Multiple Choice
Which gastric secretion from the stomach lining contains both hydrochloric acid and pepsin?
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23. The Digestive System
The Stomach
Problem 27
Textbook Question
How does each of the three phases of gastric secretion promote and facilitate gastric control?
Verified step by step guidance1
Understand that gastric secretion is regulated in three phases: the cephalic phase, the gastric phase, and the intestinal phase. Each phase plays a distinct role in promoting and facilitating gastric control.
In the cephalic phase, sensory inputs such as sight, smell, taste, or thought of food stimulate the central nervous system. This triggers the vagus nerve to release acetylcholine, which stimulates gastric glands to secrete gastric juice (including hydrochloric acid and pepsinogen) in preparation for digestion.
In the gastric phase, the presence of food in the stomach stretches the stomach walls, activating stretch receptors. This triggers local reflexes and the release of gastrin, a hormone that further stimulates the secretion of gastric juice and enhances stomach motility.
In the intestinal phase, partially digested food (chyme) enters the small intestine. Initially, this stimulates the release of intestinal gastrin, which briefly promotes gastric secretion. However, as the intestine fills, inhibitory signals such as the release of secretin and cholecystokinin (CCK) slow gastric activity to allow the intestine to process the chyme effectively.
Recognize that these phases work in a coordinated manner to ensure efficient digestion and absorption of nutrients, while also preventing overloading of the digestive system.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Gastric Secretion Phases
Gastric secretion occurs in three phases: the cephalic phase, gastric phase, and intestinal phase. The cephalic phase is triggered by the sight, smell, or thought of food, stimulating the brain to signal the stomach to prepare for digestion. The gastric phase begins when food enters the stomach, leading to the release of gastric juices. Finally, the intestinal phase occurs as chyme enters the small intestine, regulating gastric activity to ensure proper digestion.
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Hormonal Regulation
Hormones play a crucial role in gastric secretion and control. Key hormones include gastrin, which stimulates the secretion of gastric acid, and secretin, which regulates the pH of the stomach contents. These hormones are released in response to food intake and help coordinate the digestive process, ensuring that the stomach operates efficiently and effectively during each phase of gastric secretion.
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Nervous System Involvement
The autonomic nervous system significantly influences gastric secretion. The parasympathetic nervous system, particularly through the vagus nerve, enhances gastric secretions during the cephalic phase. Conversely, the sympathetic nervous system can inhibit gastric activity during stress or danger. This balance between the two systems ensures that gastric control is finely tuned to the body's needs during digestion.
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