FUNCTIONS OF STOMACH

FUNCTIONS OF STOMACH

1. MECHANICAL FUNCTION

i. Storage Function

Food is stored in the stomach for a long period, i.e. for 3 to 4 hours and emptied into the intestine slowly.

The maximum capacity of stomach is up to 1.5 L. Slow emptying of stomach provides enough time for proper digestion and absorption of food substances in the smallintestine.

ii. Formation of Chyme

Peristaltic movements of stomach mix the bolus with gastric juice and convert it into the semisolid material known as chyme.

2. DIGESTIVE FUNCTION

Refer functions of gastric juice.

3. PROTECTIVE FUNCTION

Refer functions of gastric juice.

 4. HEMOPOIETIC FUNCTION

Refer functions of gastric juice.

5. EXCRETORY FUNCTION

Many substances like toxins, alkaloids and metals are excreted through gastric juice.

PROPERTIES AND COMPOSITION OF GASTRIC JUICE

Gastric juice is a mixture of secretions from different gastric glands.

PROPERTIES OF GASTRIC JUICE

Volume : 1200 mL/day to 1500 mL/day.

Reaction : Gastric juice is highly acidic with a pH of 0.9 to 1.2. Acidity of gastric juice is

due to the presence of hydrochloric acid.

Specific gravity : 1.002 to 1.004

COMPOSITION OF GASTRIC JUICE

Gastric juice contains 99.5% of water and 0.5% solids. Solids are organic and inorganic substances.

FUNCTIONS OF GASTRIC JUICE

1. DIGESTIVE FUNCTION

Gastric juice acts mainly on proteins. Proteolytic enzymes of the gastric juice are pepsin and rennin.

Gastric juice also contains some other enzymes like  gastric lipase, gelatinase, urase and gastric amylase.

Pepsin

Pepsin is secreted as inactive pepsinogen. Pepsinogen is converted into pepsin by hydrochloric acid. Optimum pH for activation of pepsinogen is below 6.

Action of pepsin

Pepsin converts proteins into proteoses, peptones and polypeptides. Pepsin also causes curdling and digestion of milk (casein).

Gastric Lipase

Gastric lipase is a weak lipolytic enzyme when compared to pancreatic lipase. It is active only when the pH is between 4 and 5 and becomes inactive at a pH below Gastric lipase is a tributyrase and it hydrolyzes tributyrin (butter fat) into fatty acids and glycerols.

Actions of Other Enzymes of Gastric Juice

i. Gelatinase: Degrades type I and type V gela tin and type IV and V collagen (which are proteoglycans

in meat) into peptides

ii. Urase: Acts on urea and produces ammonia

iii. Gastric amylase: Degrades starch (but its action is insignificant)

iv. Rennin: Curdles milk (present in animals only).

2. HEMOPOIETIC FUNCTION

Intrinsic factor of Castle, secreted by parietal cells of gastric glands plays an important role in erythropoiesis. It is necessary for the absorption of vitamin B12 (which is called extrinsic factor) from GI tract into the blood. Vitamin B12 is an important maturation factor during erythropoiesis. Absence of intrinsic factor in gastric juice causes deficiency of vitamin B12, leading to

pernicious anemia .

PROTECTIVE FUNCTION – FUNCTION OF MUCUS

Mucus is a mucoprotein, secreted by mucus neck cells of the gastric glands and surface mucus cells in fundus, body and other parts of stomach. It protects the gastric wall by the following ways:

Mucus:

i. Protects the stomach wall from irritation or mechanical injury, by virtue of its high viscosity.

ii. Prevents the digestive action of pepsin on the wall of the stomach, particularly gastric mucosa.

iii. Protects the gastric mucosa from hydrochloric acid of gastric juice because of its alkaline

nature and its acidcombining power.

4. FUNCTIONS OF HYDROCHLORIC ACID

Hydrochloric acid is present in the gastric juice:

i. Activates pepsinogen into pepsin

ii. Kills some of the bacteria entering the stomach along with food substances. This action is called

bacteriolytic action

iii. Provides acid medium, which is necessary for the action of hormones.

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