Which of the following is not a phase of gastric secretion?
A) cephalic
B) gastric
C) intestinal
D) enterogastric
The correct answer and explanation is :
The correct answer is D) enterogastric.
Explanation:
Gastric secretion is a complex process that involves several phases to regulate the production of digestive juices, such as gastric acid and enzymes, to aid in food digestion. There are three main phases of gastric secretion: the cephalic phase, the gastric phase, and the intestinal phase. However, the term enterogastric does not refer to one of the phases of gastric secretion, but rather describes a regulatory mechanism.
- Cephalic Phase:
- This phase is initiated by sensory stimuli, such as the sight, smell, taste, or even the thought of food. The brain sends signals to the stomach to prepare for digestion by stimulating the vagus nerve. This increases the secretion of gastric juices, including hydrochloric acid (HCl) and pepsinogen, even before food enters the stomach. This phase accounts for about 30% of the total gastric secretion.
- Gastric Phase:
- The gastric phase is triggered when food enters the stomach. Stretch receptors in the stomach wall and the presence of proteins and peptides in the stomach trigger the release of gastric juices. This phase is responsible for the majority (about 60%) of gastric secretion. The hormone gastrin plays a key role in stimulating gastric acid production during this phase. Gastric motility also increases to help churn the food and mix it with digestive enzymes.
- Intestinal Phase:
- The intestinal phase begins once partially digested food (chyme) enters the small intestine. Initially, the presence of chyme in the duodenum stimulates gastric secretion. However, the release of certain hormones like secretin and cholecystokinin in response to acidic chyme also inhibits gastric secretion to prevent excessive acid production in the stomach. This phase primarily focuses on regulating the flow of chyme into the small intestine and ensuring proper digestion.
- Enterogastric Reflex (not a phase of gastric secretion):
- The term “enterogastric” refers to a reflex, not a phase. The enterogastric reflex helps regulate gastric secretion by signaling the stomach to reduce acid production when the small intestine becomes too full or when the pH in the duodenum drops too low. This is a feedback mechanism that slows down gastric motility and secretion to protect the stomach and ensure proper digestion.
In summary, while cephalic, gastric, and intestinal phases are recognized phases of gastric secretion, enterogastric is a term describing a reflex that regulates gastric activity, not a phase of secretion itself.