Which of the following contributes the vast majority of the extracellular fluid's osmotic activity?

Correct Answer: B

Rationale: The correct answer is B: plasma proteins. Plasma proteins contribute the vast majority of extracellular fluid's osmotic activity due to their high concentration and large size, which results in significant osmotic pressure. This osmotic pressure helps maintain fluid balance and regulate the movement of water between compartments. Na+ and its attendant anions (Choice A) are important for fluid balance but do not contribute significantly to osmotic activity. K+ and its attendant anions (Choice C) are mainly intracellular ions and do not play a major role in extracellular osmotic activity. Ca2+ and its attendant anions (Choice D) are essential for various cellular functions but do not contribute significantly to extracellular osmotic activity.

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: B

Rationale: The correct answer is B: disorientation and coma. Acidosis occurs when the body's pH level becomes too acidic. This leads to central nervous system dysfunction, resulting in disorientation and potentially coma. Extreme nervousness (A) is not a typical symptom of acidosis. "Pins and needles" sensations (C) are more commonly associated with nerve damage or circulation issues. Muscle twitches and spasms (D) are not specific to acidosis and can occur due to various reasons. In summary, disorientation and coma are key indicators of acidosis due to the impact on the central nervous system.

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.