Excretory Products and Their Elimination

When your bladder fills up, smooth muscles contract while the urethral sphincter relaxes, letting urine flow out. This process is called micturition (or peeing!), and the nerves controlling it form the micturition reflex 🧠.

Fun urine facts 💛:

  • Adults make 1–1.5 liters of urine daily.
  • It’s light yellow, slightly acidic (pH ~6.0), and has a distinct smell.
  • Contains 25–30 grams of urea per day.
  • Urine tests help diagnose diseases. For example:
    • Glucose in urine (Glycosuria) → May indicate diabetes.
    • Ketone bodies in urine (Ketonuria) → Also hints at diabetes.

Other Organs That Help with Excretion

Kidneys aren’t the only heroes! Lungs, liver, and skin pitch in too:

  • Lungs 💨: Remove CO2 (~200 mL/min) and water vapor.
  • Liver 🦠: Secretes bile (with bilirubin, cholesterol, hormones, etc.) that leaves with poop.
  • Skin 💦:
    • Sweat glands: Release water, NaCl, urea, and lactic acid. Cools you and removes waste!
    • Sebaceous glands: Oily sebum carries sterols, waxes, and hydrocarbons.

(Psst: Even saliva removes tiny bits of nitrogenous waste! 😮)

Disorders of the Excretory System

When kidneys malfunction, trouble brews:

  • Uremia ⚠️: Urea builds up in blood → can cause kidney failure.
  • Hemodialysis (artificial kidney) to the rescue!
    • Blood is pumped from an artery into a dialysing unit.
    • A cellophane tube filters out nitrogenous wastes into dialysing fluid.
    • Clean blood returns to a vein 💉.
  • Kidney transplantation 🏥: Replaces failed kidneys. Donors (ideally close relatives) reduce rejection risk.
  • Renal calculi : Kidney stones made of crystallized salts (e.g., oxalates).
  • Glomerulonephritis 🔥: Inflammation of kidney filters (glomeruli).

Quick Summary

  • Animals excrete nitrogenous waste (ammonia, urea, or uric acid) based on habitat 💧.
  • Excretory organs (kidneys, nephridia, etc.) remove waste and balance body fluids.
  • Human excretory system: 2 kidneys → 2 ureters → bladder → urethra.
  • Each kidney has ~1 million nephrons (functional units).
  • Nephron parts:
    • Glomerulus (capillary tuft)
    • Renal tubule (Bowman’s capsule → PCT → Henle’s loop → DCT → collecting duct).
  • Urine formation involves:
    1. Filtration: Glomerulus filters blood (125 mL/min filtrate made).
    2. Reabsorption: Useful stuff (glucose, ions) taken back from tubules.
    3. Secretion: Extra wastes added to urine in tubules.

NEET Must-Knows 💡

  1. Micturition reflex: How bladder control works.
  2. Urine formation steps: Filtration, reabsorption, secretion.
  3. Hemodialysis: Artificial kidney function (urea removal).
  4. Other excretory organs: Roles of lungs, liver, and skin.
  5. Disorders: Uremia, renal calculi (stones), glomerulonephritis.

Keep going — you’re nailing this! 👏