All of the following statements concerning vitamin A functions are true EXCEPT:

Correct Answer: D

Rationale: The correct answer is D because vitamin A does not act as a hormone involved in the regulation of calcium and phosphorus homeostasis. A: This statement is true as vitamin A is essential for the transmission of light stimuli to the brain through the formation of visual pigment in the retina. B: This statement is true as retinoic acid, a metabolite of vitamin A, plays a crucial role in regulating cell growth and differentiation in various tissues. C: This statement is true as retinoic acid is important during embryogenesis for proper development. In summary, vitamin A is not involved in the regulation of calcium and phosphorus homeostasis, making statement D the correct answer.

Correct Answer: C

Rationale: The correct answer is C: Colchicine. Colchicine is used in the treatment of gout by preventing the migration of granulocytes to the inflamed area, thereby reducing inflammation and pain. Allopurinol (A) works by reducing uric acid production, Sulfinpyrazone (B) and Indomethacin (D) work by inhibiting uric acid reabsorption and reducing inflammation through prostaglandin inhibition, respectively. These mechanisms do not involve preventing the migration of granulocytes.

Correct Answer: D

Rationale: The correct answer is D because all the statements are true about calcium. A: The recommended daily allowances for calcium intake vary with age groups. B: Calcium chloride can indeed be irritating and cause necrosis if it leaks out of the vein during intravenous administration. C: Patients with achlorhydria (lack of stomach acid) may have decreased calcium absorption, so calcium carbonate is recommended to be taken with meals or switching to calcium citrate for better absorption. Therefore, choice D encompasses all the correct statements about calcium, making it the correct answer.

Correct Answer: C

Rationale: Thiazide diuretics are used in the treatment of recurrent calcium nephrolithiasis by reducing urinary calcium excretion. They work by increasing calcium reabsorption in the kidneys, lowering calcium levels in urine, and decreasing the formation of kidney stones. Osmotic diuretics (A) increase urine output but do not specifically target calcium excretion. Loop diuretics (B) inhibit sodium reabsorption but can increase urinary calcium excretion and are not ideal for treating calcium nephrolithiasis. Potassium-sparing diuretics (D) primarily affect potassium and sodium levels and do not directly impact calcium excretion.

Correct Answer: C

Rationale: The correct answer is C: Pseudomembranous colitis. Lincozamides, like clindamycin, can disrupt the normal gut flora, leading to overgrowth of Clostridium difficile and causing pseudomembranous colitis. This condition is characterized by severe diarrhea, abdominal pain, and potentially life-threatening complications. Nephrotoxicity (A) is not a common side effect of lincozamides. Cancerogenity (B) is not associated with lincozamides. Irritation of respiratory organs (D) is not a typical adverse effect of this drug class.