ANATOMY
It is a study of body structures and their relation to other organs in the body. For example, to describe an organ like stomach, we have to know about its shape, the part of the body where it is situated, its blood supply, nerve supply and also about the organs situated—infront, behind, above, below and on its sides.
PHYSIOLOGY
It is a study of functioning of normal organs in the body. By studying physiology, we will know the purpose of each organ in the body. To make it simple for understanding, we can say that anatomy is like hardware and physiology is like software in a computer like body.
The body parts are studied by different methods. If the organs are studied regionwise, then it is called ‘regional anatomy’. When we take head and neck as one region, we study the anatomy of structures situated only in head and neck. Another way to study anatomy is by learning about all the organs belonging to a particular system. This type of study is known as ‘systemic anatomy’. For example, all the organs of the body concerned with digestion, absorption and excretion of undigested food is grouped under the ‘alimentary system’. Similarly, we have other systems like the respiratory, cardiovascular, renal and many more.
PATHOLOGY
This branch of science deals with understanding of various disease processes, their causative factors and their effect on various organs. 2We study not only the anatomical changes but also the chemical changes in the body by various laboratory tests.
In addition, X-ray investigations are used in the diagnosis of diseases. In treating diseases, there are mainly two branches—medical and surgical. Both medicine and surgery have many subspecialities.
CELL
A cell is the basic structural and functional unit in the body. When cells of the same type and having a similar function are grouped together, they form ‘Tissue’. Aggregation of various types of tissues constitutes an organ.
We have seen in nature, some unicellular organisms but man is multicellular. In humans, like many other multicellular organisms, the cells belong to a particular group will have a special function of their own. Though the basic structure of different cells in the body is the same to a large extent, they can only perform some specialized functions. Whereas, a unicellular animal like amoeba can perform all the basic functions of a fully-grown multicellular animal.
A typical cell (Fig. 1.1) has a cell membrane, which encloses all the contents of the cell.
The cell membrane, also known as 3plasma membrane, is made up of carbohydrates, proteins, and fats. The phospholipids, which are the fatty substances, are the most important components of cell membrane. They prevent the cell membrane from mixing with water, thus, maintaining its integrity. The cell membrane itself acts as a selective sleeve for allowing certain nutrients and gases between the intra-and the extracellular fluids. The contents of the cells are called ‘cytosol’.
Mitochondria: The mitochondria are shaped like sausages. They are the ‘powerhouse’ of the cell. Very active cells will have more number of mitochondria. They help in catabolism involving aerobic respiration, a reaction requiring oxygen. During the process of chemical reaction, carbon dioxide is released.
Endoplasmic reticulum: These are seen as interconnecting canals in the cell. They are helpful in detoxification of certain drugs. They also help in the synthesis of steroid hormones, lipids and enzymes (Fig. 1.2).
Ribosome: They are made up of RNA. They are helpful in the synthesis of proteins that are used by the cells or by any other parts of the body.
Golgi apparatus: They are mainly concerned with secretory activity.
Centrosome: It plays an important role during cell division.
Nucleus: Except mature red blood cells, all the cells in the body have a nucleus. A skeletal muscle fiber may have more than one nucleus. 4The outer covering of the nucleus is the nuclear membrane, which has pores through which materials can exchange between inside and outside the nucleus. Contents of the cell, excluding nucleus, is called cytoplasm. The nucleus contains chromosomes that are important for the activities of the cell and they also determine the hereditary characteristics of an individual. Normally, these chromosomes, which are made up of deoxyribonucleic acid are arranged as a fine network known as chromatin. The chromosomes become clearly visible at the time of cell division.
It is a common observation that the children look like and many times exhibit the behavior of their parents or grandparents. These features are transmitted by the parents to their children through ‘genes’, which are situated on chromosomes. Genes carry coded information about the ancestors. Every species has a fixed number of chromosomes. Human beings have 23 pairs (total 46) of chromosomes in each nucleus. It is said that if all the chromosomes in a nucleus are lined together, they measure to about 180 cms in length and if the chromosomes of all the nuclei in the body are lined lengthwise, the measurement comes to about 27 billion km. They are of very lightweight. If chromosomes are arranged lengthwise between the earth and the sun, the total weight of these chromosomes comes to about 0.5 gms.
