Where does the absorption of most nutrients take place?

Correct Answer: B

Rationale: The correct answer is B: small intestine. The absorption of most nutrients occurs in the small intestine due to its large surface area, which is facilitated by villi and microvilli. Digestive enzymes and bile produced by the liver and pancreas help break down food into absorbable nutrients. Nutrients like carbohydrates, proteins, fats, vitamins, and minerals are absorbed through the walls of the small intestine and into the bloodstream for distribution to the body. The stomach primarily functions in digestion, while the large intestine absorbs water and salts and the rectum stores waste before elimination.

Correct Answer: A

Rationale: The correct answer is A: Parietal cells. Parietal cells secrete hydrochloric acid in the stomach to create the acidic environment necessary for digestion. They also secrete intrinsic factor for vitamin B12 absorption. Chief cells produce pepsinogen, not hydrochloric acid. Mucous neck cells secrete mucus to protect the stomach lining. Enteroendocrine cells secrete hormones like gastrin, not hydrochloric acid. Therefore, the correct choice is A as it directly produces hydrochloric acid in the stomach.

Correct Answer: C

Rationale: The correct answer is C because the defecation reflex is integrated in a control center in the sacral spinal cord. This is due to the presence of the parasympathetic nerves that control the smooth muscles of the colon and rectum in the sacral region. The sacral spinal cord is responsible for coordinating the reflexive relaxation of the internal anal sphincter and contraction of the rectum during defecation. Choices A and B are incorrect because the initiation and integration of the defecation reflex do not involve the anal canal stretching or the lumbar spinal cord. Choice D is incorrect as the defecation reflex is not controlled by the vagus nerve, which is primarily responsible for the parasympathetic innervation of organs in the thorax and upper abdomen.

Correct Answer: C

Rationale: The correct answer is C: Lactase. Lactase is an enzyme produced in the small intestine, not in the pancreas. The exocrine pancreas secretes digestive enzymes like chymotrypsinogen, proelastase, and lipase to aid in the digestion of proteins, fats, and carbohydrates. Lactase is responsible for breaking down lactose, a sugar found in dairy products, and is produced in the small intestine. Therefore, C is the correct answer. Choices A, B, and D are incorrect because chymotrypsinogen, proelastase, and alph are all enzymes produced by the pancreas to aid in digestion.

Correct Answer: D

Rationale: The correct answer is D because G cells in the gastric pit secrete gastrin, not histamine. Gastrin stimulates the release of hydrochloric acid in the stomach. Mucous cells are not enteroendocrine, so A is incorrect. G cells are not exocrine, making B incorrect. D cells secrete somatostatin, not histamine, so C is also incorrect.