Between 7 and 8 percent of your body weight is blood, meaning that the average-sized man has about 12 pints of blood in his body, while an average-sized woman has approximately 9 pints. Whole blood is made up of two components: plasma and blood cells.
Plasma is a yellowish liquid made up of water, glucose, fat, vitamins, minerals, proteins and salt. By volume, it makes up just over one-half of whole blood, and is the transport system which moves blood cells throughout your body.
Red Blood Cells (erythrocytes) are your body’s energy carrier, transporting oxygen from the lungs to the rest of your body. These indented disks last only about 4 months before new ones are created to take their place.
Hematologists measure the volume of red blood cells in your blood (called the hematocrit), as it is an indicator of overall health. For instance, a low hematocrit reflects that you may be anemic due to blood loss, problems with your bone marrow, or nutritional problems, while a high hematocrit may reflect dehydration, certain types of diseases or even drug abuse.
White Blood Cells (leukocytes) make up approximately 1 percent of your blood, but are equally as important as their red counterparts, as they are part of the body’s defense system. Carried to the sites of infection, these short-lived cells begin to fight the infection in various ways. Some actually ingest bacteria or other foreign bodies, while others promote blood flow to damaged tissue. Physicians measure white blood cell counts, as it is one way that they can assess a patient’s health. Counts which are higher or lower than normal could signal infection, disease, tissue damage or allergies.
Platelets (thrombocytes) are not actually cells, but cell fragments formed in bone marrow. They help blood to clot at the site of a wound, and also release growth factors that help in the repair and regeneration of tissues. If the blood contains too many platelets, blood clots may form and block blood vessels, causing a stroke, heart attack or other incident. If there are too few platelets, excessive bleeding may occur.