Digestion in small intestine. in biology

Digestion in small intestine. In biology:- partially digestion food is finally digested and absorbed in the intestine. Perisataltic movements start throughout the small intestine as soon as food reaches in it. Due to these movement, chyme is propelled forward in small intestine. Enzymes also throughly mix due to these movements.

Three types of digestive juices are secreted in small intestine:-

pancreatic juice from the pancreas, bile juice from liver and intestinal juice.

When the food enters into duodenum and intestine, the endocrine cells present in the mucosa of duodenum and intestine secrete hormones in blood in response to acidic pH, derived proteins and fat present in food. These hormones stimulate and regulate the actions of liver, gall bladder, pancreas and intestine. The hormones secreted by duodenum are:

  1. Pancreozymin:- It stimulates the pancreas to secrete a thick fluid having more enzymes and less bicarbonate ions.
  2. Secretin:- It stimulates the pancreas to secrete a watery fluid having more of bicarbonate ions and less enzymes.
  3. Hepatocrinin:- Hepatocrinin stimulates liver to produce dilute bile.

pancreatic juice:-

Pancreatic juice is a thin, colourless and alkaline fluid having a pH value 8. On an average 600-800 ml of pancretic juice is secreted daily. Being alkaline it neutralizes the acidity of chyme. It has about 98 percent water and 2 percent enzymes and salt. Enzymes of pancreatic juice and their functions are as follows.

  • Trypsinongen
  • Chymotrypsinogen
  • Carboxypeptidase
  • Amylopsin
  • Steapsin
  • Cholesterolesterase

Bile :-

bile is secreted by hepatic cells. About 500-1000 ml of bile is secreted daily in human being. some amount of bile is stored in gall bladder. The bile secreted from liver is a yellow transparent fluid while the bile stored in the gall bladder is dense and nearly blackish.

The composition and colour of bile of gall bladder changes due to the mixing to mucin and absorption of salts and water from it.

Bile is bitter in taste and has a specific smell. The pH of hepatic bile is 7.1 to 7.3 while that of gall bladder is 6.9-7.7.

Bile contains 92 percent water. following other substance are found in bile.

  • Bile acids
  • Bile salts
  • bile pigments

Intestinal juice or succus entericus:-

About 2-3 litres of intestinal juice is secreted from intestine daily. its secretion is controlled by a hormone called enterocrinin secreted by duodenum and jejunum. Intestinal juice is light pale alkaline fluid having pH value 7-8. it has 98-98.5% organic and 1.5 % inorganic substance. organic substance include enzymes while inorganic substance mainly include sodium bicarbonate and sodium chloride.

Enzymes of the intestinal juice and their funcation are enlisted below.

  • Erepsin
  • Disachharidases
  • Nucleases
  • Nucleotidases
  • Nucleosidases
  • Phosphatases
  • lipase
  • Enterokinase