Blood Type

Blood is composed of cells suspended in a liquid-like substance called plasma.

Suspended in the plasma are three types of cells:

- Red blood cells carry oxygen

- White blood cells fight infection
- Platelets stop bleeding in injuries

A blood type (also called a blood group) is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, glycoproteins or glycolipids, depending on the blood group system. Some of these antigens are also present on the surface of other types of cells of various tissues. Several of these red blood cell surface antigens can stem from one allele (or very closely linked genes) and collectively form a blood group system. 

Blood types are inherited and represent contributions from both parents. A total of 33 human blood group systems are now recognized by the International Society of Blood Transfusion (ISBT). The two most important ones are ABO and the RhD antigen, they determine someone's blood type (A, B, AB and O, with +, − or Null denoting RhD status).

The most common type of grouping is the ABO (either uppercase or lowercase) grouping. 

The varieties of glycoprotein coating on red blood cells divides blood into four groups: 

- A (A oligosaccharide is present) 

- B (B oligosaccharide is present) 

- AB (A and B oligosaccharides are present) 

- O (neither A nor B, only their precursor H oligosaccharide present) 

Blood transfusion is generally the process of receiving blood products into one's circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used whole blood, but modern medical practice commonly uses only components of the blood, such as red blood cells, white blood cells, plasma, clotting factors and platelets.

Please share, this might be very useful in case of emergency

Source: Wikipedia