Excretion in Living Organisms

Excretion in Organisms

• Waste materials result from food metabolism in unicellular and multicellular organisms.
• Accumulation of waste causes toxicosis and obstructs biological functions, necessitating excretion.
• Excretion balances the cells and environment while regulating water and salt levels.

Types of Excretion in Humans

• Digestive Excretion:

  • Involves the expulsion of feces, comprising undigested food, water, bacteria, and dead cells from the digestive tract.

• Pulmonary Excretion:

  • Carbon dioxide and water vapor are expelled through the respiratory system.

• Renal Excretion:

  • Excess water and harmful substances, such as urea, are filtered from the blood by the urinary system.

• Skin Excretion:

  • The skin eliminates excess water, salts, urea, and small amounts of carbon dioxide.

Structure of the Urinary System

• The urinary system carries out renal excretion, primarily involving the kidneys.

• Kidneys:

  • There are two bean-shaped kidneys located on either side of the vertebral column in the abdominal cavity.
  • Each kidney is surrounded by a thin membrane called the capsule.
  • Kidneys consist of two main layers:

    • Cortex:

      • The outer layer, red in color, containing microscopic filtering units known as nephrons.

    • Medulla:

      • The inner part, bright-colored and striped, housing many urinary tubules.
      • Contains the renal pelvis, which is the cavity at the center and the starting point of the ureter.

• Circulation:

  • Renal arteries supply blood to the kidneys, while renal veins remove waste products.