Which of the following factors does NOT determine body water content?

Correct Answer: C

Rationale: The correct answer is C: ethnicity. Body water content is primarily determined by physiological factors, such as sex, age, and body composition. Ethnicity does not directly affect body water content as it is not a physiological factor. Sex can influence body water content due to hormonal differences, age affects it due to changes in body composition and metabolism, and body composition, such as muscle mass and fat percentage, can also impact body water content. Therefore, ethnicity is the factor that does NOT determine body water content.

Correct Answer: A

Rationale: The correct answer is A: plasma membrane. This is because the plasma membrane is a selectively permeable barrier that separates the extracellular fluid (ECF) outside the cell from the intracellular fluid (ICF) inside the cell. It regulates the movement of substances in and out of the cell, maintaining the internal environment of the cell. Choice B (blood-brain barrier) is incorrect as it specifically refers to a barrier within the brain that regulates the passage of substances between the blood and the brain tissue, not between ECF and ICF. Choice C (blood vessel walls) is incorrect as blood vessel walls primarily regulate the exchange of substances between the blood and tissues, not between ECF and ICF. Choice D (transcellular membrane) is incorrect as it is not a commonly recognized term in cell biology. The term transcellular transport refers to the movement of substances across a cell, which is facilitated by various cellular structures including the plasma membrane.

Correct Answer: C

Rationale: The correct answer is C: salt balance. Salt balance is crucial for maintaining extracellular fluid (ECF) volume as salt, specifically sodium, plays a key role in regulating fluid balance in the body. When salt intake is high, the body retains more water to maintain osmotic balance, increasing ECF volume. On the other hand, low salt intake can lead to decreased ECF volume due to water loss. Vasopressin secretion (A) regulates water reabsorption in the kidneys, not salt balance. Free water balance (B) is important but does not directly impact ECF volume maintenance. Potassium balance (D) is more relevant to intracellular fluid balance and membrane potential, not ECF volume regulation.

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: 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.