Select Board & Class


Transportation in Animals and Plants

Body Fluids and their Function

Excretion and Its Importance

Excretory system consists of groups of organs that are responsible for excreting waste materials such as, harmful chemicals and other impurities from the body. The major excretory organ is kidney. However, there are some other organs also that perform the function of excretion.

Let us understand the function of the following organs as excretory organs.


Respiration is a necessary process that provides energy for cellular activities. During respiration, carbon dioxide gets accumulated in the cells, from where it diffuses into the bloodstream and is finally transported to the lungs. From lungs, this carbon dioxide leaves the body every time we exhale.






Liver helps in the excretion of various unneeded substances in the body. It converts toxic ammonia into urea, a harmless fluid, by the process of deamination. This urea is then filtered by the kidney into urine. It does not directly eliminate excretory substances.




Skin also acts as an excretory organ. It possesses glands, namely, sweat glands and sebaceous glands. Sweat is a watery fluid that consists of metabolic wastes like water, sodium chloride, lactic acid, amino acids, urea, glucose, etc.  Besides excreting metabolic wastes from the body, sweat also has a cooling effect on the body. On the other hand, sebaceous glands help in excretion of sebum which consists of lipids, fatty acids, etc.



How the other kinds of waste materials removed from the body? Is there a particular organ system that functions to remove waste materials from the body?

The organ system that performs the function of excretion is known as the excretory system. The excretory system removes the waste materials present in the blood.

Which organs are involved in this process? What mechanism is required for filtering blood?

The primary components of the excretory system are the kidneys, the ureter, the urinary bladder, and the urethra.

When blood reaches the kidneys, useful substances are absorbed back into blood, while the waste materials are dissolved in water and removed from the body in the form of urine.

The urine enters a long tube-like structure called the ureter. The ureter then passes the urine into the urinary bladder, which stores it until it is passed out of the body. Urine is passed out of the body through a muscular tube-like structure called the urethra.

Waste materials are also removed from the body through sweat. During sweating, water and salts are removed from the body.

What is blood and what are its functions?

Blood is a fluid connective tissue that flows in blood vessels. Its main function is to transport substances such as digested food and oxygen (from the small intestine and lungs respectively) to all parts of the body. It also takes part in the removal of waste materials from the body. How does blood perform all these functions? Does it have some special components that perform these functions? Blood is made up of various types of cells that are suspended in a fluid part called plasma. Plasma is a yellowish colour fluid, made up of water (~90%) and some dissolved nutrients, proteins, hormones and waste products. Let us study the various components of blood.

Blood consists of three types of cells. These are as follows.

  • Red Blood Cells or Erythrocytes - They contain a red pigment called haemoglobin, which transports oxygen to all cells of the body by combining with oxygen to form a compound called oxyhaemoglobin. The mature erythrocytes do not have a nucleus.

  • White Blood Cells or Leukocytes - They are larger than RBCs and do not have haemoglobin. They fight against germs that enter the body. Thus, they protect the body from diseases.

  • Blood Platelets or Thrombocytes - You must have noticed that when you get injured, bleeding stops after some time. This happens because of the activity of platelets. Platelets help in the clotting of blood during an injury. The platelets are smaller than the RBCs.

Some interesting facts:

  • After blood donation, the fluid gets replaced in few hours and the red blood cells within four weeks. It takes around eight weeks to restore the iron lost after donation.
  • Platelets are produced at the rate of 200 billion per day in the human body.

Functions of blood:

  • It transports nutrients and oxygen to the different parts of the body

  • It also carries waste materials (from the different parts of the body) to be removed by the excretory organs.

  • Chemical messengers like hormones are transported by the blood.

  • Protects the body from disease carrying germs.

  • Helps to maintain a constant body temperature.

Blood Clotting

  • Clotting is an important character of blood, which helps in preventing blood loss at the time of any physical injury.
  • The blood clot is formed with the help of platelets.
  • When any physical injury damages a blood vessel, the platelets release an enzyme that help in production of a protein, thrombin.
  • Thrombin protein converts fibrinogen protein present in the blood into fibrin.
  • These fibrin proteins form a fine mesh work around the…

To view the complete topic, please

What are you looking for?