Blood and plasma (Appearance, composition and functions)


An average adult person has about 4-6 liters of blood, which forms about 8% of the body weight. The study of blood is called haematology (haema= blood, logos= study).


Physical appearance of blood:

  • Blood is opaque, mobile (moving or flowing) fluid connective tissue.
  • It is somewhat sticky and slightly heavier than water (specific gravity 1.06).
  • It is salty in taste and is mildly alkaline (pH 7.4).
  • Our blood is red in color when oxygenated (consisting of Oxygen) and purple when deoxygenated (consisting of Carbon dioxide).


Composition of blood:

  • Blood consists of a watery fluid called plasma which contains certain floating bodies collectively termed as formed elements.
  • Different kinds of blood cells like Erythrocytes (RBCs), Leukocytes (WBCs) and Thrombocytes (blood platelets) constitute up the formed elements.
  • Plasma (55%) and formed elements (45%) make up the total volume of blood.



  • Plasma is a faint yellow or straw colored, slightly alkaline viscous fluid.
  • It continuously takes up and loses materials as it flows through the capillaries, yet it has a constant chemical composition as given below:


S.N Components or materials Percentage (%)
1. Water 90%
2. Proteins:

(Albumen, Globulin, Fibrinogen, Prothrombin etc.)

3. Inorganic salts: (cations like Na, k, Mg, Ca, Fe and Mn) and

anions like chloride, bicarbonate and phosphate)

4. Others:

a) Food materials (glucose, amino acids, fatty acids, triglycerides etc.)

b) Waste materials (urea, uric acid, creatinine etc.)

c) Regulatory substances ( hormones, vitamins and enzymes)

d) Anticoagulants like Heparin

e) Cholesterol and antibodies

f) Dissolved gases (oxygen, carbon dioxide and nitrogen)



Functions of blood plasma

  1. Transport of food: Food materials such as glucose, amino acids, fatty acids, vitamins and mineral salts are carried by plasma from the alimentary canal and liver to all the tissues of the body for the growth , repair and energy.
  2. Transport of waste materials: Nitrogenous waste products like urea, uric acid and creatinine are carried from liver and other tissues to the kidneys for removal in the urine.
  3. Transport of hormones
  4. Transport of metabolic intermediates: Plasma carries metabolic intermediates like lactic acid formed in muscles during anaerobic respiration (in the absence of Oxygen) to the liver where it is partly oxidized and partly changed into glycogen.
  5. Regulation of water balance: Plasma regulates the water balance of the body, as it supplies water to the tissues and receives the excess water formed in metabolic processes.
  6. Regulation of pH: It helps regulate the pH of body fluids as it contains buffer materials such as proteins and mineral salts which can regulate the acids and bases entering the blood.
  7. Regulation of body temperature: Plasma carries heat from the heat producing tissues such as muscles and glands to other parts where no or little heat is produced or to the body surface where it can be distributed or dissipated.
  8. Moistening of tissues: Plasma keeps the tissues moist by leaking through the capillary walls as tissue fluid.
  9. Prevention of blood loss: Prothrombin and Fibrinogen proteins of plasma help in blood clotting or blood coagulation at the site of injury, which prevents the loss of blood.
  10. Immunity: Antibodies present in plasma provide immunity against certain diseases.

Blood and plasma (Appearance, composition and functions)