Verapamil has a significant effect on automaticity in the SA node It’s:

Correct Answer: A

Rationale: Verapamil is a calcium channel blocker that slows the influx of calcium ions in cardiac cells, leading to a decrease in automaticity in the SA node. This results in a decrease in heart rate. Therefore, choice A is correct. Choice B is incorrect because verapamil does affect automaticity. Choices C and D are incorrect as they do not accurately reflect the specific effect of verapamil on automaticity in the SA node.

Correct Answer: D

Rationale: Step-by-step rationale for why choice D is correct: 1. Growth hormone stimulates the synthesis or release of somatomedins, supporting statement A. 2. Low levels of IGF-1 are associated with dwarfism, validating statement B. 3. Hypersecretion of growth hormone can lead to acromegaly, confirming statement C. 4. Choice D is incorrect because growth hormone is contraindicated in subjects with open epiphyses, not closed ones. This is because GH can stimulate bone growth, potentially causing issues in individuals with open growth plates.

Correct Answer: D

Rationale: The correct answer is D because the statement that the half-life of glucagon is between 6 and 8 hours is FALSE. Glucagon's half-life is actually very short, around 5-10 minutes. This is due to rapid degradation by enzymes in the liver and kidneys. Glucagon is not stable in the bloodstream for long periods. A: Statement A is true as glucagon is indeed synthesized in the A cells of the pancreatic islets of Langerhans. B: Statement B is true as glucagon is a peptide consisting of a single chain of 29 amino acids, which is conserved across mammals. C: Statement C is true as glucagon is extensively degraded in the liver, kidneys, plasma, and at tissue receptor sites.

Correct Answer: C

Rationale: The correct answer is C: Celecoxib. Celecoxib is a selective COX-2 inhibitor, meaning it primarily targets the COX-2 enzyme, reducing inflammation and pain without affecting the protective COX-1 enzyme. This selective action reduces the risk of gastrointestinal side effects associated with traditional NSAIDs that inhibit both COX-1 and COX-2. Piroxicam (A), Indomethacin (B), and Diclofenac (D) are non-selective NSAIDs that inhibit both COX-1 and COX-2, leading to a higher risk of gastrointestinal complications.

Correct Answer: B

Rationale: The correct answer is B: Cyclosporine. Cyclosporine is an immunosuppressant medication used to prevent organ rejection after transplantation. It is not considered a cytotoxic agent because it does not directly target and kill rapidly dividing cells. Azathioprine, Leflunomide, and Cyclophosphamide are cytotoxic agents commonly used in chemotherapy to kill rapidly dividing cells, making them incorrect choices.