How Kidneys Make Concentrated Urine
🔑 The Counter Current System
Henle’s loop and vasa recta work together like a teamwork super-system:
- 💧 Opposite flows: Filtrate in Henle’s loop limbs moves in opposite directions
- 🧂 Salty medulla: Osmolarity increases from cortex (300 mOsmol/L) → inner medulla (1200 mOsmol/L) due to NaCl & urea
- 🔄 How it works:
- Ascending Henle’s limb pumps out NaCl → enters vasa recta
- Urea leaks from collecting duct → recycled in medulla
- 🚰 Result: Pulls water from collecting duct → makes super-concentrated urine (4× concentrated!)
⚖️ Hormonal Control of Kidneys
Your body’s remote control for kidneys:
- 🚨 ADH (Anti-diuretic Hormone):
- Released when body is dehydrated
- Makes kidneys reabsorb MORE water → less pee
- Also tightens blood vessels → ↑ blood pressure
- 🧂 Renin-Angiotensin System:
- Triggered when blood pressure/GFR drops
- Renin → Angiotensin I → Angiotensin II
- Angiotensin II:
- Squeezes blood vessels → ↑ BP
- Signals adrenal gland: “Release aldosterone!”
- Aldosterone → kidneys reabsorb Na⁺ & water
- 💖 ANF (Atrial Natriuretic Factor):
- Released when heart senses too much blood
- Widens blood vessels → ↓ BP
- Balances the renin system
🚽 Peeing Process (Micturition)
- 🧠 Bladder stretches when full → nerves signal brain
- 📨 Brain sends “time to go!” message
- 💪 You voluntarily relax muscles to pee
NEET Super-Important Concepts 💡
- Counter current multiplier: How Henle’s loop + vasa recta create medullary gradient
- ADH action: Water conservation during dehydration
- Renin-angiotensin-aldosterone axis: BP/GFR regulation
- ANF: Opposite player to renin system
- Osmolarity gradient: 300 → 1200 mOsmol/L from cortex to medulla
You’ve got this! Remember – kidneys are like smart water filters with hormone remote controls 🌊✨
