CHAPTER AT A GLANCE
- Introduction
- Basic Anatomical Terminology
- Anatomical Position
- Anatomical Planes
- Levels of Organization
- Organ Systems of Body
- Skeleton
- Cavities of the Body
- Composition of Body
- Homeostasis
INTRODUCTION
ANATOMY
Anatomy
Anatomy is the study of structure and function of the body. Aristotle (384—322 BC) was the first person to use the term “anatome”, a Greek word meaning “cutting up or taking apart”. The Latin word “dissecare” has a similar meaning.
Anatomy is one of the oldest basic medical sciences; it was first studied formally in Egypt. Human Anatomy was taught in Greece by Hippocrates (460—377 BC) who is regarded as the “Father of Medicine”.
SUBDIVISIONS OF ANATOMY
- Clinical anatomy: Correlation of anatomy with clinical signs and symptoms to arrive at a diagnosis is clinical anatomy.
- Gross anatomy: It is the study of structures of human body usually with naked eyes.
- Systemic anatomy: It is the study of the body systems, e.g. digestive system, cardiovascular system, nervous system etc.
- Regional anatomy: It is the study of structure and organization of a definitive part of the body the various parts or regions of the body studied are as follows:
- Head and neck
- Thorax
- Abdomen
- Pelvis
- Back
- Extremities—upper and lower limbs
- Functional anatomy: Study of anatomy which provides correlation between structure and function of various organs.
- Developmental anatomy: Study of prenatal and postnatal developmental changes of the human body.
- Histology and cytology: Study of various body structures organs, tissues and cells, in greater details with the help of microscope.
- Surface anatomy: Study of projection of internal body parts on the corresponding external surface area of the body. This helps in clinical correlation with normal and abnormal anatomy.
- Clinical anatomy: It emphasizes the structure and function of a part of body or the entire body in relation to the practice of medicine and other health related professions.
- Comparative anatomy: Study of structural variation between other animals and human beings. This helps to trace the sequence of events in the structural evolution of human beings.
PHYSIOLOGY
Physiology
Physiology is the branch of science that deals with various functions of living organism and the processes which regulate them.
SUBDIVISIONS OF PHYSIOLOGY
The study of functioning of each system of the body can be studies under the following subdivisions of physiology:
- Neuromuscular physiology
- Respiratory physiology
- Cardiovascular physiology
- Physiology of excretory system
- Digestion and metabolism
- Immunology
- Endocrinology
BASIC ANATOMICAL TERMINOLOGY
ANATOMICAL POSITION
All descriptions in Human Anatomy and Clinical Medicine are expressed in relation to “Anatomical Position” (Fig. 1.1).
Anatomical Position
A person in the anatomical position is standing erect (or lying supine) with the head, eyes and toes directed forward, the upper limbs by the sides with the palms facing anteriorly (Fig. 1.1).
IMPORTANCE OF ANATOMICAL POSITION
All structures of our body are described in relation to this position, irrespective to any body posture in space.
OTHER POSITIONS OF BODY
- Supine position: Person lies straight on the back with face directed upwards (recumbent position) (Fig. 1.2).
- Prone position: Person lies straight on the abdomen and face is directed downwards (Fig. 1.3).
- Lithotomy position: Person lies supine with hips and knees semiflexed, thighs abducted and feet 5strapped in position (Fig. 1.4). This position is useful in the examination of pelvic viscera of female and is commonly used during delivery of a baby.
ANATOMICAL PLANES
Anatomical descriptions are also based on four imaginary planes that pass through the body in the anatomical position. They are:
- Median
- Sagittal
- Coronal
- Horizontal
MEDIAN PLANE
This is the imaginary vertical plane passing longitudinally through the body from front to back, dividing it into right and left halves (Fig. 1.5).
SAGITTAL PLANES
These are parallel to the median plane. They are named after the sagittal suture of the skull (Fig. 1.6). The sagittal plane that passes through the median plane can be called the midsagittal plane (i.e. in center). The sagittal plane which does not pass from center but passes parallel to midsagittal plane is called parasagittal plane (Figs 1.7 and 1.8).
