In a human being the ingestion of food is brought about in mouth where it is crushed into fine pieces by teeth.
The digestion in human beings takes place in a well developed system of organs called as digestive system. The digestive system of a man is a canal connected to a number of glands secreting different types of digestive juices. Thus, the system of alimentary canal and associated glands is called as digestive system.
The human digestive system comprises a number of parts like – mouth, stomach, duodenum, small intestine or ileum, and rectum or colon. The glands associated with the digestive system are – gall bladder, pancreas, and gastric glands. The gastric glands are found inside the wall of the stomach. It is this wall which also contains glands secreting Hydrochloric acid.
Digestion in Human Beings
Digestion in different parts of human digestive system is being detailed here.
Digestion in mouth:
The ingestion of food in a man starts from the buccal cavity or the mouth. Here, the solid food is converted into fine pieces by teeth. It is the time when saliva comes out from the salivary glands and gets mixed with the food. It has a carbohydrate digesting enzyme called as Ptyalin or the salivary amylase which converts carbohydrate to Maltose. Since maltose is a sweet substance, the bread tastes sweet when chewed for some time. Now, the food is pushed into the stomach.
All along the digestive canal the food is to be moved in a regulated manner in order to be processed properly. The lining of the whole digestive canal has muscles. These muscles contract and relax rhythmically and help in the forward movement of the food. This movement is called as Peristaltic movement.
Digestion in stomach:
From mouth the food reaches to the stomach through esophagus or the food pipe which extends from mouth to stomach. When food reaches into stomach, its wall starts secreting hydrochloric acid which has two basic functions- (1) It makes the medium acidic so as to activate the digestive enzymes, and (ii). It kills the germs of diseases if found with the food.
The wall of stomach has gastric glands that secrete gastric juice. The gastric juice has two basic protein digesting enzymes- (i) Pepsin, and (ii) Rennin or Chymosin. Pepsin digests insoluble protein into peptone. Rennin which is basically found in ruminants and in human infants converts the milk protein casein into Para casein. It is found before the formation of pepsin.
Digestion in Small Intestine
Besides the above, mucus is also secreted by the wall of the stomach. It protects the wall from the acid and facilitates easy movement of food. After the digestion of some part of protein in the stomach, the food is pushed ahead into small intestine through the SPHINCTER muscle. This muscle regulates the transfer of food in small amounts from stomach to small intestine. The part of small alimentary canal adjacent to stomach is a loop like tubular extension called as the duodenum. It is connected with two glands- the gall bladder and the Pancreas, with a branched tube. The Gall bladder is associated with liver. What is liver?
Liver is the largest glad in our body. It is the gland which functions as a centre of the synthesis of a large number of Plasma Proteins. Besides plasma proteins, it also synthesizes urea, bile salts and cholesterol. It is in this gland that the detoxification and destruction of hemoglobin which is released from the dead red blood cells takes place.
The gall bladder is a spherical body which stores bile juice, an alkaline fluid. It is secreted by liver cells and it has following functions-
(i). It makes the medium alkaline so as to activate enzymes contained in the pancreatic juice.
(ii). It kills the bacteria existing within the food.
(iii). It simplifies fat by breaking it into small pieces. This process is called as Emulsification.
A duct from the Pancreas joins the bile duct in the mid – way. The pancreatic juice from pancreas flows through the duct and joins the food. Its enzymes get activated on reaching to alkaline medium.
The pancreatic juice from pancreas flows through the duct and joins the food. Its enzymes get activated on reaching into alkaline medium. The pancreatic juice contains three main enzymes –Trypsin, Amylase, and Lipase. Trypsin acts on peptone and converts it into peptides and amino acids. Amylase converts maltose into glucose, and lipase digests the emulsified fat into fatty acids and glycerol.
The duodenum is followed by a short and straight portion of alimentary canal which is called as Jejunum. It is followed by a large and coiled part of the alimentary canal called as Ileum. It is the largest part of the alimentary canal which is about 6.5 meter long in an adult. In spite of being large, it is called as small because it is narrow. The length of the small intestine is less in a carnivore. Herbivores eat vegetables that contain cellulose. It is digested with difficulty. Hence, herbivores have large small intestine. Meat is easier to digest in the upper part of the food pipe itself. Hence, a tiger has small intestine.
The wall of the small intestine has glands that secrete intestinal juice. It contains a number of enzymes that complete the remaining part of digestion. Now the carbohydrate is finally digested into glucose, protein into amino acids, and fat into fatty acids and glycerol. Vitamins and minerals need simple breakdown from their compounds and don’t need digestion. Water still remains with the food.
Absorption of Digested Food
The inner wall of small intestine has a number of fingerlike projections called as villi. These villi provide small intestine a large surface area which helps in the fast absorption of digested food.
Each villus contains blood vessels and lymph vessels (called as lacteal). All the digested food is absorbed into blood except fatty acids and glycerol that are absorbed into lymph. The absorbed nutrients pass through blood stream and reach to all cells of the body.
When food is transferred into the large intestine, its water content is absorbed into blood to provide the undigested food a semisolid form. The muscles of the large intestine or rectum contracts to egest or release out the undigested food. This is called as Egestion or defecation.
nutrition, human beings, digestion, absorption