The document discusses the functions of blood and blood vessels in the human body. Blood transports oxygen, nutrients, waste materials, and hormones throughout the body via blood vessels. Tissues and cells rely on oxygen and nutrients from the bloodstream, producing carbon dioxide as a byproduct of cellular respiration. The thin walls of capillaries allow for exchange of molecules between blood plasma and surrounding tissues. Red blood cells transport oxygen and carbon dioxide while white blood cells are part of the immune system.
