The thirst centre is closely related to, or perhaps identical to, the cells that secrete vasopressin.

Correct Answer: A

Rationale: The correct answer is A. The thirst center is indeed closely related to the cells that secrete vasopressin. When the body is dehydrated, the thirst center in the brain is activated, leading to the release of vasopressin, a hormone that helps regulate water balance by promoting water reabsorption in the kidneys. This close relationship between the thirst center and vasopressin-secreting cells highlights their interconnected roles in maintaining proper hydration levels in the body. Choices B, C, and D are incorrect as they do not provide a logical explanation or reasoning behind the relationship between the thirst center and vasopressin-secreting cells.

Correct Answer: A

Rationale: The phosphate buffering system works in the kidney and is effective in regulating blood pH. The bicarbonate buffering system operates in the blood and helps maintain acid-base balance. Both systems are important for buffering extracellular fluid. Other choices are incorrect because they do not provide a valid response to the question.

Correct Answer: B

Rationale: Rationale: The major source of H+ in the body fluids is not carbonic acid from CO2, but rather metabolic processes generating H+ ions directly or through the dissociation of other acids. CO2 is converted to carbonic acid as part of the bicarbonate buffer system, which helps regulate pH but is not the primary source of H+ ions. Therefore, option B is correct. Option A is incorrect as explained above. Options C and D are not applicable as they are not choices related to the question.

Correct Answer: A

Rationale: The correct answer is A because the statement aligns with the physiological process of renal compensation in response to increased acidity in the body. The kidneys secrete more H+ ions and conserve HCO3- to help maintain the body's pH within a normal range. This process helps to regulate acid-base balance. Choice B is incorrect because it contradicts the known function of the kidneys in maintaining acid-base balance. Choices C and D are not applicable as they do not provide any relevant information to address the question.

Correct Answer: A

Rationale: The correct answer is A: TRUE. H+ secretion is coupled to bicarbonate reabsorption in the renal tubules. This process occurs in the proximal tubule of the nephron, where H+ ions are secreted into the tubular lumen in exchange for reabsorption of bicarbonate ions. This mechanism helps regulate blood pH by maintaining a balance between acid and base in the body. Other choices (B, C, D) are incorrect as they do not provide a valid explanation or relevant information related to the process of H+ secretion and bicarbonate reabsorption in the kidneys.