HUMAN PHYSIOLOGY 

SYSTEMS IN HUMAN BODY

1. The Skeleton or Bony SystemThe human body is supported on an internal skeleton consisting of 20(5 long, short and irregular bones. These are joined together in several modes. The main functions of the skeleton are:(1)   to stiffen the body (2) to provide levers upon which muscles of the. body work (3) to give shape to the body and (4) to protect the internal organs.

 2. Muscular SystemThe muscles of the body are attached to the bones of the walls of the organs and affect the movements of the body. Muscles are thick at the centre and thin at the ends. In the human body, there are over 300 muscles. These are of two types:(i)Voluntary Muscles: These are under our control, such as muscles of head, legs, neck, etc. These cause the external movements of the body. These are situated on the bones.(ii) Involuntary Muscles: These are not under our will, such as muscles of lungs, heart, kidneys, etc. These cause the internal movements of the body. These are situated on the wall of the internal organs. 

3. Circulatory SystemThis consists of heart and blood vessels which, by carrying blood to all parts of the body, supply nourishment to the various tissues; and by bringing it back, remove the waste products of the body. The heart, by contraction, pumps the blood into vessels called arteries which carry the blood to every tissue. In the substance of every organ, the arteries divide into a very fine network of extremely small hair-like tubes called capillaries. Through the walls of capillaries, the organs receive nourishment. The capillaries reunite and pour the blood into veins which carry the blood containing waste products back to the heart.The impure blood gathers from all parts of the body on the right auricle of the heart, from where it is sent to lungs where it is purified by the oxygen breathed in. The purified blood then goes to the left-hand side of heart. Finally, then, the blood is back from where it started. The process goes on again and again till our last breath. Functions of the HeartIt is clear from the above discussion that the functions of the heart are three-fold: (i) to supply pure blood to all parts of the body;(ii) to collect impure blood from the organs Of the body; and(iii) to pump impure blood into lungs for purification.Functions of the LungsThe main functions of the lungs are: (i) to purify the blood, i.e., to separate the carbon dioxide and water vapours from blood; and(ii) to give oxygen to the blood.

4. Digestive SystemIt consists of a very long (31 feet) tube, known as alimentary canal. Its main parts are mouth, gullet, stomach, small intestines and large intestines. The digestive fluids such as saliva, gastric juice, bile and intestinal juices are poured into the canal by the neighbouring glands and walls of the tubes itself while the food is passing through the various regions. The object of the digestion is to convert the food into a fluid state so that it is capable of being absorbed by the blood. SalivaIt is secreted by the three pairs of salivary glands situated in the mouth. It is alkaline in reaction and contains a ferment which converts starch into sugar.Gastric JuiceIt is secreted by gastric glands in the stomach. It converts insoluble proteins into soluble peptones and coagulates milk.StomachIts main functions are: (0 to stop the action of saliva, a juice which converts starch into sugar;to change insoluble proteins into soluble peptones; and to coagulate milk.Bile FluidIt is a greenish alkaline fluid poured into duodenum (part of small intestines) by the liver through the gall bladder. It is antiseptic and emulsifies fats and food.Pancreatic JuiceIt is secreted by pancreas which are situated in the bend of duodenum. It secretes insulin which acts upon the carbohydrates, the fats and proteins. It digests food and keeps sugar balance in the body.LiverIt is dark red in colour and weighs about 40 to 60 ounces. It is the largest gland in the body. It helps in digesting food. Its main functions are:(i) to act as a store of digested sugar for use when required in the body;(ii) to help in digesting food;(iii) to separate nitrogenous waste; and(iv) to kill poisons produced in-the body.It is the biggest organ of the body.

5.Respiratory SystemThe respiratory system in the human body is an apparatus to get oxygen into the blood and carbon dioxide out of it. The system consists of two lungs and the passages leading to lungs, a nose, wind pipe, etc. When the diaphragm (in the body) contracts, a large cavity is formed in the throat. In order to fill up that cavity, fresh air from the nostrils is sucked in and this is called respiration. Now the diaphragm comes to its real form and cavity becomes smaller and we exhale the impure air and expiration takes place.

6.Excretory SystemKidneys and skin are the chief organs of excretion. They throw out the waste products of the body in the form of urine and sweat, respectively.Kidneys: They are two in number. They filter the nitrogenous wastes of the body fron\ the blood and throw them out in the form of urine. Urine filtered by kidneys is stored in the bladder.Skin: It is the outer covering of the body. Its main functions are:(i) to protect the inner organs;(ii) to regulate the temperature of the body;(«/) to act as the organ of touch;to throw out the nitrogenous waste; andto give shape to the body.

7. Nervous SystemThe system consists of nerves, brain and spinal cord. They control the working of various organs of the body. The brain controls thought, memory, intelligence, etc. The spinal cord controls the reflex action and works when brain is asleep. This part is called Autonomic Nervous System.Cerebrum: It is the seat of memory coordination and intelligence in brain. It is the largest part of brain.

8. Reproductive System There are certain organs in the body which are set apart for the reproduction of the species. They are of different types in males and females.