Adaptive (acquired) immunity refers to:

Correct Answer: B

Rationale: The correct answer is B because adaptive immunity is characterized by antigen-specific defense mechanisms that target and eliminate specific pathogens. This type of immunity takes time to develop, usually several days, and involves the activation of lymphocytes such as T and B cells that can recognize and respond to specific antigens. This process leads to the formation of memory cells that provide long-lasting protection against future encounters with the same antigen. Choices A, C, and D are incorrect: A: This describes innate (natural) immunity, which is present at birth and provides immediate, nonspecific defense mechanisms against pathogens. C: Interferons are signaling proteins produced in response to viral infections and are part of the innate immune response, not adaptive immunity. D: Immunosuppressive agents are drugs that suppress the immune system and are used to prevent rejection of transplanted organs or treat autoimmune diseases. They do not enhance adaptive immunity.

Correct Answer: A

Rationale: Physostigmine is the correct answer as it is a cholinesterase inhibitor. Cholinesterase inhibitors prevent the breakdown of acetylcholine, leading to increased cholinergic activity. Physostigmine specifically inhibits both acetylcholinesterase and butyrylcholinesterase. This action results in increased levels of acetylcholine in the synaptic cleft, enhancing cholinergic transmission. This mechanism is used in the treatment of conditions such as myasthenia gravis and glaucoma. Selegiline (B) is a monoamine oxidase inhibitor used in the treatment of Parkinson's disease. Aminocaproic acid (C) is an antifibrinolytic agent used to treat excessive bleeding. Disulfiram (D) is an alcohol deterrent used in the management of alcohol dependence by inhibiting aldehyde dehydrogenase. These choices are incorrect as they do not act as cholinesterase inhibitors.

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.