Digestion Q1 Flashcards
What are the hormones of digestion? Where are they made? When are they released? What do they signal or do, and how are they inhibited? Discuss these in terms of digestion.
The gastric phase is activated by swallowing food (which stretches the stomach and raises the pH of its contents).
Gastric secretion is stimulated by 3 chemicals: 1. Acetylcholine, 2. Histamine, and 3. Gastrin
All 3 chemicals stimulate parietal cells to secrete HCl and intrinsic factor. Chief cells secrete pepsinogen in response to gastrin and especially acetylcholine. This is a positive feedback loop that accelerates protein digestion. This is then inhibited once the stomach acid pH falls below a pH of 2 (becomes a negative feedback loop).
Secretin in the duodenum signals the secretion of sodium bicarbonate in the pancreas and that stimulates the secretion of bile in the liver. This hormone responds to the acidity of chyme.
Cholecystokinin (CKK) is also in the duodenum and stimulates the release of digestive enzymes in the pancreas and stimulates the emptying of bile in the gallbladder. This hormone is secreted in response to fat in chyme.
Gastric inhibitory peptide (GIP) is in the duodenum and decreases stomach churning in order to slow the emptying of the stomach. Another function is to induce insulin secretion.
Motilin (duodenum) increases the migrating myoelectric complex component of gastrointestinal motility and stimulates production of pepsin.
Discuss the Cephalic Phase of digestion.
The cephalic phase occurs before food enters the stomach, especially while its being eaten. This results from sight, smell, taste and the thought of eating food. The greater the appetite, the more intense the stimulation.
Neurogenic signals initiate the cephalic phase of gastric secretion from the cerebral cortex and in the appetite centers of the amygdala and the hypothalamus. These signals are transmitted through the dorsal motor nuclei of vagi, and then through the vagus nerve to the stomach.
