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Class 11 Biology Notes: Excretory Products and Their Elimination | NCERT Summary, Human Kidney, Nephron, Urine Formation, Hormonal Regulation, Disorders


Overview: Chapter – Excretory Products and Their Elimination





1. Types of Nitrogenous Wastes


Animals excrete three main types:


Ammonia – excreted by ammonotelic organisms like aquatic animals; highly toxic, requiring large water quantities .


Urea – excreted by ureotelic organisms such as mammals (including humans), amphibians; less toxic and water-efficient .


Uric acid – excreted by uricotelic organisms like birds, reptiles, insects; least toxic and conserves water .




2. Human Excretory System


Composed of kidneys, ureters, urinary bladder, and urethra .


Functional units in kidneys are nephrons—each kidney has about 1 million .



3. Urine Formation Mechanisms


Glomerular filtration – filters blood into Bowman’s capsule (protein-free fluid) .


Tubular reabsorption – reclaims needed substances.


Tubular secretion – removes excess ions, ammonia, etc. .



4. Countercurrent Mechanism


The loop of Henle and vasa recta create osmotic gradients in the medulla (300 to 1200 mOsmol/L), allowing concentration of urine .



5. Regulation of Kidney Function


ADH (Antidiuretic Hormone) – increases water reabsorption in collecting ducts.


Aldosterone – promotes sodium reabsorption and water retention.


Renin-Angiotensin System – adjusts blood pressure and glomerular filtration rate (GFR) .



6. Other Excretory Organs & Systems


Lungs: expel CO₂ and water vapor.


Skin: eliminate water, salts, urea (via sweat).


Liver: detoxifies, converts ammonia to urea, excretes pigments and cholesterol .



7. Excretory Structures in Other Organisms


Contractile vacuoles in amoeba/paramecium.


Canal systems in sponges; coelenteron in Hydra.


Flame cells (protonephridia) in flatworms.


Nephridia in annelids (like earthworms).


Green glands in prawns.


Malpighian tubules in insects and other arthropods .



8. Common Excretory Disorders


Urinary tract infections (UTIs)


Kidney stones (renal calculi)


Kidney failure (renal insufficiency)


Glomerulonephritis .



Summary Table


Topic Key Points


Excretory Waste Types Ammonia (ammonotelic), Urea (ureotelic), Uric acid (uricotelic)

Human Excretory Organs Kidneys, ureters, bladder, urethra

Urine Formation Filtration, reabsorption, secretion

Countercurrent Mechanism Concentrates urine via Henle’s loop and vasa recta

Regulation ADH, aldosterone, RAAS, GFR adjustment

Other Excretory Organs Lungs, skin, liver

Non-Human Excretory Systems Contractile vacuoles, flame cells, nephridia, green glands, Malpighian tubules

Disorders UTIs, kidney stones, kidney failure, glome rulonephritis





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