Question

How does food in the duodenum inhibit motility and secretions in the stomach? IM LOOKING FOR SOMEWHAT AN DETAIL OR NEAR TO DETAIL NEAR ,...A GOOD EXPLANATION FOR THIS QUESTION , i need to understand , thank u

Answer 1

Duodenal inhibition

They primarily stimulate the pancreas and gall bladder, but also suppress gastric secretion and motility. The effect of this is that gastrin secretion declines and the pyloric sphincter contracts tightly to limit the admission of more chyme into the duodenum.

The intestinal phase

The intestinal phase of gastric function is largely inhibitory. Gastric secretion and motility are both inhibited. In the duodenal phase, the food is mixed with the digestive secretions of the pancreas and liver. The inhibition of gastric emptying by food in the duodenum enables the duodenal contents to be processed before more material enters it from the stomach.

Secretion

Although food in the duodenum is largely inhibitory as far as gastric secretion is concerned, there is an early stimulatory phase in response to slight distension of the duodenum, probably due to the release of gastrin from APUD cells in the walls of the duodenum. However, appropriate stimulation of the duodenum inhibits gastric secretion. Inhibitory stimuli include distension of the duodenum, fats and peptides in the chyme, increased acidity, and hypertonic solutions. All of these stimuli cause the release of hormones from APUD cells. This phase of control of secretion is summarized.

Acid in the duodenal chyme causes the release of secretin, and fat in the duodenal chyme causes the release of CCK and GIP into the blood, and these hormones all inhibit secretion of gastric juice (see above). This is a feedback mechanism that prevents the duodenal contents becoming excessively acid. It is important for several reasons:

•

Digestive enzymes, which act in the small intestine require neutral or acid pH values for optimum activity

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Micelle formation, which is necessary for fat digestion and absorption in the small intestine will only take place at a neutral or slightly alkaline pH

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The duodenum is the most common site for ulcer formation in the digestive tract and acid is the prime cause of ulceration in this region. The reduction of acid secretion begins when the pH of the duodenal contents falls to 5.0, and it is complete at a pH value of approximately 2.5.

Control of the pH of the gastrointestinal tract helps to maintain the pH of the blood within normal limits . The effects of hypersecretion of acid on acid–base balance are described in Cases 4.1 and 4.2:

Motility

Motility in the stomach can be influenced by food in the duodenum, food in the ileum and food in the colon. Distension of the duodenum inhibits gastric motility via two mechanisms:

1.

A quick enterogastric reflex which employs nerve fibres in the vagus nerve and an unknown neurotransmitter.

2.

A slower humoral mechanism involving the release of hormones from the walls of the duodenum into the blood. These hormones are collectively known as enterogastrones. They include CCK and secretin.

When food material reaches the ileum, the emptying of the stomach is delayed. This is a neural reflex initiated by activation of mechanoreceptors in the walls of the ileum, which trigger action potentials in nerve fibres in the internal nerve plexi. Interestingly, when food enters the stomach the motility of the ileum is increased. Thus the ileogastric reflex operates in both directions.

There is also a neural reflex response when the chyme enters the colon; distension of the colon activates pressure receptors which triggers impulses in internal nerves to delay gastric emptying.