DEFINITION
- The term ‘anatomy’ is derived from a Greek word, ‘anatome’, meaning cutting up.
- Anatomical position: Descriptive terms of position are used as though the body is standing upright with the upper limbs hanging by the sides and the palms of the hands, foot, eyes directed forwards.
Subdivisions in Anatomy
- Macroscopic anatomy: study of anatomy on cadavers by dissection and observation of structures by naked eye. It can be studied by regional anatomy or systemic anatomy. Regional: head and neck, brain, thorax, abdomen and pelvis, upper limb, lower limb. Systemic: an approach in which all structures forming a system are studied together at the same time, that is, integumentary, skeletal, articular, muscular, nervous, cardiovascular, lymphatic, endocrine, digestive, respiratory, urinary, reproductive.
- Microscopic anatomy (histology): study of body structures with the help of a microscope.
- Surface anatomy: study of a deeper structure on skin surface.
- Comparative anatomy: study of changes in body that have taken place during evolution.
- Physical anthropology: study of physical characteristics of humans and their ancestors, and of variability among and within different racial groups. This knowledge helps to solve medicolegal problems of identification of individuals.
- Clinical anatomy: use of anatomical knowledge for anatomical basis, diagnosis and treatment of diseases.
- Radiological anatomy: visualization of structures and their relations with neighbouring structures inside the body by taking radiographs.
- Developmental anatomy (embryology): study of intrauterine development of an individual, which begins with fertilization and ends with birth.
TERMS OF POSITION
- Sagittal plane—a vertical imaginary plane passing anteroposteriorly through the midline of the body forming two symmetrical halves.
- Parasagittal plane—an imaginary plane passing anteroposteriorly through any part of the body parallel to median plane.
- Coronal plane—a vertical imaginary plane passing side to side at right angles to the sagittal plane.
- Transverse or horizontal plane—an imaginary plane passing parallel to the ground at right angles to vertical plane.
- Superior or cephalic—part that is nearer to the head.
- Inferior or caudal—part nearer the feet.
- Anterior (ventral)—part nearer the front of the body.
- Posterior (dorsal)—part nearer the back.
- Median—part in the middle.
- Medial—part nearer the median plane.
- Lateral—part further away from median plane.
- Superficial—part nearer the skin.
- Deep—structure away from the skin.
- Proximal—structure nearer to the trunk or root of the limb.
- Distal—structure away from the trunk or root of the limb.
TERMS OF MOVEMENT
- Movements of the trunk along the sagittal plane are known as flexion (surfaces coming closer to each other) and extension (straightening or surfaces moving away from each other).
- Movements of the trunk along the coronal plane are known as lateral flexion, in the limb they are called abduction (movements away from the median plane) and adduction (towards the median plane).
- Rotation is the term applied to the movement in which a part of the body is turned around its own longitudinal axis.
Movements | Sagittal plane | Coronal plane | Longitudinal plane |
|---|---|---|---|
Trunk | Flexion, extension | Side to side (lateral flexion) | — |
Limbs | Flexion, extension | Adduction, abduction | Medial, lateral rotation |
Thumb | Adduction, abduction | Flexion, extension | — |
CELL AND ITS ORGANELLES
Introduction
- The basic structural unit of all tissues and organs of the body are formed by the cells.
- The shape of the cell differs in many ways. It may be flattened, cubical, columnar, fusiform, stellate, pyramidal or flask shaped.
- Each cell consists of cell membrane (plasma membrane), nucleus and cytoplasm with organelles (Fig. 1.1).3
Plasma Membrane
- It forms the outer boundary of the cell and separates it from adjacent cells and external environment.
- It is a trilaminar membrane with two dense lamellae separated by a relatively clear layer.
- It forms a covering for the cell structures and helps in regulation of transporting selected substances into and out of the cell.
- In some cells the surface area of the membrane may be greatly increased by the formation of microvilli, for absorption.
- Small invaginations of the cell membranes may become detached to lie free within the cytoplasm as pinocytic vesicles. By this method, material from outside can be taken into the cell.
Nucleus
- It contains the genetic material, deoxyribonucleic acid (DNA) of the cell in the form of thin threads (chromatin) and one or more nucleoli embedded in a matrix of nucleoplasm.
- The chromatin normally exists in two forms—condensed chromatin (heterochromatin) which represents the coiled segments of chromosomes and extended chromatin (euchromatin) where segments of the chromosome thread are uncoiled.
- The nucleolus is seen as a dense region in the nucleus and contains ribonucleic acid (RNA).
Organelles
Endoplasmic Reticulum (ER)
- It consists of a system of intercommunicating membranous sacs or channels and exists in two forms—rough endoplasmic reticulum which has ribosomes attached to the outer surface and smooth endoplasmic reticulum with no ribosomes.
- They are typically arranged in flattened parallel rows. It is prominent in cells that are manufacturing proteins.
- Rough ER helps in protein synthesis and storage while smooth ER helps in lipid and steroid synthesis.
Ribosomes
- They appear as dense rounded granules lying singly or in dense clusters in the cytoplasm in the form of rosettes or spirals (polysomes) or may be attached to ER.
- They are composed of ribonucleoproteins and are sites of protein synthesis.
Golgi Apparatus
- This is a system of sacs arranged like stacks of coins and vesicles like endoplasmic reticulum but with no ribosomes attached to it.
- It is also seen prominently in secretory cells.
- They transfer materials synthesized by the ribosomes at the endoplasmic reticulum to the cell surface.
- The part of the Golgi apparatus that contains newly manufactured material breaks away from the rest and pass towards the surface of the cell as secretion granules.
Mitochondria
- They are rod-like bodies bounded by a double layered membrane.
- The outer membrane is smooth while the inner membrane is thrown into folds or cristae which project into the internal substance.
- The mitochondria provide the metabolic energy for the cell by generating ATP.
Lysosomes
- These are dense granular structures bounded by membrane and containing hydrolytic enzymes.
- Their function is to break down and digest material that has been brought into the cell by phagocytosis. The phagocytic vacuoles (phagosomes) fuse with lysosomes to enable the enzymes to act on the phagocytosed material.
Fibrils
- They are present in many cells and help to maintain the cell shape.
- The fibrils present in the muscle fibers are responsible for their contractility.
Microtubules
- They become part of mitotic spindles in dividing cells.
Centrioles
- These are a pair of short rod-shaped bodies found adjacent to the nucleus lying at right angles to each other.
- During mitosis they undergo replication and then each pair moves to opposite poles of the nucleus where they take part in the formation of mitotic spindle.
- Centrioles also give rise to cilia.
Inclusions
- These are pigments like melanin or lipofuscin, storage granules such as glycogen and fat, and secretion granules.
APPLIED ANATOMY
Terms of movement: In general the movements will be affected if the muscles are paralyzed. For example: extension at the elbow joint will be affected if the triceps brachii (action is extension at elbow joint) is paralyzed. Paralysis of triceps brachii may be due to injury to radial nerve which supplies it.