The cells divide and multiply by a process known as ‘mitosis’. During cell division, the centrosome becomes active. The chromosomes in the nucleus become clearly visible and divide in the middle. The divided chromosomes move toward the edge of the cell. At this time, the cell divides in the middle, giving rise to two daughter cells. Each new cell contains 23 pairs of chromosomes, like parent cell.
Some cells in the body divide rapidly and there is a constant process of new cell production and removal of old cells. The cells, which are replaced at short intervals, are called ‘labile cells’. They include epithelial cells. Some cells like those seen in liver and kidney, are replaced less frequently they are called ‘stable cells’. This type of replacement of cells is not seen in nerve cells, skeletal and cardiac muscle cells. These cells are called ‘permanent cells’.
The gametes (ova and spermatozoa) divide by a process known as ‘meiosis’. Here, the daughter cells will have only 23 chromosomes. When fertilization takes place, the fertilized ovum will have 23 pairs of chromosomes.
5Cell extensions: Some cells in the body contain hair like extensions, which are called cilia. The spermatozoa contain larger projections called ‘flagella’, which help in their movement.
TISSUE
The word ‘tissue’ is used to describe a collection of cells, specialized to carry out a particular function. There are four main types of tissues:
- Epithelial tissue
- Connective tissue
- Muscle tissue
- Nerve tissue.
The muscle and nerve tissue will be described in their appropriate chapters.
Epithelial Tissue (Figs 1.3A to D)
These cells cover the body surface and also line the inside of the body cavities and hallow organs. Depending on their location, they perform different kinds of functions. Their main function is to protect the underlying organs. They take part in secretion, excretion, and in certain places they allow free movement of the organs by reducing friction. They are arranged together on a firm basement membrane. Basically, epithelial tissue is classified as simple and compound type.
Simple epithelium: It has a single layer of cells. There are different varieties of simple epithelia, classified depending on the shape and function of the cells. The different varieties are:
- Squamous type: They are also called pavement type, as they look like stones arranged on a pavement. It consists of single layer of flat cells. Diffusion process is easy across this type of epithelial tissue.
- Columnar type: This type is seen in gastrointestinal tract. Some of these cells secrete substance necessary for digestion of food, some secrete mucus, and some are involved in absorption of digested food. This type of tissue is also seen in glands and genitourinary tract. The mucus secreting cells are called ‘goblet cells’.
- Cuboidal tissue: These cells are short and cuboidal in shape. They are seen in renal tubules. Some of these cells secrete, some absorb and some take part in excretory activity.
- Ciliated type: Many of these epithelia have columnar type cells with cilia at their free edge. When all the cilia move at a time in one direction, it looks like movement of grass in a field when the wind blows. This type of epithelium is seen in respiratory tract, and uterine tube. They propel the mucus towards the throat in respiratory passages and help to move the ovum towards uterine cavity in the uterine tube.
Compound epithelium: This type of epithelium, which is also known as stratified type, has more than one layer of cells. The deeper layer has freshly formed cells. These cells gradually move towards the periphery. Basement membrane is not usually seen. This type of epithelium is seen in places like skin, mouth, pharynx, urethra, anal canal, vagina and conjunctiva. The superficial layer of the epithelium, which covers dry surfaces like skin contain mostly dead cells. They contain a fibrous protein called ‘keratin’, which gives a waterproof quality to the skin. This variety of epithelium is called keratinized epithelium. However, the epithelia of wet surfaces like conjunctiva, pharynx and other similar places are nonkeratinized.
Type of compound epithelium is seen in places like urinary bladder, is slightly different type and is called transitional type. Here, the epithelium allows the bladder to stretch when urine accumulates.
Connective Tissue
They are seen in many parts of the body. Their main function is to protect the body organs. They also help to separate each organs and make partitions in the organs. It acts mainly as packing and insulating material. There are many types of connective tissue. They are:
Areolar tissue: They are distributed all over the body. They are seen in more abundance under the skin, in the glands, muscles, nerves and blood vessels. The fibers are loosely woven in the intercellular fluid. Intercellular fluid, which forms the ground substance, is also referred to as matrix.
