What will happen if the osmolarity of ECF increases?

Correct Answer: A

Rationale: Step 1: Increased ECF osmolarity causes osmoreceptors to detect the change. Step 2: Osmoreceptors signal the hypothalamus to release ADH (vasopressin). Step 3: ADH increases water reabsorption in the kidneys. Step 4: Water shifts from the ICF into the ECF to restore osmotic balance. Therefore, choice A is correct. Choices B and C are incorrect because changes in osmolarity trigger water movement. Choice D is incorrect because vasopressin secretion would actually increase to help restore water balance.

Correct Answer: C

Rationale: The primary buffer system in the extracellular fluid (ECF) is the bicarbonate/carbonic acid system. This system helps maintain the pH of the blood within a narrow range by accepting or releasing hydrogen ions. Carbonic acid can donate hydrogen ions to lower pH, while bicarbonate can accept hydrogen ions to raise pH. Haemoglobin primarily functions as an oxygen transporter in the blood and does not play a significant role as a buffer in the ECF. Chloride/hydrochloric acid is more involved in the stomach's acidic environment and is not a primary buffer system in the ECF. Phosphate is a buffer system mainly found in the intracellular fluid and urine, not in the ECF. Therefore, option C is the correct answer as it is the primary buffer system in the ECF, while the other options are not as directly involved in maintaining the ECF pH balance.

Correct Answer: C

Rationale: Haemoglobin is the main buffer for O2. It binds to oxygen in the lungs and releases it in tissues. This buffering action helps maintain a stable oxygen-carrying capacity in the blood. Choices A, B, and D are incorrect as haemoglobin does not primarily buffer PO3-, CO4^2-, or NO. These molecules do not have a direct relationship with haemoglobin's oxygen-carrying function.

Correct Answer: A

Rationale: The correct answer is A because sympathetic activity does not directly regulate renal secretion of H+. Sympathetic activity mainly affects blood flow and blood pressure regulation in the kidneys. In contrast, choices B, C, and D all describe factors that do influence the regulation of renal H+ secretion. B explains how respiratory dysfunction can trigger increased H+ secretion, C emphasizes the role of CO levels in determining H+ secretion, and D points out that elevated plasma [H+] leads to increased renal H+ secretion. Therefore, A is the only option that does not accurately describe how renal secretion of H+ is regulated.

Correct Answer: A

Rationale: Metabolic acidosis occurs when the body produces too much acid or fails to remove enough acid. Aspirin poisoning can lead to metabolic acidosis by increasing the production of lactic acid and impairing the kidney's ability to excrete acid. Severe vomiting and severe diarrhea can cause metabolic alkalosis due to loss of stomach acid or bicarbonate, respectively. Emphysema is associated with respiratory acidosis due to impaired gas exchange, not metabolic acidosis. Therefore, the correct answer is A (aspirin poisoning).