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:

• 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.

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:

• Liver is the largest organ in the human body.
• Liver manufactures bile: which gets stored in gallbladder.

Pancreas:

• 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.

Small Intestine

• 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:

• 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.