandular hyperplasia predominates.
  • In adenocarcinoma of prostate, malignant acini have little or no stroma between them.
  • Prostatic secretions along with the secretions from seminal vesicles from major part of semen.
 
Viva-voce
Q. What are prostatic concretions?
Ans. The lumen of prostatic alveoli contain condensed prostatic secretions called prostatic concretion or amyloid bodies.
Q. What is the type of epithelium lining the prostatic alveoli?
Ans. The prostatic alveoli is lined by cuboidal to columnar type of epithelium depending on its activity.
Q. What is fibromuscular stroma of prostate made of?
Ans. The fibromuscular stroma is made of smooth muscle fibers and connective tissue fibers.114
 
Endocrine System
 
ADRENAL GLAND
  • Consist of capsule, cortex, medulla.
  • Cortex—Consists of the following layers from outer to inner.
    • Zona glomerulosa—Cells arranged in clumps (inverted ‘U’ shape), cytoplasm stains pink.
    • This layer produces mineralocorticoids.
    • Zona fasciculata—Widest layer, cells arranged in vertical columns or radial plates, lightly stained due to the presence of numerous lipid droplets.
    • This layer produces glucocorticoids.
    • Zona reticularis—Close to medulla, cells form anastomosing cords.
    • This layer produces sexcorticoids.
  • Medulla—Not sharply demarcated from cortex.
    • Consists of polyhedral cells which modified sympathetic neurons and are seen singly or in groups.
    • The cell groups are separated by wide sinusoidal capillaries.
    • Adrenal medullary cells produces adrenaline and noradrenaline.
    • After tissue fixation fine brown granules become visible in cells called chromaffin cells indicating presence of medullary hormones.
    • The hormones produced by cortex are:
      1. Zona glomerulosa—Mineralocorticoid.
      2. Zona fasciculata—Glucocorticoid.
      3. Zona reticularis—Sex corticoids.
    • The hormones synthesized by medulla include:
      1. Epinephrine.
      2. Norepinephrine.
 
Applied Anatomy
Pheochromocytoma: They are tumors arising from chromaffin cells of the adrenal medulla. The tumor cells are polygonal in shape and are arranged in groups surrounded by a fibrovascular septa.
 
Viva-voce
Q. How is medullary function regulated?
Ans. Through presynaptic nerves and glucocorticoids.115
 
ADRENAL GLAND
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  • Presence of cortex and medulla.
  • Presence of secretory cells and sympathetic neurons.
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THYROID GLAND
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  • Presence of thyroid follicles filled with colloid.
  • Presence of parafollicular cells.
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THYROID GLAND
  • Consists of mainly follicular cells.
  • Follicular cells are arranged spherically into follicles.
  • These follicles are the structural and functional units of thryoid gland.
  • In highly active follicles, epithelium is cuboidal whereas in less active ones the epithelium is flat.
  • All follicles are filled with colloid but some of them may show retraction due to preparation.
  • Parafollicular cells are seen within follicular epithelium or in between follicles.
  • Surrounding the thyroid follicles and follicular cells, thin interfollicular connective tissue is present containing blood vessels and capillaries.
  • The follicular cells are responsible for the production of thyroid hormones.
  • Parafollicular cells secrete calcitonin.
 
PARATHYROID GLAND
  • They lie in close relation to thyroid gland.
  • Glands are covered by a connective tissue capsule from which septa extend into the substance of the gland.
  • The stroma is formed by a network of reticular fibers and adipocytes.
  • The parenchyma consist of mainly two types of cells viz. chief cells and oxyphil cells which are arranged in a cord like manner.
  • The chief cells are small round cells with vesicular nuclei.
  • The oxyphil cells are larger cells with granules.
  • The chief cells produce parathormone.
  • The oxyphil cells have the ability to produce autocrine/paracrine factors (Parathyroid hormone-related protein and calcitriol).
 
