There is actually a disease called Sickle Cell Anemia in which the red blood cells cannot carry oxygen well which causes the blood cells to curve like a crescent moon. Curved red blood cells cannot move easily and can become stuck in small blood vessels, blocking them. Once the blood vessel is blocked, blood cannot get to that part of the body. Organs then don´t receive normal blood flow which causes them to become damaged over time. This is a very serious disease and there currently is not known cure - we don´t know how to reshape red blood cells once they are damaged.