Regulation of gastric secretion

 

Regulation of Secretion of Gastric Juice

There are.always small quantity of gastric juice present in stomach. When it contains no food, known as fasting juice.

Both nervous and hormonal mechanism control gastric secretion.

Regulation of secretion of Gastric juice divided in three phase-

1. Cephalic ( Head phase)

2. Gastric phase ( Belly phase)

3. Intestinal phase

1. Cephalic Phase

Cephalic phase of digestion in which stomach responds to food sight, smell, taste, thought,   chewed or swallowed.

Stomach stimulates by activity of vegus nerve and gastric juice secreted.

Thoughts of food stimulate centres within medulla oblongata.

Cerebral cortex and feeding center in hypothalamus 

Send impulses

Medulla oblongata

Transmit impulses

To parasympathetic postaganglionic fibres in submucosal plexuses.

Parasympathetic fibres supply nerve to (supply nerve to smooth muscle of stomach to promote gastric motility)

Parietal cell, Chief cell, Mucus cell

Increase gastric secretion from all gastric glands.

2. Gastric phase

In gastric phase greatest volume of gastric secretion. Once food sources reaches in stomach.

Sensory receptors in stomach initiate. Both nervous and hormonal mechanism to ensure gastric secretion and motility.

Ingested food stimulates gastric activity in these ways-

a. By stretching the stomach

b. By raising pH of its content

c. Semi digested proteins and peptides

d. Stimulants; Alcohol, Coffein

Histamines stimulates parietal cell to produce HCL.

Mucous of (G- cell) in the pyloric antrum to secrete hormone Gastrin.

Food stretch the stomach and activates myenteric and vagovagal reflexes.

Stimulate gastric secretion

Histamines and gastrin stimulate acid and enzyme secretion.

Gastrin Function

1. Stimulate growth of glands

2. Secretion of large amount of gastric juice

3. Act as disinfectant and killing microbes

4. Increase motility of stomach

5. Cause contraction of lower esophageal sphincter

6. Stimulate parietal cell to produce HCL and Pepsinogen

3. Intestinal phase 

Entry of acidic stomach contents (chym) into the duodenum of small intestine.

Presence of chyme in duodenum initiates both neural and hormonal mechanism, which either stimulate or inhibit gastric secretion.

Excitatory component, presence of protein in duodenum release intestinal gastrin, stimulate gastric secretion.

Inhibitory component is activated by acidic chyme in duodenum, causes production of hormone, Which is carried by blood to the stomach.

Inhibitory components are -

Cholecystokinin (CCK)

Secretin

Gastric inhibitory peptide (GIP)

Where they turn off chief and parietal cells.