What is the most important long-term regulator of blood pressure?

Correct Answer: B

Rationale: The correct answer is B: urinary output by the kidneys. The kidneys play a crucial role in regulating blood pressure by adjusting the volume of blood in circulation through the control of water and electrolyte balance. Increased urinary output decreases blood volume, leading to a decrease in blood pressure, while decreased urinary output increases blood volume and blood pressure. This long-term regulation mechanism helps maintain blood pressure within a normal range over time. A: the baroreceptor reflex is a short-term regulator that responds to acute changes in blood pressure. C: shifting of fluid between interstitial fluid and plasma may affect blood volume temporarily but is not the primary long-term regulator of blood pressure. D: the thirst mechanism regulates fluid intake to maintain hydration but does not directly regulate blood pressure.

Correct Answer: C

Rationale: To calculate how many times more acidic a pH of 4 is compared to a pH of 7, we use the formula 10^(pH difference). In this case, the pH difference is 7-4 = 3. Therefore, 10^3 = 1000. So, a pH of 4 is 1000 times more acidic than a pH of 7. Choice A (10) is incorrect because it represents a pH difference of 1, not 3. Choice B (100) is incorrect as it represents a pH difference of 2. Choice D (10,000) is incorrect as it represents a pH difference of 4.

Correct Answer: A

Rationale: The correct answer is A: chemical buffering systems. Chemical buffering systems are the first to counteract changes in pH because they work instantly by releasing or absorbing hydrogen ions to maintain pH balance. Renal buffering systems and respiratory buffering systems take longer to respond to pH changes as they involve processes like kidney excretion or breathing rate adjustments. Choice D is incorrect because different buffering systems do not all work at the same speed due to their varying mechanisms and response times.

Correct Answer: C

Rationale: The primary buffer system in the intracellular fluid (ICF) is bicarbonate/carbonic acid. This system helps maintain the pH balance within cells by neutralizing any excess acids or bases. Bicarbonate acts as a weak base, while carbonic acid acts as a weak acid, allowing them to buffer changes in pH effectively. Haemoglobin (choice A) primarily functions as an oxygen carrier in the blood. Phosphate (choice B) is a buffer system in the urine and plays a role in buffering pH in the renal system. Proteins (choice D) can act as buffers in the blood, but they are not the primary buffer system in the ICF. Therefore, the correct choice is C as it directly relates to the primary buffer system within the intracellular fluid.

Correct Answer: C

Rationale: The correct answer is C: PO 3- secretion. The kidneys regulate pH by either excreting H+ ions or reabsorbing HCO3- ions. NH3 secretion helps in buffering H+ ions, while HCO3- excretion helps in regulating blood pH. PO 3- secretion does not directly affect pH regulation in the extracellular fluid. Hence, it is not modified by the kidneys to regulate pH.