• Organisms carry out biochemical reactions to produce energy.
  • These biochemical reactions taking place in the body may produce toxic wastes, which if accumulated may harm the organism.
  • Thus, the process of removal of toxic wastes from the body is important. This removal is called Excretion .


The biological process by which the harmful wastes containing nitrogen are removed from the body is called excretion .


Major waste products produced in the Human body: 

(1) Carbon Dioxide: 

Produced as a waste by the oxidation of food during respiration.

It is removed by lungs .


(2) Urea:

It is produced as a waste by the decomposition of unused proteins in the liver

It is removed by the kidneys .


Removal of these wastes is important because their accumulation in the body is poisonous and can harm us. 

Parts of human excretory system :

The Human Excretory System - Teachoo.jpg

  • Kidneys: 

These are bean-shaped filtration organs , which remove urea, other waste salts and excess water from the blood in the form of urine (yellow liquid waste). 

  • Humans have 2 kidneys.
  • Each kidney is made up of a large number of excretory units called nephrons .
  • Nephrons have a cup shaped bowman's capsule at the upper end. The lower end of the nephron is a tubule.


Nephron = Bowman's capsule + Tubule


  • One end of the tubule is connected to the bowman’s capsule and the other to the urine collecting duct of the kidney.
  • Bowman's capsule has a number of small blood capillaries called glomerulus .
  • The glomerulus comes from the renal artery bringing blood containing waste and the other connects to the renal vein through the nephron tubule
  • The renal vein carries clean blood .
  • Ureters: 

These are two tubes which carry urine from each kidney , and open into the urinary bladder.

  • Urinary bladder: 

A stretchable bag which stores urine until the brain signals to release it.

  • Urethra: 

Urine is passed out from the body through the urethra .


Process of Excretion in Humans :

Nephron - Teachoo.jpg

  • The function of glomerulus is to filter the blood passing through it.
  • It lets substances like glucose, amino acids, salts, water and urea pass into the bowman's capsule and from there into the tubule .
  • In the tubule, all useful substances get reabsorbed whereas harmful substances (urea, unwanted salts, excess water ) remain in the tubule.
  • The tubule of the nephron then carries these wastes as urine into the collecting ducts of the kidney from where it is taken into the bladder via the ureters.
  • This waste is finally removed through the urethra .
Go Ad-free
Maninder Singh's photo - Co-founder, Teachoo

Made by

Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo