Select Board & Class


Excretory Products and their Elimination

Excretory System In Humans (Group B)



  • Removal of nitrogenous wastes from the body

Nitrogenous wastes

  • Ammonia

    • Most toxic

    • Needs more water for getting excreted

    • Diffuses across general body surfaces

    • Examples of organisms excreting ammonia: fishes, aquatic amphibians and aquatic insects

    • Such organisms are called ammonotelic.

  • Urea

    • Less toxic

    • Requires less water for excretion

    • Terrestrial adaptation for conservation of water

    • Ammonia Urea

    • Examples of organisms excreting urea: terrestrial amphibians and marine fishes

    • Such organisms are called ureotelic.

  • Uric acid

    • Least toxic

    • Eliminated with the least loss of water, as pellets or paste

    • Examples of organisms excreting uric acid: birds, reptiles, land snails and insects

    • Such organisms are called uricotelic.

Human excretory system

It comprises of: 

i. pair of kidneys

ii. pair of ureters

iii. urinary bladder

iv. urethra

  • Kidney is divided into outer cortex and inner medullary region.

  • Nephrons are basic functional units of kidney.



  • Kidneys

    • Location: Between levels of the last thoracic and the third lumbar vertebra

    • Measurement: 10−12 cm (length) × 5−7 cm (width) × 2−3 cm (thickness)

    • Weight: 120−170 g

    • Hilum: A notch present towards the centre of the inner concave surface of the kidney

    • Through the hilum, the ureter, blood vessels and nerves enter the kidney.

    • On the inside of the hilum, the renal pelvis is present. Renal pelvis has projections called calyces.

    • 2 zones in the kidney: Cortex (outer)
      Medulla (inner)

    • Medulla divides into medullary pyramids (cone-shaped). These medullary pyramids project into the calyces.

    • Cortex is present in between the medullary pyramids as renal columns called the columns of Bertini.

    • Each kidney consists of about 1 million nephrons. These are the structural and functional units of the kidneys.



  • A Nephron has two parts:

    • Glomerulus

    • Renal tubule

  • Glomerulus

    • Tuft of capillaries formed by the afferent arteriole

  • Renal Tubule: Has many parts
    Bowman’s capsule Proximal Convoluted Tubule (PCT) Hair…

To view the complete topic, please

What are you looking for?