The Basic Facts Blood is a living tissue composed of cellular elements and a watery fluid called plasma. Blood volume is the total amount of blood circulating within the body.
Blood has three main functions.
These are Transport, Defence against disease, and Regulation of body Temperature. Red blood cells are manufactured in the bone marrow of some bones including the Ribs, Vertebrae and some limb bones. RBCs, as they are called are produced at a very brisk pace of about 9000 million per hour. This is so because they have a short life of about four months. One reason for this is because they do not have a nucleus.