The Basics of Blood
Most people discover blood at an early age, when they skin a knee or cut a lip. Just what is blood made of, and what does it do in your body?
Adults have about 6 liters of blood in their bodies, circulating through their arteries (going away from the heart) down into smaller and smaller capillaries, and then returning back to the heart in veins. They pass through the lungs in order to pick up fresh oxygen, and the heart pumps it around in circles.
It was only in 1616 that this "closed circuit" of blood was discovered by William Harvey in England.
The main 'liquid' of blood is called the plasma. The plasma contains 3 main types of cells. The red blood cells are the main part of the blood, carrying oxygen in to the cells and carbon dioxide back out of the cells. The white blood cells fight infection. The platelets sense trouble and form clots if you get a cut or scrape, to keep the rest of the blood from escaping.
There are over 300 different "types" of blood. The four main types are A, B, AB and O were discovered in 1909. If you are blood type A, it means you have an A "antigen layer" on the outside of your red blood cells. Your blood cannot be put into a person who is blood type B - because that B person's body would see your A antigen layer and think it meant your blood cell was something evil and dangerous.
Before 1909, people would often die from what was then called "blood poisoning" when they were given the wrong type of blood during an operation. Once blood types were discovered, these problems were solved.
More about Blood Types
Blood Types, Inheritance and Paternity
Blood Type Distributions Around the World
Blood Types and Transfusions
Blood Types and Illnesses
Important Types of Blood
Evolution of Blood Types
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