Blood is a red opaque viscous liquid flowing in human blood vessels and heart. Blood consists of plasma and blood cells. One liter of plasma contains 900-9 10g of water, 65-85g of protein and 20g of low molecular weight substances. Low molecular weight substances contain many electrolytes and organic compounds. Blood cells include red blood cells, white blood cells and platelets. The average life span of red blood cells is 120 days, that of white blood cells is 9- 13 days, and that of platelets is 8-9 days.
Under normal circumstances, 40ml of blood cells die of aging every day. At the same time, there are a corresponding number of new cells. The function of blood includes two parts: blood cell function and plasma function. It has five functions: transporting, regulating human body temperature, defending, regulating human osmotic pressure and acid-base balance.
The main components are plasma, blood cells and genetic materials (chromosomes and genes). It is a special connective tissue, that is, the organizational level in the living system. Blood contains various nutrients, such as inorganic salts, oxygen, cell metabolites, hormones, enzymes, antibodies, etc., which have the functions of nourishing tissues, regulating organ activities and defending against harmful substances. Blood stores human health information, and many diseases need blood tests. Including genetic diseases.
The total amount of human blood is called blood volume, which is the sum of plasma and blood cells, but the number of other blood cells is very small except red blood cells, which is often ignored.