The Composition and Function of Blood

  Blood is a body fluid in humans and animals that transport necessary substance such as nutrients and oxygen to the cells or tissues and remove metabolic waste products (carbon dioxide) away from those same cells.

Blood contains 7-8% volume of Body Weight.
  Females : 4-5 Litre
  Male : 5-6 Litre
  PH : 7.4

Functions of Blood:

Blood is technically considered a connective tissue, and as such it is the only fluid tissue in the body, full of fibrous proteins. The main functions of blood are -
  • Supply of oxygen lung to tissues (bound to haemoglobin, which is carried in red blood cells).
  • Removal of waste such as carbon dioxide, urea, and Uric acid.
  • Supply of nutrients such as glucose, amino acids, and fatty acids (dissolved in the blood or bound to plasma proteins).
  • Immunological functions, including circulation of white blood cells, and detection of foreign material by antibodies.
  • Coagulation, the response to a broken blood vessel, the conversion of blood from a liquid to a semisolid gel to stop bleeding.
  • Messenger functions, including the transport of hormones and the signalling of tissue damage.
  • Maintains body temperature, Acid-Base balance and balance of water level.

Composition of Blood Blood :

Blood is made up of 55% of Plasma (Non Cellular) and 45% of Cells (Cellular).

Plasma (55% of blood)
The composition of Plasma

  • 91% Water
  • 7% Proteins (Albumin, Fibrinogen, Globulin)
  • 2% Nutrients (sugar, Amino Acid, lipids,..)
  • Hormones (eg Insulin, T3,T4, TSH,etc.)
  • Electrolytes ( Sodium, Potassium, Chloride...)
  • Waste Product (Urea, Bilirubin, Creatinine,...)
  • Gases ( CO2, NO2, N2..)
  • lons & Minerals ( Ca , Mg, Fe, Zn,PO4, HCO3, H)

Cells (45% of blood)
The composition of Blood cells

  • 44% Red blood cells(RBC) & Platelets
  • 1% WBC (Neutrophil Basophiles Eosinophils Lymphocytes Monocytes).


  • Plasma is a sticky fluid made up of water. Plasma also containing a variety of proteins, nutrients, ions, gases and hormones.
  • The most abundant plasma protein is called albumin, which contributes significantly to plasma’s osmotic pressure. Globulin proteins are useful in transportation of nutrients.

RBC (Red Blood Cells) or Erythrocytes

  • RBC contains haemoglobin which is carry oxygen & nutrients and transport throughout of the body.
  • Shape of RBC is circular, biconcave non-nuclectic, disc shape.
  • Size : 7-8 micrometer & Thickness: 2 micrometer.
  • life Span of RBC is 120 Days.
  •  Amount of RBC in men is 4.7 to 6.1 million cells per microlitre (cells/mcL) and in women is 4.2 to 5.4 million cells/mcL.
  • RBCs formed in bone marrow.
  • RBC Destroyed in Spleen (it also called Grave of RBC).
  • Vitamin B12 & folic acid used to stimulate in RBC maturation.
  • Deficiency of any component of RBC promotes Anaemia.

White Blood Cells (WBC ) or Leukocytes

  • WBCs are Circular in shape, Smaller in Size, Nuclecti disc, Colour less.
  • All white blood cells have nucleus.
  • WBCs are Formed in bone marrow and destroy in blood.
  • Life Span of WBC is 5-7 Days.
  • Amount of WBCs in blood is 7-11 thousands cells per microlitre (cells/mcL).
  • lt Protects our body by harmful foreign particles or infectious diseases
  • lt enhance to stimulate Antibody Production.
  • WBC can be divided in two category on the basic present of Granules and Agranules.

Classification of WBC

  • Granulocyte WBC has Granules in their cytoplasm. E.g. Neutrophils 50-75%, Basophils 0-1%, Eosonophils 1-35%.
  • Agranulocytes has not any granules in their cytoplasm. E.g. Lymphocytes 7-15% and Monocytes 20-40%.

Platelets or Thrombocytes

  • •Platelets are very smaller in size 2-3 micrometer.
  • •It doesn't contains nucleus.
  • • The amount of platelets in blood is 150,000 to 450,000 platelets per microliter of blood. 
  • • Platelets Helps in blood clotting.
  • • Platelets flow through the bloodstream in an inactive state unless needed, dying every ten days and constantly regenerated.