Blood

As this site will be about a blood disease and living with it, a brief review of how our bodies create this essential item called blood is a good place to start. And it should be noted, I am not an expert, I have no formal training in this; everything here is distillation of all my readings once I developed a more serious interest in blood.

What exactly is blood?

Our blood teems with life. Billions of cells float about carrying oxygen, repairing leaks, and fighting bacteria. Millions of cells die every second and are replaced by new cells produced in the bone marrow and to a lesser extent in the spleen and the lymph glands.

Blood is made up of four main constituents: Plasma, Red Cells, White Cells and Platelets.

Plasma makes up about 55 percent of blood. It is 92 percent water and the other 8 percent is a host of substances indispensable to life. Among these are nutriments – glucose, fats and amino acids; the inorganic minerals such as potassium, calcium and sodium; an array of antibodies that help fight of viruses and other unwelcome intruders; and hormones such as insulin and adrenalin. Plasma maintains the body’s chemical balance, water content and temperature at a safe level, all the while helping to transport food, oxygen and waste.

Red blood cells outnumber white cells 700 to 1. The red cell is the carrier of oxygen, picking up the oxygen from the lungs and then carrying it to the rest of the body, and then bringing back the waste carbon dioxide. Red cells get their colour and ability to carry oxygen from their content of hemoglobin, a compound of protein and iron. Hemoglobin provides the red cell with a way of absorbing oxygen, carrying throughout the body.

White cells are the body’s defense force, coming into action whenever a foreign body enters our body. White cells are carried through the body in our blood, but have the amazing ability to leave the bloodstream to fight off invading bacteria and then return to the blood stream. White cells gather in great numbers at the site of an infection, the body can quickly manufacture more, often doubling the usual numbers within hours – this rising white count often serves as an early tip-off to dangerous infections.

Platelets are the most plentiful cells and the smallest cells in our blood. Platelets serve as the repair crew in our blood circulation system, responsible for the clotting action. When they touch the roughened surface of a torn blood vessel, they burst apart releasing chemicals that set off a chain reaction that convert a protein in the plasma into a mesh that snares red cells thereby forming the clot which seals the leak.

Where does blood come from?

Blood cells are produced in the bone marrow, a jellylike substance inside the bones that is composed of, among other things, fat, blood, and special cells that turn into the various kinds of blood cells. In children, the marrow of most of the bones produces blood. But in adults, only the marrow of certain bones — the spine, ribs, pelvis, and some others — continues to make blood. Bone marrow that actively produces blood cells is called red marrow, and bone marrow that no longer produces blood cells is called yellow marrow.

All blood cells come from the same kind of stem cell, which has the potential to turn into any kind of blood cell. These stem cells are called pluripotential (many potential) hematopoietic (blood producing) stem cells.

As the blood cells develop from the stem cells in the marrow, they seep into the blood that passes through the bones and on into the bloodstream. The different kinds of blood cells have different “life spans” — red blood cells last about 120 days in the bloodstream; platelets about 10 days; and the various kinds of white blood cells can last anywhere from days to years.

The body has a feedback system that tells it when to make new red blood cells. If bodily oxygen levels are low (as they would be if there are too few red blood cells circulating), the kidneys produce a hormone called erythropoietin (this would be the bicycle racer blood enhancer), which stimulates the stem cells in the marrow to produce more red blood cells.

Stem cells are capable of dividing and renewing themselves for long periods. Unlike blood cells—which do not normally replicate themselves—stem cells may replicate many times, or proliferate.