Which is NOT an action of CCK?

Correct Answer: B

Rationale: The correct answer is B: increased gastric motility and emptying. Cholecystokinin (CCK) is a hormone that primarily functions to stimulate gallbladder contraction (A), secretion of pancreatic juice (D), and inhibit gastric motility and emptying. Choice C, glucagon secretion, is not directly related to the actions of CCK. The incorrect choices (A, C, D) are all actions associated with CCK, while choice B goes against the typical action of CCK on gastric motility.

Correct Answer: D

Rationale: The correct answer is D because blood from the islets of Langerhans drains into the hepatic portal vein. This is important for the regulation of blood glucose levels by allowing insulin and glucagon produced by the islets to reach the liver directly. Choice A is incorrect because D cells secrete somatostatin, not pancreatic polypeptide. Choice B is incorrect as beta cells, not A cells, are the most common in the islets. Choice C is incorrect as the islets are most plentiful in the tail of the pancreas.

Correct Answer: C

Rationale: The correct answer is C because the substrates of the flavoprotein-cytochrome system are pyruvate, water, oxygen, and ATP. Pyruvate is oxidized to produce energy in the form of ATP, water is a byproduct of the electron transport chain, and oxygen is the final electron acceptor. Choices A and B are incorrect because cytochrome oxidase is not the first step in the chain, and the system does not occur within the endoplasmic reticulum. Choice D is incomplete.

Correct Answer: C

Rationale: The correct answer is C because steroid hormones are lipid-soluble and can diffuse through cell membranes. Once inside the cell, they bind to specific receptors in the cytoplasm. This hormone-receptor complex then enters the nucleus to regulate gene expression. Option A is incorrect because steroid hormone receptors are not found on nutrient molecules like glucose. Option B is incorrect as these receptors are not typically located in the interstitial fluid. Option D is also incorrect because steroid hormone receptors are not located on the cell membranes of target tissues.

Correct Answer: B

Rationale: Step-by-step rationale for why choice B (thyroid hormone) is correct: 1. Thyroid hormone is a key hormone that regulates metabolism and growth. 2. Intracellular hormone receptors are specific to certain hormones. 3. Disruption of thyroid hormone levels can lead to metabolic disorders. 4. Pesticide binding to the thyroid hormone receptor can interfere with its normal function. Summary of why other choices are incorrect: A: Melatonin regulates sleep-wake cycles, not metabolism. C: Growth hormone regulates growth and development, not metabolism. D: Insulin regulates blood sugar levels, not metabolism.