Which of the following does NOT represent a possible source of input for the internal body pool?

Correct Answer: C

Rationale: Renal function does not represent a possible source of input for the internal body pool because it refers to the excretory system's function of filtering waste and excess substances from the blood, rather than introducing substances into the body. Inhalation introduces gases or particles into the body through the respiratory system. Intravenous injection delivers substances directly into the bloodstream. Absorption through the skin allows substances to enter the body through the skin barrier. Renal function involves filtering and eliminating substances from the body, making it the only choice that does not add to the internal body pool.

Correct Answer: B

Rationale: The correct answer is B (25 percent) because plasma constitutes around 20-25% of extracellular fluid. Plasma is the liquid component of blood and is part of the extracellular fluid. Option A (0 percent) is incorrect because plasma does make up a percentage of extracellular fluid. Option C (50 percent) and Option D (75 percent) are incorrect as they overestimate the percentage of extracellular fluid that plasma constitutes. Plasma, while important, is only a portion of the extracellular fluid in the body.

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.