Blood: Definition, Composition, Types & Functions

Blood is a fluid connective tissue that consists of plasma, blood cells and platelets.

What is blood

Blood is a body fluid in the circulatory system that providing the body with nutrition, oxygen, and waste removal. It also transport metabolic waste products away from those same cells.

Your blood is made up of liquid and solid parts. The liquid part is plasma it is made up of water, salt, and protein. The solid part of your blood contains red blood cells (RBCs), white blood cells(WBCs), and platelets. Red blood cells (RBCs) deliver oxygen from your lungs to tissue and organs.

Red blood cells (RBCs) deliver oxygen from your lungs to your tissues and organs. White blood cell (WBCs) fight infection and a part of your immune system. Platelets help blood to clot when you have a cut or wound.


Study of Blood

Study of blood is know as Hematology

Formation Of Blood

Process of blood formation is know as Haemopoiesis (in bone marrow).

  • Colour – Red
  • pH – 7.4(Slightly alkaline)
  • By weight – 7 to 8% of body weight
  • By volume – 5-6 liters in male and 4-5 liters in female
  • Blood is a false connective tissue because

a. Cells of blood have no power of division.

b. Fibers are completely absent in blood.

c. Matrix of blood is produced & synthesized by liver and lymphoid organs.

Types Of Blood Cells

There are three kinds of blood are – red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Red Blood Cells (RBCs)

It is also called erythrocytes. RBCs are biconcave cells without nucleus. They contain hemoglobin, a protein that gives blood its red colour and enable it to carry oxygen from the lungs and deliver it to all body tissues.

The normal shape of RBCs are biconcave cells without nucleus in human. RBCs are formed in the red bone marrow of bones. Stem cells in the red bone marrow are called hemocytoblast. The main function is to transport oxygen from our lungs to the rest of our body. They make the return trip, taking carbon dioxide back to our lungs to be exhaled.

White blood cells (WBCs)

WBCs (White blood corpuscles) are also called as leucocytes. They are colourless due to the leak of haemoglobin. White blood cells help your body fight infection.

The main types of white blood cell are:

  • Granulocytes- Eosinophils, Basophils, and Neutrophils
  • Agranulocytes- Monocytes and Lymphocytes


It is also called thrombocytes. They are tiny blood cell that help your body from clots to stop bleeding. Platelets are nonnucleated and derived from Megakaryocytes cells of bone marrow. They are biconvex disc like, oval shaped structure.

It help regulate blood flow when any part of the body is damaged, there by aiding in fast recovery through clotting of blood.

Composition Of Blood

Liquid part – Matrix – Plasma – 55% .

Solid part – Blood corpuscles – 45% (RBCs, WBCs & Platelets).

Components Of Blood

Basically four main components of blood- Plasma, Red blood cells, White blood cells, and Platelets.


Matrix of blood is called plasma. It is a biggest part of your blood. About 55% of the body’s total blood volume. It is pale yellow in colour due to urobilinogen (Bilirubin). It consists of salts, nutrients, water and enzymes. It is also contains important proteins and other components important for overall health.

Plasma contains 90% to 92% of water and 8% to 10% of solids. In which inorganic and organic components are present.

Red Blood Cells

Red blood cells contain a protein called haemoglobin, which carry oxygen from the lungs to all parts of the body. Red blood cells also remove carbon dioxide from your body. Red blood cell are made the bone marrow. The mature human red blood cell in small, round, and biconcave.

White Blood Cells

It is a part of the body’s immune system. They help the body fight infection and (such as bacteria, viruses, and fungi) and other disease that inter in your body. They protect you against illness and disease. White blood cell are made in the bone marrow.


It is a tiny blood cells that help from blood clots to slow or stop bleeding and to help wounds heal. Platelets are your body’s natural bandage to stop bleeding. Having too many or too few platelets or having platelets that don’t work as they should can cause problems.

Blood Vessels

In closed type of blood vascular system which carry blood to and form all parts of the body.

Types Of Blood Vessels

There are three types of blood vessels are:

  • Arteries
  • Veins
  • Capillaries


Arteries carry oxygen-rich blood away from your heart to all the tissues of the body It is strong tube and muscular in tube. Arteries is a part of your circulatory system. The aorta is the largest artery in the body.


Veins carry deoxygenated blood from all parts of the blood the heart. Veins are elastic blood vessels. veins are part of your circulatory system. The work together with other blood vessels and your heart to keep your blood moving.


Capillaries are tiny blood vessels have thin walls. It is bring about the exchange of substances between blood and tissues. They transport blood, nutrients and oxygen to cell in your organs and body systems.

Function Of Blood

Blood has many different function including:

Transport of Oxygen to the cell

The blood transports oxygen from the lungs to the cells of the body. And the west carbon dioxide move from the blood to the lungs and is breathed out.

Transport of hormones and nutrients

Endocrine glands release hormones into the bloodstream to the transported to various organs and tissues.

The wall of small intestine absorb glucose, minerals, vitamins, and protein are into bloodstream.

Helps maintain homeostatis

Blood helps to maintain to inward body temperature by absorbing or releasing heat.

Blood clotting

Platelets play a major role in blood clotting. Your platelets will clot to plug the hole in the blood vessel and stop the bleeding.

Blood Group

Antigen of blood group is present on the surface of RBC also called as agglutinogen. Antibody for blood group antigen is present in serum (Plasma) called agglutinin. Your blood group is determined by the genes your inherit from your parents. There are four main blood groups – A, B, AB, and O.

Each group can be either Rh positive or Rh negative, which means in total there are 8 blood groups.

Blood group O is universal donar & Blood group is AB is universal acceptor.

Who discover blood group

Landsteiner discovered the ABO blood group system by mixing the red cells and serum of each of his staff. He explained in 1901 that people have different type of blood cell, that is, there are different blood group.

ABO blood group

Blood grouping is of two antigens- Antigen and Antigen B The ABO grouping system is classified into four types based on the presence or nonappearance of antigen on the red blood cells surface and plasma antibodies.

  • Group A – Contains antigen A on RBCs and antibody B in plasma.
  • Group B – Contains antigen on RBCs B and antibody in plasma A.
  • Group AB – Contain both A and B antigen on RBCs and no antibodies (neither A nor B).
  • Group O – Contain neither A not B antigen and both antibodies A and B in plasma.

Rh Factor

The Rh factor was discovered by Landsteiner & wiener in 1940. The blood discover this blood type in Rhesus monkeys.

Rh factor is a protein found on the surface of red blood cells. If antigen is present then Rh positive. If antigen s absent then Rh negative.

In India % ratio of Rh is-

Rh positive – 97%

Rh negative – 3%

In world-

Rh positive – 80%

Rh negative – 20%

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