Blood is a complex mixture of
Plasma (the liquid component)
Red blood cells (the oxygen-carrying component)
White blood cells (the cells that defend against infection)
Platelets (particles that promote clotting)
The body contains about 5 to 6 quarts (about 5 liters) of blood.
Blood performs various essential functions as it circulates through the body:
Delivers oxygen and essential nutrients (such as fats, sugars, minerals, and vitamins) to the body's tissues
Carries carbon dioxide to the lungs
Carries waste products to the kidneys for elimination from the body
Transports hormones (chemical messengers) to allow various parts of the body to communicate with each other
Carries components that fight infection
Carries components that stop bleeding
Once blood is pumped out of the heart, it takes 20 to 30 seconds to make a complete trip through the circulation and return to the heart.
