Excretory System - Urinary System - Excretion

Life of every organism depends on certain basic processes. Excretion is one among them. Different organisms follow different modes of excretion. In complex organisms including humans, there is a specialized system for excretion called excretory system. Let us go through the excretory system and modes of excretion in animals.


As a result of cellular respiration, there are lots of gaseous and other forms of waste products that are produced within the body. These waste products need to be removed as they are toxic to the body. Excretion is the process of elimination of wastes produced within a body. Various systems in our body help in excretion such as kidney, lungs, skin, eyes, etc. Different animals eliminate waste in different forms depending on their habitat and food habit.

For example, aquatic animals excrete waste in the form of ammonia while birds and insects excrete mainly uric acid. Humans have urea as the major excretory product.


We know the fact that blood transports food, air, and water to different parts of the body. It also carries waste products. The human body consists of a specialized system which purifies the blood. This system is known as excretory system. An excretory system comprises of,

  • A pair of kidneys
  • A pair of ureters
  • Urinary bladder
  • Urethra

    Human Excretory System

    Human Excretory System

Blood contains both useful and harmful substances. Hence, we have kidneys which separate useful substances by reabsorption and toxic substances by forming urine. Capillaries (a type of blood vessel) of kidneys filter the blood. All needful substances will be reabsorbed back into body and waste materials will be converted into urine. Urine thus formed will be passed to urinary bladder via ureter. Through the urinary opening at urethra, we excrete urine.

Other than the urinary system, skin, lungs, and even eyes help us to excrete waste products in different forms. Sweating is a type of excretion where water, urea, and other salts are excreted through the skin. Lungs help us to exhale gaseous wastes such as carbon dioxide, nitrogen, etc.

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The basic functional unit of human kidney is