Vitamins are:

Correct Answer: C

Rationale: The correct answer is C because it accurately defines what vitamins are: essential organic substances needed in small amounts for normal growth and activity. Vitamins are obtained naturally from plant and animal foods. Choice A is incorrect because vitamins are organic, not inorganic. Choice B is incorrect because vitamins are needed in small quantities, not very large. Choice D is incorrect because vitamins are not products of endocrine gland secretion.

Correct Answer: A

Rationale: The correct answer is A: TRUE. Statins work by inhibiting HMG-CoA reductase, a key enzyme in cholesterol synthesis. This inhibition leads to upregulation of LDL receptors on hepatocytes, which increases the uptake of LDL cholesterol from the bloodstream, ultimately lowering LDL levels. Without LDL receptors, statins would not be effective. Choice B: FALSE is incorrect because statins do require LDL receptors for their mechanism of action. Choices C: All and D: None are not relevant in this context as the question is asking for a specific consideration regarding the mechanism of action of statins.

Correct Answer: D

Rationale: Step 1: Phosphorus is primarily excreted renally. Step 2: Calcitonin is a hormone that regulates calcium and phosphorus metabolism. Step 3: Calcitonin inhibits renal reabsorption of phosphorus. Step 4: Therefore, Calcitonin increases renal excretion of phosphorus. Step 5: This mechanism makes option D correct. Summary: A: Amiloride doesn't directly affect phosphorus excretion. B: Glucocorticoids affect calcium absorption, not phosphorus. C: Loop diuretics increase sodium and water excretion, not phosphorus.

Correct Answer: A

Rationale: Loop diuretics act by competitively blocking the Na+/K+/2Cl- cotransporter in the thick ascending limb of the loop of Henle. By inhibiting this transporter, loop diuretics prevent reabsorption of sodium, potassium, and chloride ions, leading to increased urine output. Thiazide diuretics work in the distal convoluted tubule by blocking the Na+/Cl- cotransporter. Potassium-sparing diuretics act on the collecting duct or distal tubule to inhibit sodium reabsorption and potassium secretion. Carbonic anhydrase inhibitors work in the proximal convoluted tubule by inhibiting the enzyme carbonic anhydrase, which reduces bicarbonate reabsorption. Therefore, the correct answer is A because loop diuretics specifically target the Na+/K+/2Cl- cotransporter in the loop of Henle.

Correct Answer: A

Rationale: The correct answer is A: Oxacillin. Oxacillin is penicillinase-resistant due to its side chain that protects it from penicillinase enzymes. This side chain confers resistance against beta-lactamase enzymes produced by certain bacteria. On the other hand, choices B, C, and D are not penicillinase-resistant. Amoxicillin and Penicillin G are susceptible to penicillinase enzymes, while Bicillin-5 is a combination of penicillin G and penicillinase-sensitive benzathine penicillin. Thus, Oxacillin is the only penicillinase-resistant drug among the options provided.