CORONAL PLANES
These are imaginary vertical planes passing through the body at right angles to the median plane, dividing it into anterior (front) and posterior (back) portions. These planes are named after the coronal suture of the skull, which lies in the coronal plane (Fig. 1.7).
HORIZONTAL PLANES OR TRANSVERSE PLANE
These are imaginary planes passing through the body at right angles to both the median and coronal planes (they are parallel to the “horizon”). A horizontal plane divides the body into superior (upper) and inferior (lower) parts. A horizontal plane is also referred to as the transverse plane (Figs 1.5 and 1.7).6
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TERMINOLOGY
TERMS OF RELATIONSHIP
Various terms (adjectives) are used to describe the relationship of parts of the body in the anatomical position (Fig. 1.9 and Table 1.1).
TERMS OF MOVEMENT
Various terms are used to describe the different movements of the limbs and other parts of the body. Movements take place at joints where two or more bones meet or articulate with one another.
Flexion
In this movement, two flexor surfaces come in approximation and angle of the joint is reduced (Fig. 1.10).
Extension
In this movement there is approximation of extensor surfaces whereby angle of joint increases (Fig. 1.11).
Abduction
It describes the movement away from the median plane, away from the middle finger in hand or away from the 2nd toe in foot (Fig. 1.12).
Adduction
This describes the movement towards the median plane or toward the middle finger in hand or toward the 2nd toe of foot (Fig. 1.13).
Medial Rotation
Medial rotation denotes movement toward median plane or inward rotation (Fig. 1.14).
Lateral Rotation
Lateral rotation denotes rotation away from the median plane or outward rotation (Fig. 1.15).
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Circumduction
Combined movement of flexion, extension, adduction and abduction in a circular manner is termed as circumduction.
Elevation
Raising or moving a body part toward the cephalic end is termed as elevation.
Depression
Lowering or moving a body part caudally is termed as depression.
Protrusion
Retraction
It is the backward movement from protrusion.
Pronation
It is the medial rotation of forearm so that the palm comes to face backward (Fig. 1.16).
Supination
It is the lateral rotation of forearm so that the palm comes to face anteriorly (forward) (Fig. 1.17).
Inversion of Foot
It is the movement that causes the plantar surface of foot to face inward and downward (Fig. 1.18).
Eversion of Foot
It is the movement that causes the plantar surface of foot to face laterally and downward (Fig. 1.19).
Opposition
It is a combination of abduction, medial rotation and flexion. This movement characteristically occurs in the thumb (Fig. 1.20).
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LEVELS OF ORGANIZATION AND ORGAN SYSTEMS OF BODY
LEVEL OF ORGANIZATION
For clear understanding of the body and how it functions, it is important to know the organization of the body (Fig. 1.23).
- Level 1 (chemical level): The smallest unit of a body is as an atom. Two or more atoms joined together are called as a molecule.
- Level 3 (tissue level): Groups of cells that work together to perform a particular function are called as tissue. There are four basic types of tissues in body—(i) epithelial tissue, (ii) connective tissue, (iii) muscular tissue and (iv) nervous tissue.
- Level 4 (organ level) Different types of tissues join together to form an organ. Each organ has a specific role to perform.
- Level 5 (system level): A system consists of related organs with a common function.
ORGAN SYSTEMS OF BODY
The human body has several organ systems that work interdependently and carry out specific functions. These systems influence each other and work together to maintain health, provide protection from disease, and allow for reproduction of the human species. The various structures constituting these body systems and their functions are discussed below (Figs 1.24 to 1.35).
