Chapter 16: Excretory Products and Their Elimination – Part 1

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🚽 Chapter 16: Excretory Products and Their Elimination – Part 1

💧 Waste Management in Living Organisms

🧬 Why Excretion?

Metabolic reactions produce nitrogenous wastes, mainly from the breakdown of amino acids and nucleic acids. These wastes are toxic and must be removed to maintain homeostasis.

🧪 Types of Nitrogenous Wastes

Waste Product Description Examples
Ammonia (NH₃) Highly toxic, requires lots of water Fish, amphibians
Urea Less toxic, moderate water required Mammals, amphibians
Uric Acid Least toxic, excreted as paste/crystals Birds, reptiles, insects

🧠 This gives rise to:

  • Ammonotelic organisms – e.g., Bony fishes

  • Ureotelic organisms – e.g., Humans

  • Uricotelic organisms – e.g., Birds

🧍 Human Excretory System

The human excretory system primarily removes urea and involves:

✅ Main Excretory Organs:

Organ Function
Kidneys Filter blood, form urine
Ureters Transport urine to bladder
Urinary Bladder Stores urine temporarily
Urethra Expels urine out of the body

🧠 Kidneys in Detail

  • Bean-shaped organs

  • Location: Back of the abdominal cavity, one on each side of vertebral column

  • Length: ~10–12 cm, Width: ~5–7 cm

  • Right kidney is slightly lower than the left

🧱 Internal Structure of Kidney

  • Outer region: Cortex

  • Inner region: Medulla

  • Medulla has renal pyramids

  • Pyramids end in calyces, opening into renal pelvis

  • Nephrons: Structural & functional units of kidney

🔄 Blood Supply

  • Renal artery: Brings in oxygenated, waste-rich blood

  • Renal vein: Carries filtered blood back to circulation

🔬 Nephron – The Functional Unit

Each kidney has about 1 million nephrons.

Structure of a Nephron:

  1. Bowman’s Capsule:

    • Cup-shaped structure

    • Surrounds a network of capillaries called the Glomerulus

    • Site of ultrafiltration

  2. Renal Tubule:

    • Proximal Convoluted Tubule (PCT): Reabsorption of nutrients, ions, water

    • Loop of Henle: Hairpin-shaped; descending & ascending limbs

    • Distal Convoluted Tubule (DCT): Selective secretion & reabsorption

    • Collecting Duct: Collects urine from multiple nephrons

Types of Nephrons

Type Location Role
Cortical Nephrons In cortex Most nephrons, shorter loop
Juxtamedullary Nephrons Near medulla Long Loop of Henle, concentrate urine

🧠 NEET PYQs – Basics of Excretion

  1. Which is the chief nitrogenous waste in humans?
    A) Ammonia
    B) Uric acid
    C) Urea
    D) Creatinine
    ✅ Answer: C) Urea

  2. The structural and functional unit of kidney is:
    A) Glomerulus
    B) Nephron
    C) Loop of Henle
    D) Bowman’s capsule
    ✅ Answer: B) Nephron

  3. Juxtamedullary nephrons help in:
    A) Secretion of ADH
    B) Producing dilute urine
    C) Producing concentrated urine
    D) Reabsorption of glucose
    ✅ Answer: C) Producing concentrated urine

💡 Quick Facts Recap

  • Excretion removes nitrogenous waste to maintain internal balance.

  • Humans are ureotelic.

  • Nephron: key player in urine formation.

  • Two types of nephrons: cortical (short) & juxtamedullary (long).

  • Loop of Henle plays a big role in water conservation.

📘 Boost your NEET Biology prep here:


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