MOVEMENTS OF STOMACH

MOVEMENTS OF STOMACH

Activities of smooth muscles of stomach increase during gastric digestion (when stomach is filled with food) and when the stomach is empty.

Types of movements in stomach

1. Hunger contractions

2. Receptive relaxation

3. Peristalsis.

1. HUNGER CONTRACTIONS

Hunger contractions are the movements of empty stomach. These contractions are related to the sensations of hunger. Hunger contractions are the peristaltic waves superimposed over the contractions of gastric smooth muscle as a whole. This type of peristaltic waves is different from the digestive peristaltic contractions. The digestive peristaltic contractions usually occur in body and pyloric parts of the stomach. But, peristaltic contractions of empty stomach involve the entire stomach. Hunger contractions are of three types:

Type I Hunger Contractions

Type I hunger contractions are the first contractions to appear in the empty stomach, when the tone of the

gastric muscles is low. Each contraction lasts for about 20 seconds. The interval between contractions is about 3 to 4 seconds. Tone of the muscles does not increase between contractions. Pressure produced by these contractions is about 5 cm of H2O.

Type II Hunger Contractions

Type II hunger contractions appear when the tone of stomach is stronger. Tone increases in stomach if food intake is postponed, even after the appearance of the type I contractions. Each of the type II contractions lasts for 20 seconds like type I contractions. But the pause between the contractions is decreased. Pressure produced by these contractions is 10 to 15 cm of H2O.

Type III Hunger Contractions

Type III hunger contractions are like incomplete tetanus. These contractions appear when the hunger becomes severe and the tone increases to a great extent. Type III hunger contractions are rare in man as the food is taken usually before the appearance of these contractions. These contractions last for 1 to 5 minutes. The pressure produced by these contractions increases to 10 to 20 cm of H2O. When the stomach is empty, the type I contractions occur first, followed by type II contractions. If food intake

is still postponed, then type III contractions appear and as soon as food is consumed, hunger contractions

disappear.

2. RECEPTIVE RELAXATION

Receptive relaxation is the relaxation of the upper portion of the stomach when bolus enters the stomach from esophagus. It involves the fundus and upper part of the body of stomach. Its significance is to accommodate the food easily, without much increase in pressure inside the stomach. This process is called accommodation of stomach.

3. PERISTALSIS

When food enters the stomach, the peristaltic contraction or peristaltic wave appears with a frequency of 3 per minute. It starts from the lower part of the body of stomach, passes through the pylorus till the pyloric sphincter.

Initially, the contraction appears as a slight indentation on the greater and lesser curvatures and travels

towards pylorus. The contraction becomes deeper while traveling. Finally, it ends with the constriction of pyloric sphincter. Some of the waves disappear before reaching the sphincter. Each peristaltic wave takes about one minute to travel from the point of origin to the point of ending. This type of peristaltic contraction is called digestive peristalsis because it is responsible for the grinding of food particles and mixing them with gastric juice for digestive activities.

FILLING AND EMPTYING OF STOMACH

FILLING OF STOMACH

While taking food, it arranges itself in the stomach in different layers. The first eaten food is placed against the greater curvature in the fundus and body of the stomach. The successive layers of food particles lie nearer, the lesser curvature, until the last portion of food eaten lies near the upper end of lesser curvature, adjacent to cardiac sphincter. The liquid remains near the lesser curvature and flows towards the pyloric end of the stomach along a V-shaped groove. This groove is formed by the smooth

muscle and it is called magenstrasse. But, if a large quantity of fluid is taken, it flows around the entire food mass and is distributed over the interior part of stomach, between wall of the stomach and food mass.

EMPTYING OF STOMACH

Gastric emptying is the process by which the chime from stomach is emptied into intestine. Food that is

swallowed enters the stomach and remains there for about 3 hours. During this period, digestion takes place. Partly digested food in stomach becomes the chyme.