Understanding Bleeding

What is blood?

Blood is a fluid that carries essential substances around the body through two types of blood vessels: arteries and veins. Arteries carry oxygenated blood away from the heart to the rest of the body. Veins then carry blood back to the heart and lungs to pick up more oxygen.

Blood is made up of water, proteins and other molecules and blood cells. There are three types of blood cells:

• Red blood cells — the main type of cell in blood — contain hemoglobin, a protein that picks up oxygen from the lungs and releases it throughout the body.
• White blood cells fight infections.
• Platelets help keep blood from leaking out of broken blood vessels by sealing the leak.

Blood also contains plasma, known as the liquid portion of blood. Plasma is 90% water and contains proteins and other molecules necessary for a variety of important functions, including blood coagulation.

How does blood clot?

Blood clotting, or coagulation, is the process that controls bleeding by changing blood from a liquid to a solid. Clotting is a complex process involving as many as 20 different plasma proteins, also known as blood clotting factors.

Within seconds of an injury, tiny cells in the blood, called platelets, bunch together around the wound. Blood proteins, platelets, calcium and other tissue factors react together to form fibrin, a substance that forms a blood clot, acting like a net over the wound. Over the next several days to weeks, the clot strengthens and then dissolves when the wound is healed. When certain coagulation factors are deficient or missing, however, the process doesn't occur normally.

What happens when you have a bleeding disorder?

In people with bleeding disorders, clotting factors are missing or don't work as they should. Generally, this causes them to bleed for a longer time than those whose clotting factor levels are normal. Bleeding problems can range from mild to severe.