Blood volume. If you are tired and no blood is able to get to your body and you heart keeps going faster your heart is probably going to fail.
Things like weight, time spent drinking , gender .. etc.
Your stressing your self out, you will wont start to lose your muscle mass
bone marrow <span>contains hematopoietic stem cells, which give rise to the three classes of blood cells that are found in the circulation: white blood cells (leukocytes), red blood cells (erythrocytes), and platelets (thrombocytes)</span>