Parietal cells secrete .

Correct Answer: B

Rationale: The correct answer is B: hydrochloric acid. Parietal cells in the stomach secrete hydrochloric acid, which plays a crucial role in breaking down food and creating an acidic environment for digestion. Gastrin (choice A) is a hormone that stimulates acid secretion. Pepsin (choice C) is an enzyme produced by chief cells, not parietal cells. Pepsinogen (choice D) is the inactive precursor of pepsin. Therefore, the correct choice is hydrochloric acid as it directly relates to the function of parietal cells in the stomach.

Correct Answer: C

Rationale: The correct answer is C: cholecystokinin. Cholecystokinin is a hormone released by the small intestine in response to the presence of fatty acids and amino acids in the duodenum. It stimulates the gallbladder to contract and release bile into the small intestine to aid in the digestion and absorption of fats. Gastrin (A) stimulates acid secretion in the stomach. Secretin (B) stimulates the pancreas to release bicarbonate to neutralize stomach acid. Insulin (D) is a hormone that regulates blood sugar levels and does not play a role in bile release.

Correct Answer: A

Rationale: The correct answer is A: secretin. Secretin is a hormone produced by the small intestine in response to acidic chyme entering the duodenum. It stimulates the release of pancreatic juice from the pancreas, which helps neutralize the acidic chyme. Summary: B: Gastrin stimulates gastric acid secretion in the stomach. C: Cholecystokinin stimulates the release of bile from the gallbladder and pancreatic enzymes. D: Insulin regulates blood sugar levels by facilitating the uptake of glucose into cells.

Correct Answer: C

Rationale: The correct answer is C: pepsin. Pepsin is an enzyme produced in the stomach that specifically breaks down proteins into peptides. Amylase (A) digests carbohydrates, lipase (B) digests fats, and sucrase (D) digests sucrose. Pepsin is the only enzyme among the choices that is responsible for digesting proteins, making it the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Small intestine. The small intestine is where most of the absorption of nutrients occurs due to its large surface area and presence of villi and microvilli. These structures increase the absorption capacity, allowing for efficient absorption of nutrients like carbohydrates, proteins, fats, vitamins, and minerals. The stomach primarily functions in the digestion of food through the action of stomach acid and enzymes, while the large intestine mainly absorbs water and electrolytes. The mouth is responsible for initial digestion through chewing and production of saliva but does not play a significant role in nutrient absorption.