The stomach is unique to the GI tract because it contains

Correct Answer: D

Rationale: The correct answer is D: oblique smooth muscle. The stomach is unique in the GI tract because it contains an additional layer of muscle fibers called the oblique muscle layer. This layer allows for more efficient mixing and churning of food, aiding in digestion. Circular smooth muscle (choice A) and longitudinal smooth muscle (choice B) are present in various parts of the GI tract but are not unique to the stomach. Skeletal muscle (choice C) is not found in the stomach as the muscles responsible for its movement are smooth muscle.

Correct Answer: D

Rationale: The correct answer is D: enterokinase; small intestine. Enterokinase is an enzyme that activates trypsinogen into trypsin in the small intestine. Trypsin is then responsible for breaking down proteins in the small intestine. Enterokinase is not found in the pancreatic ducts, eliminating choices A and C. Trypsinogen is not activated by itself, so choice B is incorrect. In summary, enterokinase activates trypsinogen into trypsin in the small intestine, allowing for protein digestion.

Correct Answer: B

Rationale: The correct answer is B: lacteals. Chylomicrons are too large to enter capillaries directly, so they are absorbed into lacteals, specialized lymphatic vessels in the small intestine. Lacteals transport chylomicrons to the lymphatic system, eventually reaching the bloodstream via the thoracic duct. Arterioles and venules are part of the blood circulation system and are not directly involved in chylomicron absorption.

Correct Answer: D

Rationale: The correct answer is D because butyric acid, a short-chain fatty acid formed during colonic fiber fermentation, has been shown to stimulate antioxidant defenses in the colon. This helps protect against oxidative damage, a key factor in the development of cancer. Choice A is incorrect because propionic acid does not inhibit liver fatty acid synthesis in relation to colon cancer. Choice B is incorrect because butyric acid does not silence the SLC5A8 tumor suppressor gene; in fact, it has been shown to have anti-tumor effects. Choice C is incorrect as there is evidence supporting the protective effect of dietary fiber through butyric acid's stimulation of antioxidant defenses.

Correct Answer: C

Rationale: Rationale: C: Complement is produced by glial cells in the brain. This is true as glial cells secrete complement proteins to modulate immune responses in the brain. A: Complement is not released in an activated state but requires activation. B: Complement is activated by foreign molecules, not native proteins in the blood. D: Complement is part of the innate immune response, not just the adaptive immune response.