The major natural progestin is:

Correct Answer: C

Rationale: Step-by-step rationale for why choice C (Progesterone) is correct: 1. Progesterone is a major natural progestin produced by the corpus luteum in the ovaries. 2. It plays a crucial role in the menstrual cycle and maintaining pregnancy. 3. Estradiol (choice A), Estron (choice B), and Estriol (choice D) are all estrogens, not progestins. 4. Estradiol is a predominant estrogen in premenopausal women, while Estron and Estriol are less potent estrogens. 5. Therefore, the correct answer is choice C, Progesterone, as it is the primary natural progestin in the body.

Correct Answer: B

Rationale: The correct answer is B: Immunosuppressive agents. Tacrolimus (FK-506) belongs to this class as it suppresses the immune system. It is commonly used in transplant patients to prevent organ rejection by inhibiting T-cell activation. Immunoglobulins (A) are antibodies produced by the immune system. Interferons (C) are signaling proteins released by cells in response to pathogens. Monoclonal antibodies (D) are antibodies produced by identical immune cells and used for targeted therapies. Therefore, the most appropriate classification for tacrolimus is as an immunosuppressive agent due to its mechanism of action and therapeutic use in modulating the immune response.

Correct Answer: A

Rationale: Step 1: Identify the antienzyme that inhibits proteolysis. Proteolysis is the breakdown of proteins into smaller peptides or amino acids by proteolytic enzymes. Step 2: Contrical is a proteolysis inhibitor that specifically inhibits trypsin, a digestive enzyme that breaks down proteins in the small intestine. Step 3: Sulbactam is a beta-lactamase inhibitor used in combination with antibiotics to prevent bacterial resistance. Step 4: Aminocaproic acid is a fibrinolysis inhibitor used to prevent excessive blood clot breakdown. Step 5: Disulfiram is an alcohol deterrent that inhibits aldehyde dehydrogenase, not proteolysis. Summary: Contrical (Choice A) is the correct answer as it directly inhibits a proteolytic enzyme involved in protein breakdown. Sulbactam, aminocaproic acid, and disulfiram do not target proteolysis enzymes.

Correct Answer: B

Rationale: Rationale: 1. Probucol does not stimulate the rate of clearance of LDL by receptor-mediated pathways. 2. Probucol works by increasing HDL levels and reducing LDL oxidation. 3. Therefore, the statement that Probucol stimulates LDL clearance is false. 4. Choice B is correct as it accurately reflects the mechanism of action of Probucol. Summary: - Choice A is incorrect as Probucol does not stimulate LDL clearance. - Choice C is incorrect as not all statements are true. - Choice D is incorrect as the statement is false.

Correct Answer: A

Rationale: Step-by-step rationale for correct answer (A): 1. Dihydrotachysterol is a vitamin D analog used to treat parathyroid hormone resistance. 2. Parathyroid hormone resistance leads to impaired calcium absorption and bone mineralization. 3. Dihydrotachysterol helps increase calcium absorption and bone mineralization in these patients. Summary of incorrect choices: - B: Paget's disease is typically treated with bisphosphonates or calcitonin, not dihydrotachysterol. - C: Increased osteolysis is not a direct indication for dihydrotachysterol administration. - D: Hypophosphatemia is usually treated with phosphate supplements, not dihydrotachysterol.