How does a red blood cell know its function since it does not have a nucleus?
RBC are more like a machine then a cell with a nucleus. Their actions are dependant on hormones, receptors, blood composition, etc. They have a semipermable membrane like most cells that let things like carbon dioxide, hydrogen, oxygen, and bicarbonate ions in and out. They are sort of like a bus that carries substances where they need to go in the body. Their actions are controlled by the nervous systems. When blood composition moves away from homeostaisis receptors (chemoreceptors, barorecptors, etc) are stimulated sending action potential to the brain (usually through the vagus, cranial, and glossopharygenal nerves). The specific part of the brain stimulated then releases hormones to move the blood back to homeostaisis (for example the adrendal medulla might release epnipherine).
