Blood isn't everyone's favorite topic. In fact, you'd probably feel a lot better if it just stayed inside your body where it belongs. But so many people either lose blood through surgery, injury, or because their bodies cannot manufacture blood components because of disease that blood transfusions are a life-saving measure. In fact, about 5 million people each year in the United States get blood transfusions.

A Bit About Blood
Blood is like the body's transportation system, always busy making deliveries and pickups. As blood circulates throughout the body, it delivers oxygen and nutrients to all the places they're needed. Blood also collects waste products, such as carbon dioxide, and carries them to the body's organs responsible for making sure the wastes leave the body.

Blood is made up of several main parts, and each has a specific job:

• Red blood cells carry oxygen to and remove carbon dioxide from all of the body's tissues.
• White blood cells are part of the immune system. Their job is to fight infection.
• Platelets are cell fragments that clot, which helps to prevent and control bleeding.
• Plasma is a yellowish liquid that contains substances that help clotting, along with other important blood components.

Blood is a mixture of these three types of blood cells and plasma. The blood cells are made in the bone marrow, a soft tissue contained within the bones. A full-grown adult has about 10 pints of blood in his or her body.

What Are Transfusions?
When blood or one of its components, such as red blood cells or platelets, is delivered into a person's bloodstream, it's called a blood transfusion. Transfusions are usually given through a tiny tube that is inserted into a vein with a small needle. The whole procedure usually takes about 1 to 3 hours, depending on how much blood is needed.

It's vital that the blood of a person receiving a transfusion is compatible with the donor's blood. Blood is classified into different types: A, B, AB, and O. You inherit your blood type from your parents. Blood types are also classified as either Rh positive or negative. You'll typically hear blood types described according to both of these characteristics - for example, "A positive" or "AB negative."

In emergencies, there are certain exceptions to the rule that the donor's blood type must match the recipient's exactly. Type O Rh-negative blood, which is called "O negative" or the "universal" blood type, is often given in emergencies because it's the only type that people with all other blood types can safely receive. O negative donors are called "universal donors." People who have type AB blood are called "universal recipients" because they can safely receive any type of blood.

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Jump to another section of this article Blood Transfusions Why Do People Need Transfusions? and Where Does the Blood Come From? Do People Get Sick From Transfusions? What Are the Risks of Donating Blood? and Who Can Donate Blood? Reviewer name and date on last page