Applied Anatomy
  • In Graves disease, the follicular epithelial cells are tall and thrown into as small papillae. The papillae project into lumen of the follicle.
  • In Hashimoto thyroiditis, the thyroid tissue shows dense infiltration lymphocytes and plasma cells. The lymphocytes form lymphoid follicles with germinal centers.118
 
PITUITARY GLAND
  • Mainly divided into adenohypophysis and neurohypophysis.
  • Adenohypophysis consisting of pars distalis (anterior lobe), pars tuberalis, pars intermedia.
  • Neurohypophysis consisting of pars nervosa, infundibulum, and median eminence.
  • Pars nervosa forms the largest portion of neurohypophysis.
  • Pars distalis consists of chromophobe cells (cells that do not take stain), and chromophil cells (cells that take stain—acidophils, basophils).
  • Pars intermedia contains colloid filled cystic follicles.
  • Pars nervosa consists of axons and supporting pituicytes with oval nuclei. It also contain accumulation of neurosecretory material called herring bodies.
 
Applied Anatomy
  • Pituitary adenomas: In this condition there will be presence of tumor cells arranged in nests surrounded by thin connective tissue. Cells can also be arranged in cord like manner.
  • Damage to hypothalamus which stores antidiuretic hormone produced by neurohypophysis, causes deficiency of ADH and leads to diabetes insipidus.
 
Viva-voce
Q. What kinds of cells are in the neurohypophysis?
Ans. Pituicytes (glia), endothelial cells.
Q. What do Herring bodies represent?
Ans. Sites for storage or degradation of neurotransmitters.
Q. What hormones might you expect to find in Herring bodies?
Ans. Vasopressin (antidiuretic hormone) and oxytocin.
Q. Where are the hormones of the neurohypophysis synthesized?
Ans. Hypothalamus.
Q. What are chromophil and chromophobe cells?
Ans. Chromaphobe cells are cells that do not take stain, and chromophil cells are cells that take stain and includes acidophils, basophils.
Q. What is the functional significance of the hypothalamohypophyseal system?
Ans. It allows for rapid and direct delivery of hypothalamic products with releasing and inhibiting effects on anterior pituitary cells.119
 
PITUITARY GLAND
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  • Presence of pars anterior with acidophils and basophils
  • Presence of pars nervosa with pituicytes and pars intermedius with colloid.
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SPINAL CORD
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  • Presence of H shaped gray mater.
  • Presence of central canal.
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Central Nervous System
 
SPINAL CORD
  • In the TS of thoracic segment of spinal cord, we can see gray matter inside and white matter on the periphery.
  • Gray matter is almost an H shaped or butterfly shaped structure.
  • Each half of the gray matter can be divided into three portions namely:
    1. Anterior gray horn: Large anterior mass, this region consists of multipolar motor neurons.
    2. Posterior gray horn: Narrow and elongated part, which is located posteriorly, Clark's column or dorsal nucleus is present in the medial part of the base of the posterior horn.
    3. Lateral gray horn: It is a wedge shaped lateral projection of gray matter between anterior and posterior gray horns. This region consists of sympathetic preganglionic visceral motor neurons.
  • Lateral gray horn is limited to the thoracic and upper two lumbar segments of spinal cord.
  • Two half's of gray matter is connected by the gray commissure at the midline.
  • A central canal is present at the midpoint of horizontal limb of H.
  • Central canal is lined by ependymal cells and it represents the lumen of neural tube.
  • White matter which lies in the periphery is divided into two half's: Right and left
    1. Anteriorly by anterior median fissure.
    2. Posteriorly by posterior median septum.
  • Anterior spinal artery is present in the anterior median fissure.
  • Similar to gray matter, the white matter of each half can be divided into three portions:
    1. Anterior white column: White matter anterior and medial to anterior gray horn.
    2. Posterior white column: White matter medial to posterior gray horn.
    3. Lateral white column: White matter lateral to anterior and posterior gray horns.
  • White matter of each half is connected to each other anteriorly by the anterior white commissure.
  • A sulcus is present just behind the posterior most end of posterior median septum called as posterior median sulcus.
 
