Fluid exiting the proximal convoluted tubule is maximally concentrated in which filtrate constituent?
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Answer: C. Nitrogenous waste
Explanation
As filtrate passes through the proximal tubule, useful substances are reabsorbed, concentrating wastes. Water and nutrients leave the tubule lumen, leaving nitrogenous waste products highly concentrated. Nitrogenous waste becomes maximally concentrated because water and solutes are selectively removed upstream. The proximal convoluted tubule is the initial segment of the renal nephron tubular system. Epithelial cells lining this tubule actively transport glucose, amino acids, and ions out of filtrate. Urea and other nitrogenous wastes remain inside the tubule as water follows solute reabsorption.
Efficient kidney function relies on selective reabsorption to retain vital nutrients while excreting metabolic toxins. Renal pathologies can impair proximal tubule function, leading to abnormal loss of nutrients in urine. Blood filtration is a continuous physiological process required to maintain internal chemical homeostasis. Glucose is almost completely reabsorbed in the proximal convoluted tubule rather than left concentrated. Essential amino acids are also reclaimed by transport proteins and returned directly to the bloodstream. The option including all of these is incorrect because glucose and amino acids are reabsorbed.
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