Human Excretory System

  • Excretion - Excretion is the removal of the metabolic wastes of an organism. Wastes that are removed include carbon dioxide, water, salt, urea and uric acid. All excreted wastes travel at some time in the blood.
  • Organs of the Excretory System
  1. Lungs - removal of excess carbon dioxide
  2. Liver - produces urea and uric acid as a by-product of the breakdown of proteins
  3. Skin - removal of excess water, salt, urea and uric acid
  4. Urinary System - kidneys filter the blood to form urine, which is excess water, salt, urea and uric acid

The Skin

Two Layers of the Skin

  1. Epidermis - outer protective layer without blood vessels
  2. Dermis - inner layer containing blood vessels, sensory nerve endings, sweat and oil glands, hairs, and fat cells

Functions of the Skin

  1. Excretion - Wastes such as excess water, salt, urea and uric acid are removed from the body in sweat.
  2. Waterproofing - The skin with its oil glands prevents the entry of water into, and loss of water out of the body.
  3. Protection from Disease - The intact skin prevents invasion of micro-organisms and dust into the body.
  4. Protection from Ultraviolet Rays - Pigments reduce the intake of UV rays.
  5. Regulation of Body Temperature - The thin layer of fat cells in the dermis insulates the body. Contraction of small muscles attached to hairs forms 'goose bumps' and creates an insulating blanket of warm air. Also, sweat produced by sweat glands uses excess body heat to evaporate, providing a cooling effect.
  6. Sensory Detection - The nerve endings or receptors in the dermis detect heat, cold, touch, pressure and pain.

The Urinary System

Urine

Parts of the Urinary System

Urinary System Diagram




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