A drop in pH below 4.5 in the duodenum stimulates the secretion of
(a) Secretin
(b) Cholecystokinin
(c) Gastrin
(d) All of these

검증된 단계별 안내

Understand the physiological context: The duodenum is the first part of the small intestine where acidic chyme from the stomach enters, and its pH can influence hormone secretion.

Recall that secretin is a hormone released by the S cells of the duodenum in response to acidic pH (typically below 4.5) to help neutralize the acid by stimulating bicarbonate secretion from the pancreas.

Recognize that cholecystokinin (CCK) is primarily released in response to fats and proteins in the duodenum, not directly by low pH.

Know that gastrin is secreted by the stomach in response to food and stimulates acid secretion, but it is not primarily triggered by low pH in the duodenum.

Conclude that a drop in pH below 4.5 in the duodenum specifically stimulates the secretion of secretin to protect the intestinal lining and regulate pH.

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주요 개념

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pH and its Role in the Digestive System

pH measures the acidity or alkalinity of a solution. In the digestive system, different sections have specific pH ranges that regulate enzyme activity and hormone secretion. A drop in pH below 4.5 in the duodenum indicates increased acidity, triggering hormonal responses to protect the intestine and aid digestion.

Secretin and its Function

Secretin is a hormone released by the S cells of the duodenum in response to acidic chyme entering from the stomach. It stimulates the pancreas to secrete bicarbonate-rich fluid, which neutralizes the acid, protecting the intestinal lining and creating an optimal pH for digestive enzymes.

Cholecystokinin and Gastrin

Cholecystokinin (CCK) is released in response to fats and proteins, stimulating bile and pancreatic enzyme secretion. Gastrin primarily stimulates gastric acid secretion in the stomach. Unlike secretin, neither CCK nor gastrin is directly triggered by low pH in the duodenum.

A drop in pH below 4.5 in the duodenum stimulates the secretion of(a) Secretin(b) Cholecystokinin(c) Gastrin(d) All of these