Why is the bicarbonate/carbonic acid buffering system a very effective system for the ECF?

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: 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.

Correct Answer: A

Rationale: The correct answer is A: phosphate buffer system. Phosphate buffer system is an important intracellular buffer that helps regulate pH within cells. It consists of dihydrogen phosphate (H2PO4-) and monohydrogen phosphate (HPO4^2-). When [H+] increases, H2PO4- can accept H+ ions to form H3PO4, preventing a drastic decrease in pH. Choice B (NH4+:NH3 buffer system) is incorrect because it primarily functions in the kidney to regulate acid-base balance. Choice C (protein buffer system) is incorrect because proteins mainly act as intracellular buffers and have a limited capacity to respond to rapid changes in [H+]. Choice D (haemoglobin buffer system) is incorrect because haemoglobin primarily buffers CO2 levels in the blood through the bicarbonate buffer system, not [H+].

Correct Answer: A

Rationale: The correct answer is A. When the ingestion and metabolic synthesis of a substance equal its metabolic utilization and excretion, the body is in a state of balance, known as homeostasis. This means that the body is efficiently utilizing and eliminating the substance to maintain equilibrium. Option B is incorrect because in this scenario, the body is indeed in balance, not in imbalance. Options C and D are also incorrect as they do not provide any relevant information or reasoning. In summary, the correct answer (A) reflects a state of equilibrium in the body's metabolic processes, while the other choices do not accurately describe the situation.