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NEET Biology Excretory Products and their Elimination

Excretory Products and Their Elimination PDF Notes, Important Questions and Synopsis




  • Excretion is the process by which living organisms get rid of waste substances either totally or partially accumulated during metabolic activities.

  • Modes of Excretion in Animals

  • Organs of Excretion in Animals

    Animal group

    Excretory structures


    • Contractile vacuole


    • Body surface


    • Body surface


    • Protonephridia or flame cells


    • Nephridia


    • Tube feet and dermal branchiae

  • Urine Formation

  • Counter Current Mechanism

    • In the two limbs of the loop of Henle, urine flows in the opposite direction which forms a 
    • counter current.
    • Similarly, the flow of blood in the two limbs of the vasa recta are also in the counter current pattern.
    • This system of a liquid flowing in the two limbs in two opposite directions is termed the counter 
    • current mechanism.
    • It helps to maintain the concentration gradient in the renal medulla and hence helps in concentrating urine in the loop of Henle.

  • Regulation of Kidney Function

    Myogenic Autoregulation

    Neural Control Hormonal Control
    • When the systemic blood pressure increases, the afferent arteriole narrows down which decreases GFR.

    • Nerve fibres of the sympathetic nervous system innervate the blood vessels of the kidneys which decreases GFR.
    • Anti-diuretic hormone (ADH)
    • Renin
    • Atrial natriuretic factor (ANF)

  • The process of release of urine is called micturition.

  • Role of Other Excretory Organs

    Sweat glands

    • Excrete sweat


    • Remove carbon dioxide and water vapour


    •  Eliminates cholesterol, inactivated products of steroid hormones, vitamins and drugs

    Large intestine

    • Removes salts such as calcium phosphate