DIGESTION AND ABSORPTION

 

In the intestine :

  • Important secretion added to the intestine during digestion:
    • Bile juice.
    • Pancreatic juice.
    • Intestinal juice or succus entericus.

  • The pancreatic juice contain following enzymes:
    • Trypsinogen
    • Chymotrypsinogen
    • Procarboxypeptidase.
    • Amylases
    • Lipases
    • Nucleases.

  • Trypsinogen is activated by an enzyme, enterokinase secreted by intestinal mucosa into active trypsin.
  • Active trypsin activates other enzymes in the pancreatic juice in the intestine.
  • The bile released into the duodenum contains –
    • Bile pigments (bilirubin and bili-verdin)
    • Bile salts. (Bicarbonate, tourocholate, glycolate)
    • Cholesterol and
    • Phospholipids.

  • Bile salt helps in emulsification of fat, i.e. breakdown fats into small micelles.
  • Bile also activates lipases.
  • The intestinal mucosa contains goblet cells which secrete mucus.
  • The secretion of brush border cells of intestinal mucosa and the goblet cells constitute the intestinal juice or succus entericus.
  • The intestinal juice contains variety of enzymes –
    • Disaccharidases (maltase, lactase and invertase)
    • Dipeptidases.
    • Lipases.
    • Nucleosidases.

  • Sub-mucosal glands (Brunner’s glands) also secrete alkaline fluid to counter act acidic chyme before secretion of bile and pancreatic juice.

ABSORPTION OF DIGESTED PRODUCTS :

  • Absorption is the process by which the end product of digestion passes through the intestinal mucosa into the blood or lymph.
  • Absorption is carried out by passive, active or facilitated transport mechanism.
  • Glucose, amino acids and electrolytes are absorbed by simple diffusion into the blood in the concentration gradient.
  • Fructose and some amino acids absorbed with the help of carrier ions like Na+. This is called facilitated diffusion.
  • Active transport of digested food and electrolytes takes place against the concentration gradients hence require energy.

Absorption of fatty acid and glycerol.

  • Fatty acids and glycerol being insoluble cannot be absorbed into blood.
  • They are transported into mucosal epithelium and triglycerides are formed.
  • Triglycerides are covered by a protein coat to form small fat globules called chylomicron, which are incorporated into the lacteal in the villi.
  • These lymphatic vessels ultimately release the absorbed substances into the blood stream later on.

Assimilation and egestion :

  • The absorbed substances finally reach the tissues which utilize them for their activities. This process is called assimilation.
  • The digestive wastes, solidified into coherent faeces in the rectum and removed to outside periodically by the process called defaecation.

DISORDERS OF DIGESTIVE SYSTEM :

Jaundice :

  • Affected organ is the liver.
  • Skin and eyes turn yellow due to deposition of bile pigments.

Vomiting :

  • Ejection of stomach contents through the mouth.
  • It is controlled by the vomit centre in the medulla oblongata.
  • A feeling of nausea precedes vomiting.

Diarrahoea :

  • Abnormal frequency of bowel movement and increased liquidity of the faecal discharge.
  • It reduces the absorption of food.

Constipation :

  • The faeces are retained in the rectum as the bowel movements occurs irregularly.

Indigestion :

  • The food is not properly digested leading to a feeling of fullness.
Causes are inadequate enzymes secretion, anxiety, food poisoning, over eating and spicy food.

 

CBSE Biology (Chapter Wise) Class XI ( By Mr. Hare Krushna Giri ) 
Email Id : [email protected]