Small intestine, physiology.

 Physiology of small intestine 

Small intestine

What is small intestine,

Where is small intestine located.

Small intestine is the part of the alimetitary canal from the pyloric sphincter to the ileocecal sphincter It is divided into duodenum, jejunum and ileum and It extensively adapted for digestion and absorption due to presence of microvilli, villi and circular folds of its wall which provide a large surface area.

It is continuous with the stomach at pyloric sphincter and leads into large intestine at the ileocecal valve. The length of the small intestine is a little over 5 meters.

The villi are tiny finger-like projections of the mucosa layer of the intestinal lumen (about 0.5-1mm long). Their walls consist of columnar epithelial cells or enterocytes.

Because of their presence, the total surface of the small intestinal mucosa is tremendously increased. Numerous microvilli are seen on the surface of each enterocyte and these microvilli, in turn, increase the surface area of each enterocyte.

Fig. Intestinal gland and villi

The functions of small intestine

a. Onward movement of its contents by peristaltic and segmental movements.

b. The movement of small intestine helps to mix the chyme with panercatic juice, bile and succus entericos.

c. Secretion of intestinal juice.

d. Completion of chemical digestion of carbohydrate, protein and fat.

e. Protection against microbes that have survived the antimicrobial action of HCI in the stomach by the solitary lymph follicles and aggregated lymph follicles (Peyer's patches).

F .Secretion of local hormones like PZ-CCK, secretin motilin etc. These hormones control various gastrointertiral functions.

g. Absorption of nutrient materials.

INTESTINAL JUICE OR SUCCUS ENTERICUS

It is a digestive secretion of small intestine.

Properties:

Daily secretion. 2-3 Liters

PH. 7.5-8

Specific gravity. 1.002 1.020

Appearance. Colourless, odourless, watery fluid.

Functions: 

1. Digestive function

The intestinal juice contain enzymes meant for completing the digestion of food.

Protein digestion:

The proteolytic enzymes like dipeptidase, tripeptidase, amino-peptidase, carboxy peptidase etc. act upon dipeptide, tripeptide etc and converts them to amino acids.

Carbohydrate digestion

Disaccharides are acted upon by the disaccharidases and give rise to monosaccharides.

    

Lipid digestion

Intestinal lipase breaks triglycerides into monoglycerides, free fatty acids, and glycerol. Cholesterol esterase convert cholesterol esters into free cholesterol.

2. It takes part in the regulation of electrolyte balance.

3. It takes part in water balance.

4. Enterokinase is an activator. It converts trypsinogen to trypsin.

5. Mucin a. Itacts as a lubricating agent for food.

b. It protects the wall of the intestine from actions of enzymes.

6. Bicarbonate ions help in neutralizing the acidic food entering the small intestine.

Regulation of secretion: Secretion of intestinal juice is controlled by autonomic nervous system, by local nervous reflexes and by hormones. Increase in parasympathetic activities will increase the secretion of intestinal juice. Sympathetic stimulation will decrease the secretion of intestinal juice. When the food is inside the intestine it will generate a local reflex mechanism which will increase the production of intestinal juice.

Hormones: Enterocrinin

The presence of food inside the small intestine gives a physical as well as chemical stimulus. Because of this the wall of intestine secrete a local hormone enterocrinin. This hormone stimulates the gl

ands of the intestine and increases the production of intestinal juice.