INTEGUMENTARY SYSTEM (FIG. 1.24)
SKELETAL SYSTEM (FIG. 1.25)
MUSCULAR SYSTEM (FIG. 1.26)
NERVOUS SYSTEM (FIG. 1.27)
ENDOCRINE SYSTEM (FIG. 1.28)
URINARY SYSTEM (FIG. 1.29)
CARDIOVASCULAR SYSTEM (FIG. 1.30)
LYMPHATIC SYSTEM (FIG. 1.31)
RESPIRATORY SYSTEM (FIG. 1.32)
DIGESTIVE SYSTEM (FIG. 1.33)
FEMALE REPRODUCTIVE SYSTEM (FIG. 1.34)
MALE REPRODUCTIVE SYSTEM (FIG. 1.35)
SKELETON
The skeleton (Fig. 1.36) is the bony framework of the body. It forms the cavities and fossae that protects some structures, forms the joints and gives attachment to muscles.
The human skeleton is internal to muscles so it is described as endoskeleton. In lower animals, such as insects, the muscles are attached to the inner aspects of rigid material which also offers protection, this type is called as exoskeleton.
A detailed description of the bones and skeleton is given in Chapter 8B. Here we are considering an overview.
The skeleton is described in two parts:
- Axial skeleton: This includes bones of head (skull), vertebral column, ribs, and sternum. Hyoid bone is also the part of axial skeleton.
- Appendicular skeleton: It consists of bones of extremities, i.e. upper limb and lower limb.
AXIAL SKELETON
The axial skeleton consists of the skull, thoracic cage and vertebral column.
SKULL (FIG. 1.37)
Introduction
The skeleton of the head is called skull. It consists of the cranium and mandible. The upper part of cranium forming the brain box is termed the calvaria and the remainder of the skull forms the facial skeleton (Flowchart 1.1).
Fig. 1.36: Skeleton. Note: The green colored areas indicate appendicular skeleton (schematic representation)
Functions of Skull
- Protection of brain
- Protection of special sense organs like ears, eyes, tongue and nose
- Protection of beginning of respiratory and digestive tracts.
THORACIC CAGE (FIG. 1.38)
The thoracic cage is formed by:
- 12 thoracic vertebrae
- 12 pairs of ribs
- 1 sternum
Function of Thoracic cage
The thoracic cage protects the chief organs of respiration and circulation.
VERTEBRAL COLUMN (FIG. 1.39)
The vertebral column (spine, spinal column or back bone) is the main part of axial skeleton. It consists of 33 bones called vertebrae and the intervertebral discs between them. The vertebral column forms a strong and flexible support for the trunk; it extends from the base of the skull through the neck and trunk.
The vertebral column is made up of 33 vertebrae— 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4 coccygeal; but only 24 of them are movable (7 cervical, 12 thoracic, 5 lumbar). In adults, the 5 sacral vertebrae are fused to form the sacrum and the coccygeal vertebrae are fused to form the coccyx.
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Functions of Vertebral Column
- The vertebral column has important roles in posture, support the body weight, locomotion and protection of spinal cord and nerve roots; it also transmits the body weight to the ground through the lower limbs.
- The 24 movable vertebrae give the vertebral column considerable flexibility; the intervertebral discs between them also play an important role in movements and in absorbing shocks.
APPENDICULAR SKELETON
The appendicular skeleton consists of the shoulder girdles and upper limbs, and the pelvic girdle and lower limbs.
- The shoulder girdle is formed by the clavicle and scapula.Bones forming upper limb skeleton:
- Clavicle
- Scapula
- Humerus
- Radius
- Ulna
- 8 carpal bones—scaphoid, lunate, triquetral, pisiform, trapezium, trapezoid, capitate, hamate
- 5 metacarpals
- 14 phalanges
- The pelvic girdle is formed by the two innominate bones (help bones) and the sacrumBones forming lower limb skeleton:
- Ilium
- Ischium
- Pubis
- Femur
- Patella
- Tibia
- Fibula
- 8 tarsal bones—talus, calcaneum, navicular, cuboid and three cuneiform bones
- 5 metatarsals
- 14 phalanges
FUNCTIONS
- The bones, joints and muscles of appendicular skeleton are involved in producing voluntary movements of the body.
- It protects delicate structures like blood vessels and nerves from injury.
CAVITIES OF THE BODY
Body cavities are spaces within the body that help, protect, separate, and support internal organs. Bones, muscles, ligaments, and other structures separate the various body cavities from one another. The various body cavities are discussed below (Fig. 1.40).
