The nephron is the structural and functional unit of the kidney responsible for urine formation through ultrafiltration, selective reabsorption, and tubular secretion. It is important for NEET Biology because NTA frequently tests nephron anatomy, GFR values, the countercurrent mechanism, and the roles of hormones like ADH and aldosterone in urine concentration.
Bowman’s Capsule
Cup-shaped structure that encloses the glomerulus and collects the filtrate during ultrafiltration.
Glomerulus
Tuft of capillaries where blood is filtered under high pressure to form glomerular filtrate.
Afferent Arteriole
Brings blood into the glomerulus; wider diameter maintains high glomerular pressure.
Efferent Arteriole
Carries filtered blood away from the glomerulus; narrower diameter keeps filtration pressure high.
PCT (Proximal Convoluted Tubule)
Reabsorbs ~80% of filtrate including glucose, amino acids, Na⁺, and water by active and passive transport.
Loop of Henle — Descending Limb
Permeable to water but not solutes; concentrates filtrate as it descends into the medulla.
Loop of Henle — Ascending Limb
Impermeable to water; actively pumps out NaCl to create the medullary concentration gradient.
DCT (Distal Convoluted Tubule)
Fine-tunes urine composition through selective reabsorption of Na⁺ and secretion of K⁺ and H⁺ under hormonal control.
Collecting Duct
Final water reabsorption site regulated by ADH; carries concentrated urine to the renal pelvis.
Ultrafiltration (GFR)
NTA tests GFR value (125 mL/min), factors affecting filtration, and the role of afferent vs efferent arteriole diameter. Know that filtration is a non-selective, pressure-driven process.
Selective Reabsorption
Expect questions on which substances are reabsorbed where — glucose and amino acids in PCT (obligatory reabsorption), water in descending limb, NaCl in ascending limb. Active vs passive transport distinction is frequently tested.
Countercurrent Mechanism
NTA asks how the Loop of Henle and vasa recta maintain the medullary osmotic gradient. Descending limb loses water, ascending limb pumps NaCl — this creates the gradient for urine concentration.
Tubular Secretion
Questions on secretion of H⁺, K⁺, and NH₃ in DCT and collecting duct. Know the role of aldosterone (Na⁺ reabsorption, K⁺ secretion) and ADH (water reabsorption in collecting duct).
Master nephron structure, filtration, reabsorption and secretion with previous year questions that match NTA's exact patterns.