Circulatory System in Human

The human circulatory system is composed of the blood vascular and the lymphatic system.

Blood vascular system : In human beings it consists of blood, heart and blood vessels. It is responsible for various functions like transport, homeostasis and protection.

Blood Composition and Coagulation : Study of blood is called haematology. An average adult has about 4 to 6 litres of it — a red, slightly alkaline (pH about 7.4), salty, viscous fluid, heavier than water, classed as a fluid connective tissue because it develops from embryonic mesoderm. Its study is called haematology. Spun in a centrifuge, blood separates into two clearly different fractions: plasma, the straw-coloured liquid portion, making up about 55% of blood volume, and the formed elements — the blood cells — making up the remaining 44% (or so; the two fractions don't always sum to exactly 100% because a small remainder is buffy coat and rounding).

Plasma : Plasma itself is roughly 90% water, with the rest made up of dissolved substances: about 7-8% is protein (albumin, globulin, properdin, prothrombin, fibrinogen), about 1% is inorganic salts (sodium, potassium, magnesium, calcium, iron, manganese, chloride, bicarbonate and phosphate ions), and the remaining 1-2% is a mixed group covering digested food substances (glucose, amino acids, fatty acids, triglycerides), nitrogenous wastes bound for excretion (urea, uric acid, creatinine), regulatory molecules (hormones, enzymes, vitamins), the natural anticoagulant heparin, cholesterol and antibodies, and dissolved respiratory and other gases (oxygen, carbon dioxide, nitrogen).