Top 10 Must-Know Facts
- GFR = 125 mL/min → 180 L filtrate/day → 99% reabsorbed → ~1.5 L urine/day.
- Nephrons per kidney = ~1 million. Cortical (85%) = short loop. Juxtamedullary (15%) = long loop (for concentrated urine).
- Descending limb = water-permeable, solute-impermeable. Ascending limb = NaCl-permeable, water-impermeable.
- Medullary gradient: 300 mOsm/L (cortex) to 1200 mOsm/L (inner medulla).
- PCT reabsorbs 65–70% of filtrate: glucose, amino acids, Na+, water (obligatory osmosis). Also secretes H+, NH3, K+.
- ADH → water reabsorption in DCT + collecting duct.
- Aldosterone (adrenal cortex) → Na+ reabsorption + K+ secretion in DCT (RAAS effector).
- ANF (cardiac atria) → decreases Na+ reabsorption → opposes aldosterone. Trigger = high blood volume.
- RAAS sequence: Low BP → Renin (JG cells) → Angiotensin I → ACE → Angiotensin II → Aldosterone.
- Ornithine cycle (urea synthesis) occurs in the LIVER, not the kidney.
Top 5 Critical Values
| Value | Fact |
|---|---|
| 125 mL/min | GFR in healthy adult |
| 180 L/day | Daily filtrate volume |
| ~1.5 L/day | Daily urine volume (only ~0.83% of filtrate) |
| 99% | Percentage of filtrate reabsorbed |
| 1,000,000 (10^6) | Nephrons per kidney |
Top 3 NEET Traps
- Frog trap: Adult frog = ureotelic; tadpole = ammonotelic. Marine fish = ureotelic (NOT ammonotelic).
- Loop permeability trap: Descending = water-permeable; ascending = NaCl-permeable. Students swap these — use the D=Drinks water, A=Allows salts out mnemonic.
- GFR vs urine trap: GFR produces 180 L/day filtrate, NOT urine. Urine = 1.5 L/day (99% reabsorbed). Never select 180 L as the urine output answer.