Digestion in The Stomach

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GASTRIC GLANDS

Tubular glands which extend from the bottom of the gastric foveola

to the muscularis mucosa. On the basis of their location, the gastric glands

are divided into cardiac glands which are short and tortuous and the fundic

glands which are straight slender glands with narrow lumen and made up

of Mucous cells, pepsinogen or chief cells and parietal or exyntic cells. The

pyloric glands in the pyloric region of the stomach are short and tortuous.

Stimulation of parasympathetic vagus gives rise to secretion of the gastric

juice rich in acid and enzymes. It also increases gastric secretion. The

secretion is mediated through release of acetylchlorine.

GASTRIC JUICE AND THE SECRETION

The gastric juice is the product of surface epithelium and the various

glands. The volume of the gastric juice secreted in man is 1200 – 1500ml

per day, pH become 2-3 when the gastric juice mixes with the food.

Specific gravity is 1.002 – 1.004.

The major constituents are water, HCl, enzymes – pepsin, rennin,

gastric lipase, gelatinase and mucus, electrolytes as sodium, potassium,

calcium, phosphate, bicarbonate and sulphate.

HCl SECRETIONS

Hydrochloric acid is secreted by oxyntic cells parietal cells or

secreting cells. These contain small channels called canaliculi which

communicate with the lumen of the gastric gland. The HCl is secreted by

the membrane of these canaliculi. It is an active process involving

expenditure of energy, O2 utilization, CO2 evolution and enzymes systems

participation. Secretion of 1gm molecular weight of HCl requires

expenditure of 10,000 gram calories of energy. The source for hydrogen

ions is water and the source for chloride ions is Nacl of blood. Hydrogen

ions are formed by dissociation of water into hydrogen and Hydroxyl ions.

This is the main source of hydrogen ions. The hydrogen ions combines

with OH ions H2O and HCO3 ions are released into the interstitial fluid and

blood.

In a simple way, the reactions involved are,

CO2 + H2 +NaCl

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