Hii Friends, Today we are going to discuss about Composition of Blood.

Blood – Blood is a main circulating fuild in the human body. Study of blood is called Hematology. The system in which blood is circulated throughout the body is called circulating system.


  • The main circulating, bright red, slightly alkaline fuild in the human body .
  • Study of blood is called haematology.
  • Blood is a fuild connective tissue derived from mesoderm. It has pH about 7.4.
  • There are about 5 litters of blood in the body which is about 8 %of the total body weight.

Composition of blood


There are two main components of blood, viz.,

  • Plasma (55%)
  • Blood corpuscles (45%)


  • Plasma is a straw coloured fuild part of blood, slightly alkaline, viscous fuild consisting of 90 – 92 % water and 8-10% of solutes.
  • Solutes are 7% proteins (serum,albumin,serum globulin, heparin, fibrinogen and prothrombin).
  • Other solutes are nutrients (glucose, amino acids, fatty acids and glycerol.)
  • Nitrogenous wastes such as urea, uric acid, ammonia and creatinine.
  • Gases like oxygen, carbon dioxide and nitrogen.
  • Regulatory substance like enzymes and hormones.
  • Inorganic substances like bicarbonates ,chlorides, phosphates and sulphates of sodium potassium, calcium, magnesium, etc.

Blood corpuscles


Blood corpuscles are solid part of blood. They are of three types, viz. Erythrocytes (RBCs), leucocytes (WBCs) and thrombocytes (platalets) .

Erythrocytes or RBCs

  • Circular, bioconcave, enclueated cells of about 7micrometer in diameter and 2.5micrometer in thickness.
  • RBC count is about 5.1 to 5.8 million RBCs in male and 4.3 to 5.2 million in females. The average life span of RBC is about 120 days.
  • Erythropoiesis is formation of RBCs. It occurs in liver and spleen in foetus and in red bone marrow in adults.
  • The old RBCs are destroyed in liver and spleen.
  • Polycythemia is increase while erythrocytopenia is decreases in number of RBCs.
  • RBCs contain respiratory pigment called haemoglobin which helps in transport of oxygen and carbon dioxide.
  • The normal haemoglobin content in adult male is 13-18 mg/100 ml of blood and 11.5-16.5mg/100 ml of blood in adult female.
  • Less amount of haemoglobin leads to anaemia.

Leucocytes or WBCs

  • Leucocytes are colourless, nucleated, amoeboid and phagocytic cells.
  • They show diapedesis, I.e. squeezing out of blood capillaries by amoeboid movement.
  • The size is about 8 to 15 umicrometer.
  • Total WBC count is 5000 to 9000 WBCs /cu my of blood.
  • The average life span of WBCs is about 3 to 4 days.
  • Leucopoiesis or formation of WBCs. It occurs in red bone marrow, spleen, lymph nodes, tonsil thymus and payers patches.
  • Leukemia or blood cancer is a pathological increase in no of WBCs.
  • Leucocytes are of two types, viz., granulocytes and agranulocyctes.

Thrombocytes or platalets

  • Thrombocytes are smallest, nonnucleated, round and biconvex. They are of about 2.5 to 5 micro m in diameter.
  • Their life span is about 5 to 10 days.
  • Megakaryocytes of bone marrow from thrombocytes.
  • Thrombopoiesis is the formation of platelets.
  • Thrombocytosis is the increase while thrombocytopenia is the decrease in platalets count.
  • Thrombocytes help in coagulation of blood by releasing thromboplastine.

So guys, I hope you have understood the concept of composition of blood through this information. Share this information friends and family.

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