Which of the body's buffering systems is the first to counteract changes in pH?

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 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.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Calculate the ratio: [HCO3-] / [CO2] = 20/2 = 10 2. Normal ratio is 20/1, so a ratio of 10 indicates a decrease in HCO3-. 3. Decrease in HCO3- leads to increased acidity, indicating acidosis. 4. Since the issue is not related to CO2 levels, it is uncompensated respiratory acidosis. Summary: - Choice A is correct due to the low [HCO3-] / [CO2] ratio indicating acidosis. - Choices B, C, and D are incorrect as they do not match the given scenario of respiratory acidosis.

Correct Answer: C

Rationale: Rationale: The correct answer is C: chloride. The serum anion gap is calculated by subtracting the sum of bicarbonate and chloride from sodium. Chloride is the primary anion contributing to the serum anion gap, as it plays a crucial role in maintaining electrical neutrality. Phosphate (A) and bicarbonate (B) are not included in the calculation of the serum anion gap. Sodium (D) is a cation, not an anion, so it does not directly contribute to the anion gap. Therefore, chloride is the correct answer as it is a major anion contributing to the serum anion gap.

Correct Answer: B

Rationale: Step 1: The internal pool includes various substances like nutrients, waste products, and ions. Step 2: Substances can also be removed through metabolic processes like oxidation or conversion. Step 3: Excretion is not the sole method; other ways include sweat, breath, or shedding skin. Step 4: Therefore, the statement that excretion is the only way for substances to be removed from the internal pool is false.