Read What the Tubules Return and Remove
The nephron modifies filtrate by reclaiming useful materials and secreting selected ions and wastes.
Tubular Processing and Urine Formation is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Reabsorb along the tubule
The PCT reabsorbs the largest share of water and electrolytes and normally all filtered glucose and amino acids. Reabsorption can be active or passive. The descending loop concentrates filtrate; distal segments adjust sodium and water according to hormonal signals.
Secrete and calculate
Tubular secretion of H+, K+ and ammonia supports ionic and acid–base balance.
Roughly 99% of filtrate is returned to blood.
Map nephron segments to function
Ultrafiltration occurs at the renal corpuscle. The proximal convoluted tubule reabsorbs most filtered glucose and amino acids; the ascending limb creates a diluting tubular fluid, while ADH changes water permeability in the collecting duct.
Review tubular reabsorption and secretion
The proximal convoluted tubule reabsorbs most filtered water and electrolytes and essentially all glucose and amino acids under normal conditions. Tubular secretion of H⁺, K⁺ and ammonia supports ionic and acid–base balance. Excretion follows filtration − reabsorption + secretion; active and passive processes both contribute to reabsorption.
OlympIQ exam lens
- ✓PCT: largest bulk reabsorption; glucose/amino acids normally fully reabsorbed.
- ✓Tubular transport uses active and passive mechanisms.
- ✓Excretion = GF − TR + TS.
Secretion is added to the filtrate; reabsorption is subtracted from filtered load.
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