Hypertonicity in the ECF is sensed by osmoreceptors in the hypothalamus.

Correct Answer: A

Rationale: The correct answer is A because osmoreceptors in the hypothalamus do sense changes in extracellular fluid (ECF) tonicity. When ECF becomes hypertonic, these osmoreceptors are activated, leading to the release of antidiuretic hormone (ADH) to increase water reabsorption and maintain body fluid balance. The other choices are incorrect as they do not provide any relevant information or reasoning.

Correct Answer: A

Rationale: Step 1: Acidosis leads to increased H+ excretion by the kidneys to help regulate blood pH. Step 2: In response to increased H+ excretion, there is a decrease in the excretion of K+ ions. Step 3: Reduced K+ excretion leads to K+ retention in the body. Therefore, the correct answer is A (TRUE). Acidosis does indeed cause the kidneys to excrete more H+, which in turn reduces the amount of K+ secreted, resulting in K+ retention. Option B is incorrect because it contradicts the physiological relationship between acidosis, H+ excretion, and K+ retention. Options C and D are not applicable as they are placeholders.

Correct Answer: A

Rationale: Step 1: Metabolic acidosis results from an increase in acid levels in the body due to a non-respiratory cause. Step 2: If metabolic acidosis is caused by a pulmonary disease, it implies that the respiratory system is already compromised. Step 3: When the respiratory system is affected by a pulmonary disease, its ability to buffer the acid-base imbalance is diminished. Step 4: Therefore, if metabolic acidosis is caused by a pulmonary disease, the respiratory system cannot effectively act as a buffering system. Summary: Choice A is correct because when a pulmonary disease causes metabolic acidosis, the respiratory system's buffering capacity is impaired. Choices B, C, and D are incorrect as they do not explain the relationship between pulmonary disease and metabolic acidosis.

Correct Answer: B

Rationale: The correct answer is B: FALSE. The kidneys are not the first line of defense against changes in acid-base balance; they are the second line of defense. The first line of defense is the buffer systems in the body, which include bicarbonate, phosphate, and proteins. These buffer systems act quickly to prevent drastic changes in pH. The kidneys come into play as a slower but more powerful mechanism for maintaining pH by regulating the excretion or retention of hydrogen ions and bicarbonate ions. Therefore, while the kidneys are crucial in long-term regulation of acid-base balance, they are not the first line of defense.

Correct Answer: B

Rationale: The correct answer is B: FALSE. The respiratory system can partially compensate for metabolic acidosis by increasing ventilation to eliminate excess CO2. However, it cannot completely compensate as it cannot directly regulate bicarbonate levels in the blood. The kidneys play a crucial role in fully compensating for metabolic acidosis by excreting hydrogen ions and reabsorbing bicarbonate. Choice A is incorrect because the respiratory system alone cannot fully compensate for metabolic acidosis. Choices C and D are not applicable as they do not provide any relevant information regarding the statement.