Kidney Structure & Nephrons

🧠 Key parts of a nephron:

  • Afferent arteriole → brings blood into the glomerulus
  • Glomerulus → ball of capillaries where filtration starts
  • Bowman’s capsule → cups around glomerulus to collect filtrate
  • Proximal Convoluted Tubule (PCT) → first coiled tube after Bowman’s capsule
  • Henle’s loop → U-shaped with descending & ascending limbs
  • Distal Convoluted Tubule (DCT) → coiled tube after Henle’s loop
  • Collecting duct → collects urine from many nephrons

🔬 2 types of nephrons:

  • Cortical nephrons: Henle’s loop is short (mostly in outer kidney) 😊
  • Juxtamedullary nephrons: Henle’s loop is long (reaches deep into inner kidney) 🔍

How Urine is Formed (3 Steps!)

💦 1. Glomerular Filtration:

  • Blood enters glomerulus under high pressure
  • Water & small solutes (glucose, ions) get squeezed out like coffee through a filter ☕
  • Big stuff (proteins/blood cells) stay in blood → filtrate forms in Bowman’s capsule
  • GFR (Glomerular Filtration Rate) = 125 mL/min (That’s 180 L/day! 🌊)

↩️ 2. Reabsorption:

  • 99% of filtrate gets reclaimed! 🤯
  • Useful stuff (glucose, amino acids, \( \text{Na}^+ \), water) moves back into blood
  • Happens in tubules via active transport (needs energy) or passive transport (no energy)

🚽 3. Secretion:

  • Tubules add extra wastes to urine (like \( \text{H}^+ \), \( \text{K}^+ \), ammonia)
  • Helps control blood pH & ion balance ⚖️

What Each Tubule Does

TubuleFunctionSpecial Features
PCT
(Proximal Convoluted Tubule)		✨ Reabsorbs:
  • All nutrients (glucose/amino acids)
  • 70-80% water & electrolytes
✨ Secretes \( \text{H}^+ \), ammonia		Has brush border to maximize absorption! 🧽
Henle’s Loop ✨ Descending limb: Lets water out → filtrate gets concentrated 🔼
✨ Ascending limb: Pumps out \( \text{Na}^+ \)/Cl⁻ → filtrate gets dilute 🔽		Creates salty medulla for water conservation! 🧂
DCT
(Distal Convoluted Tubule)		 ✨ Reabsorbs \( \text{Na}^+ \), water as needed
✨ Secretes \( \text{K}^+ \), \( \text{H}^+ \), \( \text{NH}_3 \)
✨ Regulates blood pH & \( \text{Na}^+ \)/\( \text{K}^+ \) balance		Hormones control its work (e.g., aldosterone) 🎚️

🌟 NEET Must-Knows 🌟

  1. GFR = 125 mL/min → regulated by JGA (Juxtaglomerular Apparatus) & renin hormone when blood pressure drops ⬇️.
  2. 3 urine processes: Filtration (glomerulus) → Reabsorption (tubules) → Secretion (tubules).
  3. Henle’s loop → creates medullary concentration gradient for water absorption 💧.
  4. PCT → reabsorbs most nutrients/water; DCT → fine-tunes ion/pH balance.
  5. Cortical vs. Juxtamedullary nephrons: Only juxtamedullary have long loops + vasa recta for concentrated urine.

Keep going – you’re nailing kidney physiology! 💪🧠