Plasma is pale coloured, slightly alkaline clear, transparent, non - living fluid. It constitute about 55 - 60% of the blood. Plasma contains following components: Water: 90 - 92% Inorganic substances: 1% Plasma proteins: 6 - 8% Other organic substances: 1% Chlorides, carbonates, bicarbonates, sulphates and phosphates of sodium, potassium, calcium and magnesium are main inorganic substances found in plasma. Among organic substances plasma proteins like albumins, globulins, fibrinogens and prothrombin constitute about 6 - 8% part of plasma. All these proteins are soluble and present in colloidal form in plasma. Therefore, these make plasma viscous and regulate osmotic pressure. Prothrombin and fibrinogen proteins helps in coagulation of blood and forms 4% of plasma proteins. Albumin forms 50% of all plasma proteins and these maintain osmotic pressure of the blood. Globulins form 43% of total plasma proteins. These are of three types: ? - globulins, � - globulins and ? - globulins. ? and � globulins transport proteins to different parts of the body, while ? - globulins protect the body from infections. Plasma also contains ions such as Na+, Ca++, Mg++, HCO3- , Cl- etc. Plasma also contain glucose, amino acids and lipids due to any infection in the body. The blood clotting factors also present in plasma in inactive state. Plasma without clotting factor is called serum. 1. Plasma Proteins: These constitute about 70% part of plasma. These are of following type: Globulins or Immunoglobulins: These proteins form about 43% part of total plasma proteins. These are of three types: Alpha (?), Beta (�) Gamma (?) globulins. Alpha and beta globulins transport proteins to different parts of the body while gamma globulins protects the body from infections. Albumins: These proteins form about 53% of all plasma proteins. These maintain osmotic pressure of the blood. Fibrinogen and prothrombin: These form about 4% of plasma proteins. These help in coagulation of blood. 2. Organic and Digested Materials: Plasma contains carbohydrates (glucose, fructose, lactose), fats, fatty acids, amino acids, glycerol, vitamins, cholesterol, phospholipids, etc., in digested or undigested form. Plasma contain 80 - 100 mg glucose/100 mL blood and 0. 2% fat. Cholesterol is present about 50 - 180 mg/100 mL blood. 3. Salts: These are chlorides, carbonates, bicarbonates, sulphates and phosphates of sodium, potassium and iron. These form 0.9 - 1% part of plasma. Due to presence of them plasma is slightly alkaline (pH 7.3 - 7.5). Main cations are Na+ and anions are Cl-. 4. Excretory Substances: Urea, uric acid, ammonia (NH3), amino acids, creatinine etc., being dissolved in plasma. These are main excretory substances. 5. Hormones: Some hormones secreted by endocrine glands are being dissolved in plasma. Hormones are carry by the blood to their targets. 6. Enzymes: Plasma contains lipase, distase, glucolase, protease, esterase, nuclease, oxidase etc., enzyme. 7. Heparin: It is an anticoagulent, which checks blood clotting in blood vessels. It produced in basophils. The mast cells of liver also secrete heparin. 8. Antigen and Antibodies: Bacteria and external proteins reaching in blood are called antigens. Plasma produces special type of proteins to reduce the effect of these antigens. These proteins are called antibodies. They are inactive antigens. 9. Gases: The gases such as carbon dioxide, oxygen, nitrogen etc., are also dissolved in plasma. 10. Drugs: The drugs taken by the person also present in plasma. Functions of Plasma: 1. Plasma transports various nutrients, hormones, enzymes and excretory substances from one place to another. 2. Maintains fluid quantity of blood. 3. Heparin present in plasma do not allow to coagulate blood in vessels. 4. Its fibrinogen protein forms blood clot after injury. 5. The globulin protein acts as immunity. 6. It maintains pH of blood. 7. It regulates body temperature. 8. It removes excretory substances along with CO2 from body.