During the cephalic phase of gastric secretion?
the stomach responds to distention production of gastric juice slows down. secretin inhibits parietal and chief cells
the intestinal reflex inhibits gastric emptying
there is an increased flow of action potentials along the vagus nerve to the stomach .
there is an increased flow of action potentials along the vagus nerve to the stomach. The cephalic phase is the preparatory phase of gastric secretion that begins before food enters the stomach. It is triggered by the sight, smell, taste, or anticipation of food. In this phase, the brain sends signals through the vagus nerve to stimulate the secretion of gastrin, a hormone that triggers the release of gastric juice. The increased flow of action potentials along the vagus nerve results in the release of acetylcholine, which stimulates parietal and chief cells to produce gastric juice.
During the cephalic phase of gastric secretion, several events occur:
1. Stomach Responds to Distention: When food enters the mouth and stimulates taste buds, it triggers the cephalic phase. As the food is chewed and swallowed, the stomach responds to the distention caused by the incoming food. This distention activates the mechanoreceptors in the stomach, initiating gastric reflexes.
2. Production of Gastric Juice Slows Down: Despite the initial distention, the production of gastric juice actually slows down during the cephalic phase. This is because the stomach receives signals from the brain (via the vagus nerve) that suppress the release of gastric juice. The purpose of this slowdown is to prevent excessive acid secretion before the food reaches the stomach.
3. Secretin Inhibits Parietal and Chief Cells: Secretin is a hormone produced by the duodenum (a part of the small intestine). During the cephalic phase, secretin is released in response to the presence of certain substances in the mouth, stomach, or small intestine. Secretin inhibits the activity of parietal and chief cells in the stomach, which leads to a decrease in the production of gastric acid.
4. Intestinal Reflex Inhibits Gastric Emptying: Another effect of the cephalic phase is the inhibition of gastric emptying. As food enters the stomach, the intestine sends signals back to the stomach via the enterogastric reflex. This reflex slows down the rate of gastric emptying to allow for better digestion and absorption of nutrients in the small intestine.
5. Increased Flow of Action Potentials Along the Vagus Nerve to the Stomach: The vagus nerve, also known as cranial nerve X, plays a crucial role in the regulation of digestion. During the cephalic phase, there is an increased flow of action potentials along the vagus nerve to the stomach. These signals stimulate the release of gastric juice, increase stomach motility, and promote gastric activity in preparation for the arrival of food.
Overall, the cephalic phase of gastric secretion involves a coordinated response of the stomach to the presence of food, which includes slowing down gastric acid production, inhibiting gastric emptying, and increasing vagal stimulation to enhance digestion.