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CRANIAL CAVITY
The 8 fused cranial bones form a hollow space of the head called cranial cavity. They are as follows:
- Frontal bone anteriorly
- Occipital bone posteriorly
- Sphenoid and ethmoid bone inferiorly
- Parietal bone superiorly
- Temporal bones laterally
The cranial cavity is occupied by the brain.
THORACIC CAVITY (FIG. 1.41)
The thoracic cavity is one of the major cavities of the body.
BOUNDARIES OF THORACIC CAVITY
- Anteriorly: Sternum and anterior parts of ribs and their costal cartilages
- Posteriorly: Bodies of the 12 thoracic vertebrae and posterior parts of ribs
- On each side: 12 pairs of ribs and the intercostal muscles
- Superiorly: By the structures forming the root of neck
- Inferiorly: By a muscular sheet known as diaphragm.
CONTENTS
The main organs and structures in the thoracic cavity are:
- Trachea, bronchi (2 in number) and lungs (2 in number)
- Heart, aorta superior and inferior vena cava
- Esophagus
- Lymph vessels
- Nerves
ABDOMINOPELVIC CAVITY
The abdominopelvic cavity is the other major cavity of the body. It extends from the diaphragm to the groin. It is encircled by the muscular wall of the abdomen, and bones and muscles of the pelvis.
The abdominopelvic cavity can be divided into two regions:
- Abdominal cavity
- Pelvic cavity
ABDOMINAL CAVITY
It is the largest cavity in the body.
For purposes of description, the abdominal cavity is divided into nine regions by the two lateral vertical planes (mid inguinal or midclavicular) and 2 horizontal planes (transpyloric plane and transtubercular plane) (Fig. 1.42).
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Transpyloric Plane of Addison
Passes midway between the suprasternal notch and pubic symphysis, roughly a hand's breadth below xiphisternal joint. It passes through the tips of the 9th costal cartilages anteriorly and through the body of L1 vertebra posteriorly.
Transtubercular Plane
Transtubercular plane passes through the iliac tubercles on the iliac crests. It passes through the body of L5 vertebra.
Midclavicular Lines
The midclavicular lines or planes extend from the midpoint of clavicle to the midinguinal point (midpoint of a line joining anterior superior iliac spine and pubic symphysis).
Nine Regions of Abdomen (Fig. 1.42)
- Epigastric or epigastrium
- Right hypochondrium
- Left hypochondrium
- Umbilical
- Right lumbar
- Left lumbar
- Suprapubic or hypogastrium
- Right iliac fossa or right inguinal region
- Left iliac fossa or left inguinal region.
These regions are helpful clinically for describing the location of pain, site and size of a swelling, site of an incision or for locating the viscera (e.g. liver in the right hypochondrium, urinary bladder in the hypogastrium, etc).
QUADRANTS OF THE ABDOMEN
For simplicity, clinicians routinely divide the abdomen into 4 quadrants, right and left upper and lower quadrants. The median and transumbilical planes are used to divide the abdomen into these quadrants.
Boundaries of Abdominal Cavity
Its boundaries are:
- Superiorly: The diaphragms, which separates it from thoracic cavity
- Inferiorly: It is continuous with pelvic cavity
- Anteriorly: Anterior abdominal wall
- Posteriorly: Lumbar vertebra and posterior abdominal wall
- Laterally: Muscles of abdominal wall and lower ribs
The main organs and structures in the abdominal cavity.
- Stomach
- Small intestine
- Most of the large intestine
- Liver
- Gallbladder and bile ducts
- Pancreas
- Spleen
- Kidneys (2 in number) and the upper part of the ureters
- Adrenal (suprarenal) glands (2 in number)
- Numerous blood vessels, lymph vessels, nerves, and lymph nodes.