Applied Anatomy
  • Damage to lateral horn can lead to Horner's syndrome.
  • Poliomyelitis: Inflammation of gray matter of spinal cord.122
 
CEREBELLUM
  • Cortex is highly folded.
  • These folds are called cerebellar folia.
  • Folds are separated by transverse fissures called sulci.
  • Folium contains an inner core of white matter and an outer cortex of gray matter covered by the thin connective tissue called pia mater.
  • Cortex consists of 3 layers:
    • External molecular layer: Superficial layer, thick, and made of nerve fibers and cells: stellate cells above and basket cells below.
    • Purkinje cell layer: Made up of Purkinje cells (Large sized, flask shaped neurons arranged between molecular and granular layer in single row).
    • Dendrite of Purkinje cells synapses with axons of granular cells.
    • Granular layer: Densely packed with very small granule neurons (smallest cells in the body), they exhibit intensly stained nuclei, few Golgi cells are also present.
    • Dendrite of granule cells and axons of Golgi cells synapses with mossy fibers to form glomeruli (lightly stained).
    • Mossy fibers are afferent fibers ending in granular layer.
    • White matter consists of myelinated nerve fibers.
 
Applied Anatomy
  • Rett syndrome is a cerebellar pathology characterized by loss of Purkinje cells, atrophy, astrocytic gliosis of the molecular and granular layers.
  • Cerebellar diseases result in lack of coordination and disturbances of accuracy movements causing a constellation of symptoms and motor signs.
 
Viva-voce
Q. What are Purkinje cells?
Ans. These are large sized, flask shaped neurons arranged between molecular and granular layer in single row.
Q. What are the characteristics of granular layer?
Ans. The layer is densely packed with very small granule neurons (smallest cells in the body), they exhibit intensly stained nuclei, and few Golgi cells are also present.
Q. What are mossy fibers?
Ans. These are afferent fibers ending in granular layer.123
 
CEREBELLUM
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  • Presence of molecular layer and granular layer and white mater.
  • Presence of Purkinje cells in Purkinje cell layer.
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CEREBRUM
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  • Presence of superficial pia mater and inner white matter.
  • Presence of stellate cells and giant pyramidal cells.
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CEREBRUM
  • Cortex is made up of gray matter.
  • Cortex consists of nerve fibers, nerve cells, neuroglia and blood vessels.
  • Neuroglia are highly branched cells that support neurons.
  • Made up of six layers of nerve cells and associated fibers.
  • A layer called superficial pia mater also present, it is a layer of pia mater overlying and covering the molecuar layer.
  • Layers from above to below.
    • Molecular layer/plexiform layer—superficial layer, well defined, mainly consists of neuroglial cells and horizontal cells of Cajal.
    • External granular layer—it consists of stellate cells and small pyramidal cells.
    • External pyramidal layer—made up of mainly medium sized pyramidal cells, few stellate cells and cells of Martinotti (small multipolar cells).
    • Internal granular layer it is a thin layer containing stellate cells which are closely packed and nerve fibers which are arranged horizontally called as outer band of Baillarger.
    • Internal pyramidal layer/ganglionic layer—consists of numerous large pyramidal cells (Betz cells) located mainly on the motor area, also contains few stellate cells and cells of Martinotti. The nerve fibers are arranged horizontally called as inner band of Baillarger.
    • Multiform layer—polymorphic cell layer, deepest layer, contains mainly fusiform cells, few stellate cells and also cells of Martinotti are present. They are mixed with nerve fiber which runs from and to the white matter beneath.
 
Applied Anatomy
  • In Huntington disease (autosomal dominant), striatal neurons are lost from cerebral cortex and putamen.
  • Ganglioglioma: Tumor affecting temporal lobe. There will be presence of a mixed population of neoplastic astrocytes and abnormal ganglion cells.
 
Viva-voce
Q. What is inner band of Baillarger?
Ans. The nerve fibers of the pyramidal layer are arranged horizontally. And this is known as inner band of Baillarger.
Q. Where are horizontal cells of Cajal present?
Ans. They are present in the molecular or plexiform layer.126