Transport of nutrients, oxygen and water to each cell and the removal of the waste products from the body is called “circulation”

Circulatory System

Circulation, distribution and exchange of the useful and waste products in the body is carried out by some special organs. All this special organs together form the circulatory system. Circulatory system is of two types:

  • Open circulatory system
  • Closed circulatory system

Open circulatory system: It describes a system in which blood does not confined to the blood vessels instead blood flows freely in the open spaces of the body cavity. In it blood and interstitial fluid are allowed to mix in an organism. Interstitial  is just the fluid found between cells in the body.

Closed circulatory system: It is a system in which blood always flows in a closed vessels. So that blood will not mix with interstitial fluid.

Blood Vessels

The blood vessels are the system of channels in our body through which blood flows. Blood vessels are of the following types:

1)Arteries: Blood vessels which carry oxygenated blood  away from the heart to different parts of the body are known as arteries
2)Veins: Blood vessels which return the deoxygenated blood from various parts of the body to heart are known as veins.
3)Capillaries: Arteries and veins after entering into different organs in the body are divided into fine branches. This thin fine branches are called as capillaries. It acts as a connector between arteries and veins.


Blood is the main circulating medium in the body of man. It is soft, fluid, connective tissue. Blood is red, salty in taste and specific gravity is 1.05 to 1.06, and pH range from 7.3-7.5. Blood has two main components which are as follows:

A) Blood Plasma: It is 55% of the total volume of the blood. Its color is light yellow ans slightly alkaline in nature and composed of 90-92% water, 7-8% protein, 0.9% inorganic components, 0.1% glucose etc.

B) Blood Corpuscles: It is 45% of the total blood volume. It is following two types-

  • Red blood corpuscle or Erythrocytes.
  • White blood corpuscle or Leucocytes.

Erythrocytes or Red blood corpuscle: It contains hemoglobin pigment, due to which the color of the blood becomes red. It transports oxygen and carbon-dioxide.

Leucocytes or White blood corpuscle: Leucocytes are colorless, because hemoglobin is not present in them. It protect us from external invaders.

Function Of Blood:

1- Blood transports food, oxygen, carbon-dioxide, waste products.

2- It maintains the balance of water and regulate the temperature.

3- Control the blood loss by clotting.

4- Maintains the chemical coordination