Blood is amazing stuff. Its main ingredient is water, which forms the plasma that carries cells and other substances in the blood. When you don't drink enough fluid, the volume of your blood drops and so your blood pressure drops. Your heart rate increases in an attempt to keep blood flowing to vital organs: your brain, heart and others. Eventually, you become lethargic, and extreme dehydration can lead to coma and death.

Besides water, blood is composed of three types of cells: red blood cells, white blood cells and platelets. Each of these has an important function.

Red blood cells carry oxygen from the lungs to all the tissues in the body. Without oxygen, you cannot survive.

White blood cells are an important part of your immune system. They help fight infections and allergies.

Platelets are necessary for blood to clot when you are injured. Without platelets, you could bleed to death from an injury.

Blood carries nutrients to all the cells of the body. Everything you eat, except for fiber, is broken down by digestion and ends up in your blood. Most of what you eat is broken down into glucose, which is used as fuel by the body. Vitamins, minerals and electrolytes (such as salt and potassium) are all carried by the blood to tissues where they are needed.

The thought of blood conjures up vivid images for most of us. It's quite common to fear the sight of blood, whether it is someone else's blood or your own. If the world were a less dangerous place, you would never have to think about blood, since it would stay inside of us, where it belongs.

Unfortunately, bleeding happens. Injuries and certain medical problems can cause internal and external bleeding. Some diseases and cancers - as well as some types of chemotherapy for cancer - can disrupt the body's ability to create the normal amount of new blood cells.

Blood transfusions - using another person's blood to quickly replace lost blood - have been common for only about the last 100 years. During the Civil War, doctors had no way of helping soldiers who were dying of blood loss. Now, every hospital in the country has access to a blood bank and can give blood transfusions to accident victims, surgery patients and those suffering from diseases that cause blood loss.

The Red Cross collects blood from donors and distributes it to hospitals all over the country. A unit of blood (about a pint) must be used within 42 days of donation, so new blood donors must constantly be found.

If you are 17 years or older, weigh more than 110 pounds, are in good health and without risk factors for hepatitis or HIV, you are probably eligible to donate blood. You can donate platelets or plasma every two days, but must wait 56 days between blood donations. Your body replenishes your blood supply quickly, and you won't even miss the blood that you give.

Donating blood is no more painful than having your blood drawn; it's a similar process but takes about 10 minutes. The entire blood donation experience takes about an hour. This includes filling out a questionnaire and an interview with a nurse to be sure you are eligible, blood pressure, pulse and temperature checks and an anemia check (done by pricking your finger and taking a drop of blood).

The Red Cross doesn't pay you to donate blood, but they do give you juice and cookies. Most people who donate blood regularly say that just knowing that they have helped save a life is reward enough.

Kathryn B. Brown is a family nurse practitioner with a master's degree in nursing from OHSU. Is there a health topic you would like to read about? Send your idea to


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