Which hormone is most important in insulin secretion?

Correct Answer: C

Rationale: The correct answer is C: GIP (glucose-dependent insulinotropic peptide). GIP is an incretin hormone released from the small intestine in response to glucose ingestion, stimulating insulin secretion from pancreatic beta cells. Gastrin (A), CCK (B), and secretin (D) are gastrointestinal hormones that do not directly influence insulin secretion. GIP plays a crucial role in regulating blood sugar levels by promoting insulin release, making it the most important hormone in insulin secretion.

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.

Correct Answer: C

Rationale: The correct answer is C: neural. In this scenario, the student experiences the fight or flight response, which is controlled by the sympathetic nervous system. The pupil dilation, increased heart rate, and rapid breathing are all physiological responses triggered by the activation of neural pathways in response to a perceived threat or stress. The other choices are incorrect because: A: Humoral stimuli involve changes in blood levels of certain substances triggering hormone release. B: Hormonal stimuli involve the release of hormones in response to other hormones. D: Positive feedback is a mechanism that amplifies a response, not directly related to the immediate physiological responses seen in this case.