Red blood cells lack mitochondria. As a result, ATP production is solely through

A. Urine concentration and volume are determined by countercurrent mechanisms: The countercurrent multiplier (nephron loop) and countercurrent exchanger (vasa recta) help establish a medullary osmotic gradient that allows for urine concentration or dilution.
B. The kidneys produce a large volume of dilute urine when overhydrated: In overhydration, ADH secretion is suppressed, leading to reduced water reabsorption and a larger volume of dilute urine.
C. The concentration of urine is lower when urine volume is reduced: This is incorrect. When urine volume is reduced (e.g., dehydration), the urine is more concentrated, not less.
D. The kidneys produce a small volume of concentrated urine when dehydrated: In dehydration, ADH is secreted, causing increased water reabsorption, resulting in concentrated urine with low volume.

A. Buffered hydrogen ions are excreted in urine: This process allows new bicarbonate ions to enter the plasma, helping correct acidosis.
B. Glutamine is metabolized by deamination, oxidation, and acidification: Glutamine metabolism in renal tubule cells generates ammonia and bicarbonate, contributing to acid-base balance.
C. Ammonium ions are excreted in urine: Excreting ammonium (NH₄⁺) removes H⁺ from the body and indirectly adds new bicarbonate to the plasma.
D. Bicarbonate ions are reclaimed by tubular reabsorption: This does not generate new bicarbonate-it simply prevents loss of existing bicarbonate, which is important but not a replenishing mechanism during depletion.