Blood is a connective tissue and is the liquid medium through which transportation of materials is brought about.
In a living being the blood is constantly circulated from the heart to the arteries and back through the veins. In an adult human 5 to 6 litres of blood is present in the body and it makes upto 7-8% of the body weight.
The blood is saltish to taste and is slightly alkaline with a pH of 7.3 to 7.45. The blood when taken from an artery is bright red in colour. It is dark red in colour when taken from a vein.
The study of blood is called haematology.
Blood always moves from the heart through the arteries and back to the heart through veins.
Composition of Blood
Plasma
Plasma is pale yellow, clear, slightly alkaline (pH, 7.4) and viscous fluid component of blood.
Plasma derived from Greek word ‘ plasma’ which means something moulded.
It forms 55-60 percent of blood volume, plasma contains, 92% liquid and 8% solids
Water 80 - 82 %
Inorganic salts 1 - 2 %
Organic components 7 - 10 %
It also contains several salts, glucose, proteins, amino acids, fats, enzymes, hormones, antibodies and also digested and excretory products of food.
Blood is buffered effectively by protein and salts by which the approximately pH is about 7.4. They also maintain the osmotic pressure of blood so that the water has an automatic tendency to enter the blood capillaries.
Anticoagulants
They are of two types, antithrombin and heparin. Antithrombins prevent blood coagulation inside blood vessels by inactivating or neutralising thrombin formed in blood. Heparin enhances the activity of antithrombin.
Inorganic salts in plasma chlorides, carbonates bicarbonates sulphates and phosphates of sodium, potassium, calcium, magnesium, iron etc.
Lysozyme is proteinaceous enzyme that is antibacterial and it causes breakdown of bacterial walls.
Serum is blood plasma from which fibrinogen, the blood clotting protein, has been removed. It is a yellow-coloured fluid.
There are many types of organic compounds in the blood.
Plasma proteins mainly albumin (4 %), globulin (2.5 %) and fibrinogen (0.3 %).
Prothrombin : It is a type of -globulin which is synthesized by liver. Prothrombin is changed to thrombin during coagulation of blood.
Fibrinogen : It is globulin type of protein which is cleaved and changed into fibrin during coagulation of blood.
Nutrients dissolved in plasma are glucose, amino acids, fatty acids and vitamins.
Excretory substances like urea, uric acid and creatinine.
