How does the renin-angiotensin-aldosterone system promote an increase in arterial blood pressure?

Correct Answer: C

Rationale: The correct answer is C because the renin-angiotensin-aldosterone system promotes an increase in arterial blood pressure by promoting Na+ reabsorption in the distal and collecting tubules. This leads to an increase in blood volume and subsequently an increase in blood pressure. The other choices are incorrect because: A: Water reabsorption through vasopressin release does not directly contribute to an increase in arterial blood pressure. B: The baroreceptor reflex helps regulate blood pressure by sensing changes and triggering appropriate responses, but it does not directly promote an increase in arterial blood pressure. D: Vasodilation of the afferent arteriole and increasing glomerular filtration rate actually lead to a decrease in blood pressure by reducing resistance in the kidneys.

Correct Answer: B

Rationale: Correct Answer: B (Ca2+) Rationale: In states of acidosis, the body retains Ca2+ in body fluids to help buffer the excess H+ ions and maintain pH balance. Ca2+ acts as a buffer by binding to excess H+ ions, reducing acidity. Kidneys increase Ca2+ retention to counteract the increased H+ secretion. This relationship helps stabilize the body's pH. Summary: A: Na+ is not directly involved in buffering excess H+ ions during acidosis. C: K+ is not specifically retained in response to increased H+ secretion. D: Cl- is not directly related to buffering and pH balance in acidosis.

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.