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.
