Science Study Notes on Human Excretory System

By Neha Joshi|Updated : March 4th, 2020

This article comprises detailed study notes on the topic of the excretory system. Questions on this topic are generally asked in the REETUPTETCTET and other teaching examinations. 

The excretory system is a process by which an organism gets rid of waste products from its metabolism. The three terms excretion, secretion, and egestion all describe the passing out of substances from organisms or cells. Removal of nitrogenous substances like urea, ammonia, uric acid, etc. formed during metabolism from the body of the human is called excretion.



Various animals and their excretory organs


Excretory organs

Unicellular animals



Direct by cells


Flame cells


Renette cells




Canal system

The main excretory organs of humans are as follows –

(i) Kidneys: kidneys are the most vital and prominent organ in the excretory system. The excretory process is mostly done by the kidneys.

  • In the human being, there exists a pair of kidneys which is dark-red, and bean-shaped.
  • Its weight is 140 grams.
  • There are two parts to it. The outer part is called the cortex and the inner part is called the medulla.
  • A kidney has about ten lakh structural and functional units, called nephrons.
  • Bowman's capsule is a cup-like structure in every nephron called.
  • The glomerulus of thin blood vessels is found in the Bowman's capsule which is made up of two types of arterioles.

(a) Afferent arteriole: An afferent arteriole connects the renal artery to the glomerular capillary network in the kidney's nephron, Which carries the blood to the glomerulus, starting the filtering process.

(b) Efferent arteriole: it has less diameter than afferent arteriole and takes blood out of the glomerulus.

Functions of the kidney:

  • It maintains the PH of blood.
  • Ultrafiltration – It is the process of filtration of liquids into the cavity of Bowman's capsule.
  • It maintains the salt contents of the body.
  • It eliminates toxic substances from the body.
  • Homeostasis – kidney removes various unwanted materials from the blood, it helps in keeping the internal environment of the body constant.
  • Kidney secrets an enzyme Renin which changes the plasma protein, the angiotensinogen.

(ii) Skin: The oil gland and sweat glands secrete sebum and sweat respectively. Along with sebum and sweat, some other excretory substances enhance the excretory process.

(iii) Liver: the cells of the liver transform the excessive amino acids and ammonia of the blood into urea which is the main excretory substance. And spleen split the damaged blood cells and separates them from the blood flow.

(iv) Lungs: in general Lungs are associated with the respiratory system but it also plays an important role in the excretory system. Lungs do the excretion of the gaseous substance. CO2 and water vapours and some substances like garlic, onion, and some species are also excreted by the lungs.

Different excretory Products

The list of various excretory products is as follows-

  • Nitrogenous waste material
  • Mineral Salts
  • Co2
  • Water
  • Pigments
  • Creatine and creatinine
  • Vitamins and Hormones 




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