Which of the following hormones is produced by the adrenal cortex?

Correct Answer: A

Rationale: The correct answer is A: Aldosterone. The adrenal cortex is responsible for producing aldosterone, a hormone that regulates blood pressure and electrolyte balance. Aldosterone is specifically produced in the zona glomerulosa layer of the adrenal cortex. Adrenaline (Choice B) is produced by the adrenal medulla, not the cortex. Glucagon (Choice C) is produced by the pancreas, not the adrenal cortex. Calcitonin (Choice D) is produced by the thyroid gland, not the adrenal cortex. Therefore, the correct answer is A because aldosterone is the hormone produced by the adrenal cortex.

Correct Answer: A

Rationale: The correct answer is A because blood vessels in the gut are primarily innervated by sympathetic and parasympathetic fibers, not by enteric nerves. Enteric nerves are confined to the gastrointestinal tract itself and are responsible for regulating gut motility, secretion, and blood flow. Sympathetic innervation typically causes vasoconstriction, while parasympathetic innervation promotes vasodilation. The myenteric plexus (Auerbach's plexus) lies between the longitudinal and circular muscle layers, regulating gut motility. Parasympathetic supply to the gut is mainly through the vagus nerve (cranial nerve X) and sacral nerves (pelvic splanchnic nerves). Sympathetic supply can either be inhibitory or excitatory, but generally, sympathetic fibers are inhibitory on cholinergic postganglionic fibers in the gut.

Correct Answer: C

Rationale: The correct answer is C: theophylline. Theophylline stimulates insulin secretion by increasing cAMP levels in pancreatic beta cells, leading to enhanced insulin release. Thiazide diuretics (A) can actually reduce insulin secretion. Phenytoin (B) and beta blockers (D) are known to inhibit insulin secretion. Therefore, theophylline is the only choice that directly stimulates insulin secretion.

Correct Answer: D

Rationale: Correct Answer: D - The conversion of pyruvate to acetyl-CoA is irreversible because it is catalyzed by the enzyme pyruvate dehydrogenase. This step is a key regulatory point in carbohydrate metabolism as it commits pyruvate to enter the citric acid cycle for further energy production. Reversing this step would disrupt the normal flow of metabolic pathways. Summary of other choices: A: Glucokinase is not increased in starvation; it regulates glucose uptake in the liver. B: The breakdown of glycogen is called glycogenolysis, not glycolysis which is the breakdown of glucose. C: The direct oxidative pathway involves the breakdown of glucose through glycolysis, not triose.

Correct Answer: C

Rationale: The correct answer is C: Thyroid. The thyroid gland is located at the base of the throat, just inferior to the laryngeal prominence. It is responsible for producing hormones that regulate metabolism and growth. The pituitary gland (A) is located in the brain and controls other endocrine glands. The hypothalamus (B) is also in the brain and regulates hormone production. The pineal gland (D) is located in the brain and produces melatonin. Thyroid is correct due to its anatomical location and function in hormone regulation.