What is blood and its composition?

We are going to learn the queries What is blood and its composition? Blood is a fluid connective tissue which keeps circulating within blood vessels which is a system of closed tubes.

What is Blood and Composition of blood

Blood is a fluid connective tissue, which contains 55% plasma and 45% blood cells.

Blood is average 4.5 to 6 litres in volume in a healthy adult.

Blood is a composition of blood cells and Plasma.

There are three types of blood cells which are as follows

  • Red Blood Cells
  • White Blood Cells
  • Platelets

what is blood and its composition?


Plasma is a transparent, pale yellowish fluid which is non-living and contains several substances like hormones, antibodies, etc.

Also, plasma consists of 90% water and 10% of solids in the form of protein, fats minerals and carbohydrates.

It forms 55% of the total volume of blood in the human body.

Blood Corpuscles/Blood cells

Plasma contains scattered blood corpuscles.

They consist of Red Blood Corpuscles(RBC), White Blood Corpuscles(WBC) and Blood Platelets.

It is about 45% of the total volume of blood.

Red Blood Corpuscles or erythrocytes (RBC):

In the human, the RBCs are circular, biconcave and disc-shaped cells. They have no nuclei. Each cubic mm of circulating blood contains 45 to 50 lakhs of RBCs.

In adults, they are formed in bone marrow such as ribs, vertebrae etc. from here they escape into the general bloodstream.


The life span of RBC is short about 4 months (127 days). Liver spleen destroys RBCs

The RBCs are red in colour due to the presence of a most important pigment known as haemoglobin(Hb).

Haemoglobin contains iron due to which RBC carries oxygen.

Oxyhaemoglobin (HBO) is the haemoglobin with oxygen. It is scarlet in colour.

Anaemia is a  condition when the number of RBCs or their content haemoglobin decreases, it leads to disease. Sometimes due to the same reason, there is less amount of oxygen inside the body.

Another name for oxygen- carriers are erythrocytes. They carry oxygen from the lungs to the body tissues and help in respiration.

White Blood Corpuscles or leukocytes (WBC):

WBCs are colourless and irregular in shape. They have nuclei but no haemoglobin.

Leukocytes or wandering cells are other names for WBCs because they wander from blood vessels to another Part.

They may be of granular and non-granular type.

Granular WBCs have multilobed nuclei while nongranular WBCs have round nuclei.

Neutrophils, eosinophils, basophils are granular leucocytes while lymphocytes and monocytes are non-granular.

They are far less numerous than the RBCs.

Each cubic mm of blood contains about 6,000 to 10,000 white blood cells.

Bone marrow, lymph glands form WBCs.

Their life span is of about 15 days.

Likewise RBCs, Liver and Spleen destroy WBCs.

If the number of WBCs remains in a person’s body above normal, it is called Leukaemia, which is a blood cancer.

WBCs, help in the defence of the body by phagocytosis with the production of antibodies and by neutralizing the toxic substances, produced by the germs.

Neutrophils ingest and destroy bacteria, eosinophils increase and become active in the presence of certain infections and allergies and basophils secrete an anticoagulant.

Similarly, Lymphocytes and monocytes are associated with the immune system.

Lymphocytes produce antibodies and monocytes ingest non-bacterial foreign substances during infection.

Blood Platelets or thrombocytes

Blood Platelets or thrombocytes are small, colourless, rounded or oval cells.

They appear spindle-shaped or rod-shaped in profile.

They are produced in the bone marrow and after a few days of life, they die in the spleen.

There is no nucleus and the span is of about 2 to 3 days.

Each cubic mm of blood contains 2 to 4 lakhs platelets.

They play an important role in the arrest of bleeding and the healing of wounds.

Frequently Asked Questions FAQs
What is blood made up of?

Blood is made up of 55% plasma and 45% blood cells. Blood cells is made up of red blood cells RBCs, white blood cells WBCs, and platelets.

what are the 5 components of blood?

The major component of blood is plasma and blood cells. Blood Cells can be further divided into 3 which are red blood cells RBCs, white blood cells WBCs, and platelets.


What 4 things make up blood?

The 4 things that make up blood are plasma, red blood cells RBCs, white blood cells WBCs, and platelets.


What are the 7 types of blood cells?

Blood cells can be categorized into 7 types among which one type is a red blood cell, the second type is white blood cells which is further categorized into 5 types viz. Neutrophils, eosinophils, basophils, lymphocytes, monocytes and the seventh one is Blood platelets or thrombocytes.


what is the formula for blood?

There is no exact formula for blood though the constituent of blood is 55% plasma and 45% blood cells.



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