Which of these statements refers to osmolarity?

Correct Answer: D

Rationale: The correct answer is D because osmolarity refers to the concentration of solutes in a solution. A hypertonic solution has a higher concentration of solutes compared to an isotonic solution, leading to water moving out of cells through osmosis. This definition directly relates to osmolarity. A, B, and C are incorrect as they do not directly relate to osmolarity. Choice A talks about vasopressin secretion in response to water deficit, B discusses urinary output in dehydration, and C is incomplete. These choices do not address the concept of osmolarity, which is about solute concentration in a solution.

Correct Answer: B

Rationale: The correct answer is B because each bicarbonate ion can carry two H+ ions, which helps maintain the pH balance in the extracellular fluid (ECF). When there is an excess of H+ ions, bicarbonate ions bind with them to form carbonic acid, which then dissociates into water and carbon dioxide. This helps prevent drastic changes in pH by removing excess H+ ions. Choice A is incorrect because bicarbonate and carbonic acid levels are tightly regulated in the body. Choice C is incorrect because carbonic acid is a weak acid and does not dissociate easily. Choice D is incorrect because the abundance of bicarbonate and carbonic acid in the plasma alone does not make the buffering system effective; it is the ability of bicarbonate ions to carry H+ ions that makes it effective.

Correct Answer: C

Rationale: The correct answer is C: haemoglobin. Haemoglobin acts as a buffer for H+ generated from CO at the tissue level by binding to the H+ ions, preventing drastic changes in blood pH. Hemoglobin can also release H+ ions when needed, helping to maintain pH balance. A: The HCO3- buffer system primarily buffers H+ generated from CO2 at the tissue level, not from CO. B: The phosphate buffer system mainly functions in the kidneys to regulate blood pH, not in buffering H+ from CO. D: Plasma proteins have a limited role in buffering H+ compared to haemoglobin.

Correct Answer: A

Rationale: The correct answer is A: HCO3-. Tubular epithelial cells secrete bicarbonate ions (HCO3-) to buffer the secreted H+ ions. Bicarbonate acts as a base to neutralize the excess acidity in the filtrate. Choice B (OH-) is incorrect because hydroxide ions would only increase the pH, not buffer the acidity. Choice C (NH3) is incorrect because ammonia does not directly buffer acidity. Choice D (NH4+) is incorrect as it is a weak acid and would not effectively buffer the acidity of the filtrate.

Correct Answer: D

Rationale: Respiratory acidosis occurs when the lungs can't remove enough carbon dioxide, leading to an increase in blood acidity. Emphysema, choice D, a lung condition causing poor air exchange, can result in respiratory acidosis. Aspirin poisoning (choice A) typically causes metabolic acidosis. Severe vomiting (choice B) can lead to metabolic alkalosis due to loss of stomach acid. Severe diarrhea (choice C) can also cause metabolic acidosis from loss of bicarbonate. Therefore, the correct answer is D as it directly affects the respiratory system and can lead to respiratory acidosis.