The blood is a liquid tissue composed of water, dissolved substances and blood cells. The blood circulates inside the blood vessels thanks to the impulse it receives from the contraction of the heart. A principle function of the blood is to distribute need to ends to all the cells of the body.
A. Red blood cells
These cells are Phantom cells, because all they contain is a large amount of haemoglobin, a protein that has a great affinity for combining with oxygen. The red blood cells, which circulate in the blood, bring oxygen to the cells that need it, and they also remove a small part of the carbon dioxide that the cells are discarding as waste. Because they cannot reproduce themselves, they must be replaced by new red blood cells that are produced by the bone marrow.
White blood cells or leukocytes
Leukocytes, or white blood cells swims in the blood plasma. They are called white because of their colour when viewed under microscope.
Platelets
These are cell fragments that have separated from the megakarocytes, cells located in the bone marrow. They have a role in blood coagulation. Next to the red blood cells, the platelets are the most abundant component of the blood.
Plasma
Red and white blood cells and platelets make up 45% of the blood. The remaining 55% is plasma, a fluid that is 90% water and the rest various nutrients.
The blood groups
Each person belong to a blood group. Within the ABO system, the groups are A,B,AB, and O. Each group is also identified with an antigen, or Rh factor, that is present in the red blood cells of 85% of the population. It is of vital importance to know what blood group a person belongs to so as to give only the right type during a blood transfusion. The immune system, via antibodies and antigens, will accept the body's own blood type but will reject the wrong type.
Individual with red blood cells with antigen A in its membrane belongs to blood group A, and that person's plasma has antibodies against type B. These antibodies recognize red blood cells with antigen B in their membrane as foreign.
People with this group have antigen B in the membrane of their RBCs and anti-A antibodies in their blood plasma.
Members of this group have antigen A and B in the membrane of their red blood cells and no antibodies in blood plasma.
Individual with this blood group have no antigens in the membrane of their erythrocytes and anti-A and anti-B antibodies in their blood plasma.
