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The Excretory System

Excretion and its importance

  • 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) Hairpin-shaped Loop of Henle Distal Convoluted Tubule (DCT) Collecting duct Medullary pyramids → Renal pelvis

Glomerulus + Bowman’s Capsule = Malpighian body (Renal Corpuscle)

  • Afferent arteriole:  These are the arterioles that arise from renal arteries and break into numerous capillaries to form glomerulus present inside the Bowman's capsule
  • Efferent arteriole: These are formed from the reunion of capillaries emerging from the Bowman's capsule. Once form…

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