NUTRITION IN HUMAN BEINGS
- Parts of the body concerned with the uptake and digestion of food and elimination of indigestible remains form the digestive system, also called ‘alimentary system’.
- The human digestive system consists of an alimentary canal and many digestive glands.
- The alimentary canal is a long tube with muscular walls, glandular epithelial lining, and varying diameter.
- It opens out at the upper and lower ends, and most of it lies in the abdomen in a much-coiled form.
PARTS OF THE HUMAN DIGESTIVE SYSTEM
- Mouth or Buccal Cavity: The mouth has teeth and tongue
- The tongue has gustatory receptors which perceive the sense of taste.
- Tongue helps in turning over the food, so that saliva can be properly mixed in it.
- Salivary glands secrete saliva. Saliva makes the food slippery which makes it easy to swallow the food.
- Saliva also contains the enzyme salivary amylase or ptyalin. Salivary amylase digests starch and converts it into sucrose.
- Teeth help in breaking down the food into smaller particles so that swallowing of food becomes easier.
Types of Teeth
- There are four types of teeth in human beings.
- The incisor teeth are used for cutting the food.
- The canine teeth are used for tearing the food and for cracking hard substances.
- The premolars are used for coarse grinding of food.
- The molars are used for fine grinding of food.
Parts of The Human Digestive System
- Stomach is a wide, J-shaped bag-like organ. Highly muscular walls of the stomach help in churning the food.
- The stomach has 4 regions: cardiac part, fundus, body and pyloric part.
- The walls of the stomach secrete hydrochloric acid.
- It makes the medium inside the stomach acidic.
- The acidic medium is necessary for gastric enzymes to work.
- The enzyme pepsin secreted in the stomach; does partial digestion of protein.
- The mucus secreted by the walls of the stomach saves the inner lining of the stomach from getting damaged from hydrochloric acid.
Functions of Stomach
- The stomach serves 4 main functions: storage of food, mechanical churning of food, partial digestion, and regulation of the flow of food into the small intestine.
- It is a highly coiled tube-like structure.
- The small intestine is longer than the large intestine.
- It is the longest part of the alimentary canal.
- The small intestine is the site of the complete digestion of carbohydrates, proteins and fats. It receives the secretions of the liver and pancreas for this purpose.
- The small intestine is divided into three parts, viz. duodenum, jejunum and ileum.
- Liver is the largest organ in the human body.
- Liver manufactures bile: which gets stored in gallbladder.
- Pancreas is situated below the stomach.
- It secretes pancreatic juice which contains many digestive enzymes.
- Bile and pancreatic juice go to the duodenum through a hepato-pancreatic duct.
- Bile breaks down fat into smaller particles.
- This process is called emulsification of fat.
- After that, the enzyme lipase digests fat into fatty acids and glycerol.
- Trypsin and chymotrypsin are enzymes which digest protein into amino acids.
- Complex carbohydrates are digested into glucose.
- The major part of digestion takes place in the duodenum.
- No digestion takes place in jęjunum.
- The inner wall in the ileum is projected into numerous finger-like structures; called villi
- Digested food is absorbed by villi.
- Large intestine is smaller than small intestine.
- Undigested food goes into the large intestine.
- Some water and salt are absorbed by the walls of the large intestine.
- After that, the undigested food goes to the rectum: from where it is expelled out through the anus.