Human Excretory System Notes 🌟

🧩 What Makes Up the System?

Your excretory system includes:

  • 2 kidneys (bean-shaped, reddish-brown)
  • 2 ureters (tubes)
  • 1 urinary bladder (storage sac)
  • 1 urethra (exit tube)

🎯 Kidney Details

Location & Size:

  • Sit near the back of your belly, between the last rib and lower spine
  • Each is 10-12 cm long, 5-7 cm wide, and weighs 120-170 g

Internal Structure:

  1. Hilum: Notch where ureters, blood vessels and nerves enter
  2. Renal pelvis: Funnel-shaped space inside hilum with cup-like calyces
  3. Zones:
    • Cortex (outer layer)
    • Medulla (inner layer with cone-shaped medullary pyramids)
  4. Renal columns: Cortex extensions between pyramids (called Columns of Bertini)

🧬 Nephrons: The Tiny Filters

Each kidney has ~1 million nephrons! They clean blood and make urine.

Parts of a Nephron:

  1. Glomerulus 🌪️: Bundle of capillaries (from afferent arteriole). Blood leaves via efferent arteriole
  2. Renal Tubule:
    • Bowman’s capsule: Cup around glomerulus
    • Proximal Convoluted Tubule (PCT): Twisty tube
    • Loop of Henle: Hairpin loop (descending + ascending limbs)
    • Distal Convoluted Tubule (DCT): More twists!
    • Collecting duct: Drains into renal pelvis

Glomerulus + Bowman’s capsule = Malpighian body (or renal corpuscle) 💡

⚖️ 2 Types of Nephrons

  1. Cortical Nephrons:
    • Loop of Henle is short
    • Stays mostly in cortex
    • No (or tiny) vasa recta (capillaries around loop)
  2. Juxtamedullary Nephrons:
    • Loop of Henle is long and dips deep into medulla
    • Has vasa recta (U-shaped capillaries around loop)

💦 How Urine is Made (Step 1)

Glomerular Filtration:

  • Blood enters glomerulus under high pressure
  • Water, salts and small molecules squeeze into Bowman’s capsule
  • Filtration layers:
    • Capillary walls
    • Basement membrane
    • Podocyte cells (with filtration slits)
  • 🚫 Proteins stay in blood (too big to pass)
  • 1100-1200 ml blood filtered every minute! (That’s \( \frac{1}{5} \) of blood pumped by your heart!)

📚 NEET Super-Important Concepts!

  1. Nephron Structure 🌈:
    • Know all parts (glomerulus, PCT, loop of Henle, DCT, collecting duct)
    • Cortical vs. juxtamedullary nephrons
  2. Glomerular Filtration 🔍:
    • Layers involved (capillaries, basement membrane, podocytes)
    • Filtered fluid = plasma minus proteins
  3. Kidney Anatomy 🗺️:
    • Cortex, medulla, pyramids, calyces, renal pelvis
    • Columns of Bertini