PELVIC CAVITY
The pelvic cavity extends from the lower end of the abdominal cavity
Boundaries of Pelvic Cavity (Fig. 1.45)
It boundries are:
- Inferiorly: Pelvic floor
- Anteriorly: Pubic bones
- Posteriorly: Sacrum and coccyx
- Laterally: Hip bones (innominate bones)
Contents
The main organs and structures in pelvic cavity are:
- Urinary bladder
- Lower parts of the ureters
- Urethra
- Lower part of colon including sigmoid colon, rectum and anal canal
- In the male, prostate gland, seminal vesicles, spermatic cords, vas deferens, ejaculatory ducts, and urethra (Fig. 1.45)
Fig. 1.45: Male reproductive organs and other structures in the pelvic cavity (schematic representation)
Fig. 1.46: Female reproductive organs and other structures in the pelvic cavity (schematic representation)
COMPOSITION OF BODY
In average adults, 60% of total body weight is water, 8% is protein and related substances, 15% is fat and 7% is minerals.
The body water is divided into two parts:
- Intracellular fluid (ICF): It is the fluid contained within the cells. It forms two-third of total body water and 40% total body weight.
- Extracellular fluid (ECF): It forms one-third of total body water and 20% of total body weight. It is further divided into two components:
- Intravascular fluid: It is 25% of ECF and forms 5% of total body weight. Plasma along with various cellular elements forms blood which circulates in the vascular system and is called as intravascular system.
- Extravascular fluid: It is 75% of ECF and forms 15% of total body weight. This fluid lies outside the blood vessels and bathes all the cells except red blood cells and is found in pleural cavity, pericardial cavity and around joints (Flowchart 1.2).
The normal cells function depends on the composition of interstitial fluid. It constitutes the internal environment of the body or milieu interieur. The internal environment of the body is kept constant by multiple regulatory factors. This is called homeostasis.
HOMEOSTASIS
The word “homeostasis” was coined by Walter B Canon.
Homeostasis
The word “homeostasis” means a constant internal environment in the body which remains within certain physiological range. The concept of homeostasis forms the basis of physiology because it explains why various physiological functions are to be maintained within a normal range and in case if any function deviates from this range how it is brought back to normal.
COMPONENTS OF HOMEOSTATIC SYSTEM
The homeostatic system is a self-regulating mechanism that occurs in a cyclical pattern. There are three components of homeostatic system (Flowchart 1.3):
- Receptors: These recognize any deviation from normal level of a physiological parameter and provide feedback to control center .
- Control center: This receives the information about variation in the physiological parameters from receptors and activates the effector system.
MECHANISM OF ACTION OF HOMEOSTATIC SYSTEM
The homeostatic system acts through feedback mechanisms. Feedback is a process in which some proportion of the output signal of a system is fed (passed) back to the input. There are two types of feedback mechanisms:
- Negative feedback mechanism
- Positive feedback mechanism
Negative Feedback (Flowchart 1.4)
Negative feedback is the one, to which the system reacts in such a way so, as to arrest the change or reverse the direction of change.
After receiving a message, the effectors send the negative feedback signals back to the system. Now the system stabilizes its own function and makes an attempt to maintain homeostasis.
Most of the homeostatic mechanisms in the body function through negative feedback, for example, adrenocorticotropic hormone (ACTH) and cortisol secretion.
Flowchart 1.4: Negative feedback mechanism
Abbreviation: ACTH, adrenocorticotropic hormone; ⊕, stimulates; ⊖, inhibits
ACTH released from anterior pituitary stimulates cortisol secretion from adrenal cortex. The increase in blood cortisol levels inhibit secretion of ACTH from anterior pituitary so that cortisol secretion from adrenal cortex decreases. On the other hand low cortisol levels induce pituitary gland to secrete ACTH to stimulate cortisol secretion to maintain normal levels.
Positive Feedback (Flowchart 1.5)
Positive feedback is the one, to which the system reacts in such a way as to increase the intensity of the change in the same direction. In other words, in positive feedback, the response reinforces the stimulus rather than decreasing or removing it. Positive feedback systems are less common and occur in both physiological and pathological state.
