Regulation of Kidney Function

Your kidneys are smartly controlled by hormones from your brain, heart, and a special kidney area called the JGA (juxtaglomerular apparatus)! Here’s how:

🩸 Antidiuretic Hormone (ADH) System

  • When your body loses too much fluid (e.g., sweating), osmoreceptors in your blood detect this.
  • They alert your brain (hypothalamus), which releases ADH.
  • ADH helps your kidneys reabsorb water 💧 from urine-in-making, so you produce less urine (prevents dehydration!).
  • ADH also tightens blood vessels → raises blood pressure → boosts kidney filtration (GFR).
  • When body fluids increase, ADH stops. It’s a feedback loop!

⚖️ Renin-Angiotensin System (JGA’s Role)

  • If blood pressure/filtration drops, JG cells release renin.
  • Renin converts angiotensinogen (a protein) → Angiotensin I → Angiotensin II.
  • Angiotensin II:
    • Squeezes blood vessels → ↑ blood pressure & GFR.
    • Triggers aldosterone release from adrenal glands.
  • Aldosterone makes kidneys reabsorb Na⁺ and water → ↑ blood volume & pressure.

💓 Atrial Natriuretic Factor (ANF) – Heart’s Role

  • When too much blood flows to the heart’s atria, they release ANF.
  • ANF widens blood vessels → lowers blood pressure.
  • It opposes the renin system to keep balance!

Micturition (Peeing!)

  • Urine from nephrons is stored in the bladder 🎈.
  • When full, the bladder stretches → activates stretch receptors.
  • Receptors signal the brain (CNS), which sends back:
    • “Squeeze!” to bladder muscles
    • “Relax!” to the urethral sphincter (exit door)
  • This reflex is called the micturition reflex.
  • Fun fact: Adults make 1-1.5 liters of urine/day!

💛 Urine Characteristics

  • Color: Light yellow
  • pH: Slightly acidic (~6.0)
  • Smell: Distinct odor
  • Contains: 25-30 g urea/day
  • Urine tests help diagnose diseases:
    • Glucose in urine (Glycosuria) → Diabetes
    • Ketones in urine (Ketonuria) → Diabetes

Other Excretory Organs

🌬️ Lungs

  • Remove CO₂ (200 mL/min!) & water vapor.

🧴 Liver

  • Secretes bile containing wastes:
    • Bilirubin/biliverdin (from old blood cells)
    • Cholesterol, drugs, hormones
  • Exits via poop 💩.

💦 Skin

  • Sweat glands: Release water, NaCl, urea, lactic acid. Cools you + removes waste!
  • Sebaceous glands: Release oils (sebum) with sterols & waxes → protects skin.
  • Psst… saliva also removes a bit of nitrogenous waste!

Excretory Disorders

⚠️ Uremia

  • Caused by kidney failure → urea piles up in blood.
  • Treated with hemodialysis (artificial kidney):
    • Blood from artery → dialysis machine.
    • Machine filters urea using dialysing fluid.
    • Blood returns to vein (with anticoagulants like heparin).

🌟 NEET Must-Knows

  1. ADH & Osmoregulation: How ADH conserves water during dehydration.
  2. Renin-Angiotensin-Aldosterone: How low BP triggers this hormone cascade.
  3. ANF vs. Renin: Opposing roles in BP control (ANF ↓BP, Renin ↑BP).
  4. Micturition Reflex: CNS role in bladder control.
  5. Urine Analysis: Glycosuria/Ketonuria = Diabetes clues.