Man is an active being. In order to carry out his activity, he has to get energy; this energy is secured by the food he takes. Food is converted into energy, through digestion and assimilation. This process is carried out by the digestive system.
The digestive system consists of the following:
(i) The mouth, in which are the teeth, tongue and salivary glands;
(ii) The alimentary canal and certain glands in its different regions;
Function of Digestive System:
The human digestive system serves the following functions:
(a) At first it helps in taking up the food by the mouth;
(b) It helps in digestion of food;
(c) It secretes various digestive juices which help in digestion;
(d) It helps in absorption of water, salts, vitamins and end products of digestion;
(e) It helps in excretion of heavy metals, certain alkaloids etc.
(f) The movements of alimentary canal facilitate admixture of food with digestive juices, to propel food onwards, to help blood circulation through the intestinal wall. Defecation is also due to the movements of large intestine;
(g) The alimentary canal takes part in the regulation of blood sugar;
(h) It also maintains the water balance. The phenomenon of thirst is an important function of the digestive tract by which the fluid balance of the body is maintained.
The Structure and Function of Digestive Organs:
Teeth play a very vital role in digestive system. Teeth hive three parts; the crown which is outside the gums, the root is buried in the bones of the jaws the neck is the thinnest part and cuts the crown and the root of the teeth.
The crown is covered with enamel which is very brittle The teeth however, are made chiefly of a substance called dentine, which is hard like bone, but different in structure- Towards inside, there is a hollow portion which filled with a substance called pulp, in which a large number of small branches of blood vessels- an nerves are present, which enter into the tip of the root.
This accounts to the severe pain felt in decaying teeth. Teething takes place twice in the life of an individual. Teeth begin to appear in infants when they are about six months old The first set, called the temporary or milk teeth are twenty in number and grow almost all by the age of two years The second set, called the permanent teeth, are thirty two in number begins to appear at the age of 6 years and almost all have come out by the age of 12 years except the last molar or wisdom tooth which appears at the of 25 to 30 years.
The front teeth, four in number in each jaw, are called incisors or cutting teeth. Next to them come the canines which are narrow and blunt pointed. There is one canine tooth on either side of the incisors ill both jaws.
Next to the canines on either side and in both jaws are two bicuspids or pre-molars; and, lastly, in growth up people are three molars or grinders, also on either side in both jaws, situated at the back As a whole teeth help in mastication of food and as a result of which the solid particles are broken into smaller pieces and which are easily digested in the alimentary canal. The teeth also help in the secretion of salivary juices.
The small bodies which projects from the surface of the tongue, and which are best seen at the back, are called pillar in the papillae small taste buds are present, the front and side of the tongue among them which are in the front and side of the of the tongue are for sweet substances while those at the back are for letter. The tongue helps in the act of chewing and swallowing it is also essential for speech By the secretion of mucus and serous fluid it keeps the mouth moist.
The Salivary Glands:
Here are three pairs of salivary glands present on either side or open into the oral cavity by a single duct or by several fine ducts. The glands are situated at the angle of the lower jaw, .under the jaw, and under the tongue. The cells of the glands secrete the saliva, which are thin and watery. The chief constituent of saliva is ferment called ptyalin; which converts starch into grape sugar. The saliva also dissolves solid bodies, such as sugar and salt and helps us to swallow our food. Over twenty ounces of saliva are secreted daily.
The Ocsophagus or Food Pipe:
The ocsophagus is about 10 inches in length and situated behind the wind pipe, which is protected against the entrance of food by a covering or lid called the epiglottis, which closes when the food is being swallowed. Our food does not drop into our stomach suddenly. It is carried down the gullet by a series of movements caused by the action of the muscles in the walls of the gullet. It is by this action that water and food can be swallowed by people while standing on their heads.
The ocsophagus leads into the stomach which is 'J' shaped and situated in the upper part of the abdomen just below the diaphragm, a little towards the left. It can be divided into three parts—the funds, the body and the pylorus.
The entrance to the stomach is known as the cardiac and the outlet as the pyloric orifice or opening is about 12 inches long. The interior of the stomach is lined with minute glands, called peptic gonads, which secrete a liquid called the gastric juice.
The gastric juice among other ingredients contains hydrochloric acid and substances called pepsin and rennin, both of which art ferments.
Digestion is carried out chiefly in the stomach by means of these substances. The movements of the stomach help in the proper mixing of food with the digestive juices and also help to propel the food into the duodenum. The hydrochloric acid acts as an antiseptic against swilled bacteria. With the help of gastric juice, stomach digests protein up to peptone stage. It also digests fats to some extent with gastric lipase.
The rennin coagulates milk and it turns into curds. When food is digested in the stomach it is converted into a substance called chime; which has a sour smell and taste. Small quantities of water, salt, alcohol and glucose are absorbed from the stomach.
The intestines are divided into the small and large intestine respectively. The small intestine comes first, and is about 18 feet, while the large intestine is only 5 to 6 feet in length. The first portion of the small intestine is called the duodenum, which is only about 10 inches long.
The duodenum is 'C' shaped and below it head of the pancreas is situated. Both the bile duct and pancreatic duct open into the duodenum. The duodenum has numerous small glands in its walls, which secrete fluid resembling saliva. This fluid ' helps to digest the starchy food which escapes from the action of the saliva in the mouth and stomach.
The parts of small intestines have numerous small structures called villa containing blood-vessels and also small glands which secrete the intestinal juice. The large area of the small intestine helps in] the absorption of the digested food into the blood.
The large intestine begins in the right of the abdomen and goes up across the upper part of the abdomen and ultimately curves down towards the left. The small intestine opens in it at the right at the joint there is a 3 inches long appendix which is of no use. There is no villa in the large intestine, but its walls have the capacity to absorb water from the waste and the waste is moved forward by the muscular movement and expelled out as defecation.
This is also a part of the digestive system. It is situated on the right side of the stomach and slightly below the stomach. It is a narrow long gland which is wide on its right and narrow on the left. It is 6 to 7 inches long and 2 inches wide the cells of the gland secreted a juice which is colorless and clear, known as the pancreatic juice. This juice is passed on to duodenum by mixing with the bales. It helps in the digestion of protein and being alkaline it neutralizes almost equal volume of gastric juice.
The liver is the biggest gland of the body. It is reddish in color and about 4 pounds or one kilogram in weight. It is situated on the right side of the body behind the lower ribs and below the diaphragm.
In healthy person it extends to about half an inch below the ribs and can be felt during inspiration. The liver is made up of numerous small cells which secrete bile from the blood carried in the blood-vessels which pas through it. There is a side bag attached to the liver, which is known as Gall bladder. The bile is stored in the gall bladder. Then it is passed on to duodenum through a duct. When there is no food in the stomach to be digested, then the bile remains in the gall bladder. Bile emulsifies fat, prevents food from decomposing and forming gas and helps the digested food to pass easily along the alimentary canal. It is afterwards partly absorbed by the intestine, gets in to blood, and helps to keep up the heart of the body.
A substance called glycogen is formed in the liver in large amount with becomes converted into sugar, and utilized by the body to give energy. The excess quantity of sugar passes out of the system in the urine and the disease i3 known as diabetes.