An adult human has about 4–6 liters of blood circulating
in the body. Among other things, blood transports oxygen to various
parts of the body.
Blood consists of several types of cells floating around in a
fluid called plasma.
The red blood cells contain hemoglobin, a protein that binds
oxygen. Red blood cells transport oxygen to, and remove carbon
dioxide from, the body tissues.
The white blood cells fight infection.
The platelets help the blood to clot, if you get a wound
The plasma contains salts and various kinds of proteins.