This is very useful in life processes. Examples of positive feedback system are:
- Ovulation
- Parturition
- Clotting of blood
Ovulation
Follicle-stimulating hormone (FSH) secreted by anterior pituitary stimulates secretion of oestrogen from the ovary. The increased blood oestrogen levels stimulate luteinizing hormone (LH) surge. This LH surge triggers release of ovum from the Graafian follicle. This is a useful physiological process for the perpetuation of the species.
Flowchart 1.5: Positive feedback mechanism
Abbreviations: FSH, follicle-stimulating hormone; LH, luteinizing hormone
Applied Physiology
DISRUPTION OF HOMEOSTASIS DISEASE
The internal environment should remain constant for the optimal cellular activity.
Whenever there is a change in the internal environment (e.g. rise in ECF volume, body temperature, etc.), the cellular activity is affected. This is immediately brought back to normal level by various mechanisms combinedly called homeostatic mechanisms.
If these mechanisms fail to maintain a constant internal environment then disease develops. It may finally lead to death of the organism.
The commonly used terms to describe the disease are summarized in Flowchart 1.6 and discussed in brief below.
- Disorder: Any abnormaliy of structure or function.
- Disease: A disease is a definite abnormal pathological condition that affects the body of an organism. It is often construed as a medical condition associated with specific symptoms and signs.
- Etiology: The word is derived from the Greek word “aitiologia”, i.e. “aitia” meaning “cause” and “logia” meaning “giving a reason for”. It is defined as the cause of the disease. The three most common causes for most of the diseases are the 3 T' s:
- T-Trauma
- T-Tumor
- T-Tuberculosis (infection)
- Pathogenesis: The word is derived from the Greek word “pathos” which means “disease” and “genesis” meaning “creation”. The pathogenesis of a disease is defined as the mechanism that causes the disease. The term can also describe the origin and development of the disease, and whether it is acute chronic or recurrent. Acute disease is a disease with a rapid onset and/or a short course. Chronic, i.e. which is slow in onset and a prolonged course of illness that do not resolve spontaneously until treated, recurrent disease, i.e. those disease whose signs and symptoms reappear after remission.
- Symptoms: Subjective changes in the body functions that are not apparent to the observer but felt by the patient.
- Signs: Objective changes in the body that are visible to the observer.
- Inspection: The word is derived from Latin word “Inspectio” meaning “the act of beholding”. It is the thorough and unhurried visualization of the patient.
- Palpation: The method by which a healthcare practitioner, diagnoses a disease by using both of his hands by feeling the organ in the body to determine its size, shape, firmness, or location. Typically used for thoracic and abdominal examinations, but can also be used to diagnose edema and to measure the pulse.
- Percussion: It is the method of tapping on a surface to determine the underlying structure. It is used in clinical examinations to assess the condition of the thorax or abdomen. There are four types of percussion sounds—resonant, hyper-resonant, stony dull or dull. A dull sound indicates the presence of a solid mass under the surface. A more resonant sound indicates hollow, air-containing structures.
- Auscultation: Derived from the Latin verb “auscultare” that means “to listen”. It is used for listening to the internal sounds of the body, usually using a stethoscope. The sound heard on auscultation are - breath sounds, heart sounds and bowel sounds.
- Complications: Complication is an unfavorable evolution of a disease, a health condition or a therapy. The disease can become worse in its severity or show new pathological changes or become widespread throughout the body or affect other organ systems.
- Prognosis: The word is derived from Greek word “progignoskein” meaning “fore-knowing or foreseeing”. It is defined as a medical term for predicting the likely outcome of a disease.
- Acute disease: A disease condition characterized by a relatively sudden onset of symptoms that are usually severe.
- Chronic disease: A disease condition which is persistent or lasts for a longer time.
- Nosocomial disease: The term “nosocomial” comes from two Greek words “nosis” meaning “disease” + “komeiion” meaning “to take care of”. Hence, “nosocomial” should apply to any disease contracted by a patient while under medical care. However, this term is now synonymous with hospital-acquired infection.
- Syndrome: A group of symptoms that occur together and are characteristic of a specific disorder, disease or condition.