Adipose tissue: This tissue consists of fat cells, which are also known as adipocytes. It is seen in many parts of the body, especially in the subcutaneous space, around the kidneys and eyeballs. Adipose tissue normally stores fat along with water.
8Dense connective tissue: Seen in structures like ligaments (connecting the bones), periosteum (outer covering of bones) tendons and dura matter.
Elastic tissue: These connective tissue fibers are capable of shortening and lengthening. They are seen in places like trachea and arterial wall.
Blood: Blood is also a form of connective tissue.
Lymphoid tissue: The matrix here is semisolid which contains branching reticular fibers, white blood cells (monocytes and lymphocytes) and reticulocytes, which are nothing but immature red blood cells.
Cartilage and bone belong to connective tissue. They will be described in the chapter dealing with the ‘Skeletal System’.
MEMBRANES
Knowledge of epithelium and connective tissue is necessary to understand ‘membranes’. A layer of epithelial tissue in the form of a sheet along with its connective tissue support forms a membrane. These membranes line the body cavities. Some of the membranes are:
Mucous membrane: This type is seen in the organs of alimentary, respiratory and urinary systems. They have a variety of functions to play. They take part in secretion, excretion and absorption depending upon the part of the body they are covering. Special cells are called goblet cells, secrete mucus.
Serous membrane: The pleura covering the lungs, peritoneum covering the abdominal organs and the pericardium covering the heart belong to this type of membrane. These membranes are double layered connective tissue lined inside by simple layer of squamous epithelium. The layer, which is in contact with the organs intimately, is called ‘visceral layer’ and the one, which is away from the viscera, is called ‘parietal layer’. Normally, a small quantity of serous fluid is present between these two layers. This liquid acts as a lubricant, so that the organs enclosed by them can move freely without any friction.
Synovial membrane: This type of membrane is seen in synovial joints. Synovial membranes also surround the tendons. 9The lubricating fluid inside the membrane is called ‘synovial fluid’. The synovial fluid also supplies nutrients to the cartilages.
ANATOMICAL DESCRIPTIVE TERMS
While describing the anatomical position of an organ, standard and universally accepted terms have to be used. These terms are used with reference to the ‘Anatomical position’ (Fig. 1.4). An anatomical position is one, where a person is standing errect, looking forward with his hands hanging by his sides, the palms looking forward and the feet are placed in such a way that the toes are also directed forward. An imaginary line passing in the sagittal plane is used to divide the body into right and left halves. This line is also known as midline or median line.
10The words anterior and posterior are used to describe the front and back parts, respectively. For example, stomach is anterior to the vertebral column and abdominal aorta.
The words medial and lateral are used to describe the relationship of two structures placed side by side. The structure close to the midline is ‘medial’ while the structure away from the midline is ‘lateral’. For example, in the forearm, ulna is placed medially and radius is placed laterally. Similarly, we also use terms like ‘anterio- medial’ ‘posteriomedial’ to describe exact position of certain organs.
The terms proximal and distal are used to describe the relationship between two organs, which are situated away from each other in vertical direction. Organ, which is nearer to the head, is proximal and the one away from the head is distal. For example, shoulder joint is proximal to the elbow and elbow is distal to the shoulder but proximal to the wrist joint. Similarly, while describing the movements at joints certain universally accepted terms are used.
Abduction and adduction: Any movement away from the midline is abduction and movement towards the midline is adduction.
Flexion and extension: Bending movement in a joint where the proximal and distal bones of the joints come close together is known as ‘flexion’ and the movement where the bones move away from each other causing straightening of the joint is called ‘extension’.
Rotations: In the anatomical position, an imaginary line passing through the long axis of the limb is used to describe rotations. Depending upon the movement of the part of the body distal to the joints, rotations may be medial or lateral.
