Blood is the vital liquid that circulates through the body. It is pumped by
the heart through the arteries, veins, and capillaries. It carries nourishment,
oxygen, heat, antibodies, hormones, vitamins, and electrolytes to every cell.
It carries away from those same cells carbon dioxide (CO2) and other waste
products to be disposed of via organs such as the lungs, liver, and kidney. Whole
blood contains red blood cells, white blood cells, platelets, and plasma.
Red Blood Cells (RBCs)
Red blood cells, also called erythrocytes, contain a complex
iron-containing protein called hemoglobin that gives blood its red
color. In every two to three drops of blood there are around one billion red
blood cells with an average life span of about 120 days. When there aren’t
enough red blood cells in the system, the kidneys release erythropoietin,
a hormone that alerts the bone marrow to make more. The average adult male has
a hematocrit (percentage of blood volume composed of red blood cells) of
about 47%.
White Blood Cells
White blood cells (WBCs) make up the body’s immune system and protect
it from bacteria, viruses, and fungus. In the marrow, white blood cells
outnumber the red by 2-1, but in the bloodstream the red blood cells outnumber
the white by 600-1. There are five types of white blood cells; neutrophils,
monocytes, lymphocytes, eosiniphils, and basophils.
Platelets
Platelets come from special cells called megakaryoctyes. They are the
smallest of the blood cells and make up 5%-7% of the blood volume. Platelets
have a life span of 9-10 days and are then (like the red blood cells) removed
from the body by the spleen. The platelets main function is to form clots to
stop bleeding.
Plasma
Plasma is the liquid portion of blood; a straw-colored, protein-salt
solution that is 90% water. The other 10% is composed of inorganic
electrolytes and blood proteins such as albumins, globulins,
fibrinogens, and hemoglobin. They all contribute to the multiple functions
that plasma performs, including maintaining blood pressure and supplying
blood-clotting proteins; it is also the transport and storage for important
minerals like potassium and sodium.
In order to preserve clotting factors, donated plasma is frozen within hours
of donation and can be stored for 1-7 years. It is often used to treat bleeding
disorders and used in a plasma replacement process called plasma exchange.
Plasma is the most frequently paid-for component of blood and can be collected
from a healthy donor up to two times a week.