Glomerulus, arterioles, vasa rectaCollecting duct: aquaporin-2 set by ADHUrine, deeper as it concentratesOne long-looped human nephron laid out on a board that stands for the kidney in section (ruler: 1 tick = 1 mm). Segment lengths are true (proximal tubule 14 mm, loop limbs 10 mm, collecting duct 20 mm); tubes and capsule are drawn ~15× wide. Each dot is 1% of the filtrate, and the kidneys filter 180 L a day. Water leaves where it really does: two thirds in the proximal tubule, ~15% in the descending limb, none in the ascending limb, which pumps out salt and builds the medulla's gradient (300 → 1200 mOsm/kg, left ruler and darkening bands). The last ~18% meets the collecting duct, and ADH decides how much of it returns: none (urine ~18 L/day, 50 mOsm/kg) to almost all (~0.5 L/day, 1200 mOsm/kg). Reabsorbed water passes to the peritubular capillaries. Flow is shown ~40× faster, at relative rates.
180 L/day两肾每天滤过的原尿（GFR 125 ml/min）filtered by both kidneys (GFR 125 ml/min)~1.5 L/day通常的尿量，滤液的 ~1%usual urine output, ~1% of filtrate67%近端小管重吸收的水water reabsorbed in the proximal tubule0.5–18 L/dayADH 从最大到为零时的尿量urine from maximal to no ADH50–1200 mOsm/kg尿渗透压范围urine osmolality range~1 million每个肾的肾单位数nephrons per kidney