Final answer:
Gastrin is a hormone that stimulates the secretion of gastric acid and activates smooth muscle contractions in the stomach.
Step-by-step explanation:
Gastrin is a hormone secreted by G cells in the stomach in response to the presence of proteins. It stimulates the secretion of gastric acid, or hydrochloric acid (HCl), by the parietal cells of the stomach mucosa. The release of gastrin from enteroendocrine G cells increases the production of HCl, which creates an acidic environment necessary for the conversion of pepsinogen to pepsin and protein digestion. Gastrin also activates smooth muscle contractions in the stomach. Therefore, the correct answer is (a) Gastrin increases the secretion by the gastric glands.
The hormone gastrin is secreted by G cells in the stomach and plays a critical role during the gastric phase of digestion. When a student asks, "Gastrin, which stomach cells secrete…," they are referring to the function of gastrin in the digestive process. The correct answer is that gastrin mainly increases the secretion by the gastric glands. Specifically, gastrin acts to stimulate parietal cells to increase their production of hydrochloric acid (HCl), which is essential for the digestion of proteins. Moreover, gastrin also activates smooth muscle contractions in the stomach. The gastric phase begins when food actually reaches the stomach, stretching it and activating receptors that trigger the secretion of gastric juice.