Which of the following is true regarding the proximal tubule?

Correct Answer: B

Rationale: Proximal tubule reabsorption is isosmotic water follows Na (e.g., ~65% reclaimed), maintaining osmolarity. Leaky epithelium is permeable false. Na uses transcellular/paracellular not only transcellular. Chloride rises in lumen drives later reabsorption. Isosmotic nature distinguishes it, key to bulk reabsorption, unlike permeability or ion errors.

Correct Answer: B

Rationale: Most enzymes function optimally at pH 7.4 physiological blood pH (e.g., neutral catalysis). 7.8 is alkalotic disrupts activity. 6.8 is acidic suboptimal. 2 is gastric extreme. Physiological pH distinguishes it, key to enzyme kinetics, unlike alkaline, acidic, or gastric values.

Correct Answer: C

Rationale: Respiratory isn't a chemical buffer physiological via COâ‚‚ excretion (e.g., lungs). Phosphate, bicarbonate, and proteins are chemical bind H directly. Respiratory's physiological role distinguishes it, key to system classification, unlike chemical buffers.

Correct Answer: B

Rationale: Kidneys, ureters, bladder, and urethra form the urinary system not liver/gallbladder (digestive), stomach/intestines (GI), or pancreas/spleen (endocrine/digestive). This lists core components, key for urine production/excretion, contrasting with non-urinary organs.

Correct Answer: A

Rationale: Aldosterone retains Na+ and excretes K+ not glucose (insulin), oxygen (lungs), or protein (liver). This specifies electrolyte control, critical for blood pressure, contrasting with unrelated functions.