Gastric juices in the stomach:

Correct Answer: D

Rationale: Step 1: Gastric juices contain hydrochloric acid, which helps in the breakdown of food and kills bacteria. Step 2: The combination of different enzymes in gastric juices works together to digest food effectively. Step 3: Therefore, the correct answer is D, as gastric juices in the stomach both kill bacteria and work together to digest food. Summary: - Choice A is incorrect because gastric juices do more than just killing bacteria. - Choice B is incorrect because gastric juices not only digest food but also kill bacteria. - Choice C is incorrect because gastric juices do more than just contain hydrochloric acid.

Correct Answer: B

Rationale: The correct answer is B: submucosa. The submucosa is the layer of the gastrointestinal tract that contains tough, fibrous connective tissue, providing support and elasticity. The mucosa (choice A) is the innermost layer responsible for absorption, not toughness. The muscle layer (choice C) is responsible for peristalsis and movement, not toughness. The serosa (choice D) is the outermost layer providing protection, not toughness. Therefore, choice B is the correct answer as it accurately describes the layer characterized by tough, fibrous connective tissue in the gastrointestinal tract.

Correct Answer: B

Rationale: The correct answer is B: lipids. Cholecystokinin (CCK) is released in response to the presence of lipids in the duodenum. When lipids are detected, CCK is secreted by the enteroendocrine cells in the small intestine. CCK plays a crucial role in the digestion and absorption of lipids by stimulating the release of bile from the gallbladder and pancreatic enzymes. Explanation for why the other choices are incorrect: A: Chyme is a mixture of partially digested food and gastric juices. While chyme may contain lipids, it is not the specific stimulus for CCK release. C: Protein stimulates the release of other hormones like gastrin and secretin, not CCK. D: Gastrin is a hormone that stimulates gastric acid secretion, not CCK release in response to lipids.

Correct Answer: B

Rationale: The correct answer is B: cystic. The common bile duct is formed by the merger of the hepatic duct from the liver and the cystic duct from the gallbladder. The cystic duct carries bile from the gallbladder to the common bile duct, which then transports bile to the small intestine. Choices A, C, and D are incorrect because the common bile duct is not formed by the merger of the common hepatic, pancreatic, or Santorini ducts. Each of these ducts serves a different function in the digestive system.

Correct Answer: B

Rationale: Correct Answer: B: intrinsic factor Rationale: 1. Intrinsic factor is essential for the absorption of vitamin B12 in the ileum. 2. Parietal cells secrete intrinsic factor in the stomach. 3. Without intrinsic factor, vitamin B12 cannot be absorbed, leading to pernicious anemia. Summary of Incorrect Choices: A: Hydrochloric acid is also secreted by parietal cells but is not directly involved in vitamin B12 absorption. C: Pepsinogen is a precursor to pepsin, which is involved in protein digestion, not vitamin B12 absorption. D: Mucus protects the stomach lining and does not play a role in vitamin B12 absorption.