Critical Numerical Values
| Parameter | Value | Significance |
|---|---|---|
| GFR (Glomerular Filtration Rate) | 125 mL/min | Volume of plasma filtered per minute |
| Daily filtrate volume | 180 L/day | 125 mL/min × 60 min × 24 hr ÷ 1000 |
| Daily urine volume | ~1.5 L/day | Only ~0.83% of filtrate excreted |
| % filtrate reabsorbed | ~99% | By tubular reabsorption |
| PCT reabsorption | ~65–70% of filtrate | Largest single site of reabsorption |
| Nephrons per kidney | ~1 million (10^6) | Structural/functional units |
| Kidney dimensions | 10–12 cm long | Bean-shaped, retroperitoneal |
| Medullary osmolarity (cortex) | 300 mOsm/L | Iso-osmotic with plasma |
| Medullary osmolarity (inner medulla) | 1200 mOsm/L | Maximum achievable in humans |
| Plasma osmolarity | ~300 mOsm/L | Normal blood osmolarity |
| Urine osmolarity (maximum) | ~1200 mOsm/L | With maximum ADH |
| Urine osmolarity (minimum) | ~50–100 mOsm/L | Without ADH |
| Cortical nephrons | ~85% | Short loop; limited concentration role |
| Juxtamedullary nephrons | ~15% | Long loop; key for concentrated urine |
Key Calculations
- GFR calculation: GFR = (Urine creatinine × Urine flow rate) / Plasma creatinine
- Daily filtrate = 125 mL/min × 1440 min/day = 180,000 mL = 180 L
- % reabsorbed = (180 − 1.5) / 180 × 100 = 99.2% ≈ 99%
- If plasma creatinine doubles → GFR halved (inverse relationship)