Supination and pronation: These movements, though seen in both hands and feet, can be demonstrated best in the hands. These movements take place at the radioulnar joint. They are tested in the anatomical position, with the shoulder joint kept stable. The rotation movement at the radioulnar joint, which causes the palm to look back, is called ‘pronation’ and the movement, which causes the palm to look forward, is called ‘supination’. Supination and pronation movements can also be demonstrated when the elbow is flexed at 90°, when the palm looks down, it is pronation and when the palm looks up, it is supination.
11Inversion and eversion: These movements are seen in the foot. During inversion, the sole of the foot is turned medially while in eversion; the sole of the foot is turned laterally.
Circumduction: This movement involves combination of all the movement at a joint.
PHILOSOPHICAL BACKGROUND
The scriptures not only deal with the universe and the creator but also tell us about our body and the way, the atman (individual soul) works in our body. Mandukya Upanishad says that the atman has to deal with seven different parts of the body (sapangah). Explanation about, what exactly, these seven parts of the body differs among different commentators. This Upanishad, further says that the atman acts mainly through nineteen outlets (ekonavimasati-mukah), which include five organs of senses (Jnanendriyas—eyes, nose, ear, tongue and skin), five work organs (karmendriyas—speech, hands, feet and two outlets at the lower part of the abdomen), five pranas (parts of vital energy—prana, apana, samana, vyana and udana) and four parts of the mind (mind, intelligence, ahankara and chitta).
In philosophy, we try to learn the force behind the working of the body organs. As ‘Kenopanishad’ says, “your eyes are unable to see it but your eyes are seeing because of it. Your mind cannot think about it but your mind is thinking because of it. This power inside you is “Brahman”. As per Kathopanishad, only a person with a sense of detachment and discriminative power will be able to look inside and realize the self. Upanishads also go one step beyond our scientific thinking. For example, it is very easy to observe and explain why an apple fell from a tree. But a philosopher will try to understand how the apple climbed the tree. Science tells us that we see through the eyes but the scriptures explain why the eye sees.
The scripture also talk about three bodies: Gross body, subtle body and the causal body. The body, which our anatomy and physiology books describe, includes: All body organs, their microscopic structures and their biochemistry. All these are considered as gross body by Upanishads.
The atman takes up its individual identity as jivatman by its association with five great elements (space, air, fire, water and 12earth). Subtle forms of these five great elements, five sense organs and work organs, vital air, the mind and the bundle of karmas constitute our subtle body. This body is referred to as “Me or I”. It is this subtle body, which goes out when a person dies to take up a new gross body.
The causal body is also called “maya” or “ignorance”. Not realizing self is ignorance. A person who has realized self can get liberated from the combination of atman and jiva. Once the jivatman gets rid of all its components and become pure atman, he is free from further births.
The Upanishads also teach us about the gross body and the atman. “Me and I” refer only to the jivatman. The gross body is only “mine”.
There are several millions of cells in the body. They are all ‘living cells’, capable of dividing into daughter cells. However, they are not individual living entities. They are living because of the presence of ‘jivatman’ in the body. The male and female genders and all the diseases, belong only to the gross body but not to the jivatman. The actions of jivatman through gross body are recorded as ‘karmas’.
The scriptures tell us that our body has two separate components. One is our body and other is the vital force (individual soul or jivatma), which keeps our body alive. The body is alive as long as the soul remains inside and once it leaves, the body becomes lifeless. The ultimate goal of the human life is to understand and realize the real nature of this self. The Upanishads are using different methodologies to tell us about self. One of the methods used in Taittiriya Upanishad is pancha kosha viveka or knowledge of five sheaths. The gross body is considered to be the first sheath ‘Annamayakosha’, which is essentially made up of food, we eat. This cannot be the self since, it keeps on changing all the times. Next one is subtle layer ‘Pranamaya kosha’ made up of prana or vital air. Even prana changes and cannot be considered as the soul. Next is the mind, ‘Manomaya kosha’. Next comes ‘Vijnanamaya kosha’ or the sheath of intelligence. Mind and the intelligence also cannot be considered as the soul, as they keep on changing. Finally, the jivatmman that is illuminating the body (referred to as ‘Anandamaya kosha’) is controlling the whole body and keeping it alive. This is considered as individual soul.