Excretory System Study Guide

Investigate the excretory system, identify its 5 major constituent organs, and learn about their structures and functions within the human body.


Excretion is the body’s process through which waste materials are removed. The body metabolizes the food that we consume for various processes. After the breakdown of fats, proteins, sugars, and other nutrients, the cells send the waste products for removal.

The excretory system then removes the metabolic waste through various components, including the kidneys, liver, lungs, and skin. For the scope of this article, the focus is on the excretory system in human; the kidneys and the urinary system are emphasized.

What is Excretion?

Excretion is the biological process of removing excess waste and water from the body. By removing the metabolic waste, the excretory system in human beings maintains homeostasis. While kidneys form the major part of the excretory system, several other organs are also involved in excretory activity, such as the liver, skin, large intestine, and lungs.

What are the Functions of the Excretory System?

The excretory system removes solid, liquid, and gaseous waste in the way as summarized below:

  • The water vapor and carbon dioxide waste are exhaled through the lungs.
  • The liver breaks down several toxic substances present in the blood, along with excess amino acids.
  • The skin also acts as the excretory system in humans by removing excess salts and water.
  • The kidneys filter out the blood and remove most of the metabolic waste produced in the body, including hormones and ionic salts.
  • The large intestine eliminates the waste products left over after digestion.

What are the Parts of the Human Excretory System?

The excretory system parts consist of these four main units:

  • A pair of kidneys
  • A pair of ureters
  • A urinary bladder
  • A urethra


  • Kidneys are the main organs of the excretory system in human beings where filtration, selective reabsorption, and urine production occurs.
  • They are dark, bean-shaped organs that measure 10cm long and 6cm wide.
  • The kidneys contain nephrons which perform the filtration of blood within the organ.


The ureters are tube-like structures that carry urine from the kidneys to the urinary bladder. The ureters connect the kidneys to the urinary bladder.

Urinary Bladder

The urinary bladder is a muscular sac-like structure that can expand and contract to accommodate urine. The opening of the urinary bladder is controlled by a muscular sphincter that opens during urination.


The urethra is a short, muscular tube through which the urine is expelled out.


  • The human excretory system comprises the kidneys, ureters, urinary bladder, and urethra.
  • It removes the waste products of cellular metabolism, maintains salt-water balance, and filters out toxins from the body.


1. What is the excretory system and its function?

The excretory system of the body performs the task of excreting the waste produced after cellular metabolic processes.

2. What are the four excretory systems?

The excretory system in human beings includes the organs such as kidneys, lungs, liver, and skin.

3. Where is the excretory system in the body?

The main excretory system, which is the urinary system, is located in the lower abdomen.

4. What are the parts of the excretory system?

The main parts of the excretory system are the kidneys, ureters, urinary bladder, and urethra.

5. What are the three main functions of the excretory system?

The three main functions of the excretory are filtration, reabsorption, and production of urine.

6. What are the 7 functions of the kidney?

The 7 main functions of the kidney are:

  1. Controlling water balance
  2. Maintaining electrolyte balance
  3. Maintaining acid-base balance
  4. Removing waste products and toxins from the body
  5. Controlling blood pressure
  6. Secreting the hormone erythropoietin
  7. Vitamin D activation

7. What are some examples of the excretory system?

Some of the examples of the excretory system include:

  • Filtration of blood by the urinary system
  • Exhalation of carbon dioxide from lungs
  • Elimination of salt and fluids through the skin

8. What are the functions of the nephron?

The nephron is the basic unit of the kidney which regulates the solutes in the blood. It filters the blood and selectively reabsorbs what is necessary, and discards the rest as urine.

9. What is the importance of the excretory system?

The excretory system maintains homeostasis by regulating water and electrolyte balance and eliminating metabolic waste.

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