The enteric plexus in the tunica submucosa is called the ______ plexus.

Correct Answer: A

Rationale: The correct answer is A: Meissner's plexus. Meissner's plexus is located in the tunica submucosa and is responsible for controlling the movements of the muscularis mucosae. It regulates local blood flow, secretion, and absorption in the small intestine. Auerbach's plexus, located in the muscularis externa, controls the motility of the muscular layer. Myenteric plexus is another name for Auerbach's plexus. Solar plexus is a network of nerves located in the abdomen, not specifically related to the enteric plexus.

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: C

Rationale: The correct answer is C: duodenum. The pancreas and liver release their secretions, such as pancreatic enzymes and bile, into the duodenum. This is because the duodenum is the first part of the small intestine where digestion primarily occurs. The stomach (A) is responsible for initial digestion of food, while the ileum (B) and jejunum (D) are parts of the small intestine where absorption of nutrients occurs, not secretion release.

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.