Your blood cells are made in your bone marrow.
Marrow is the spongy part in the middle of the bone.
These special cells are called Stem Cells. Your ribs, skull, vertebrae, and some of your long bones make blood. Every second, more than 2 million red cells squeeze out of your bones through tiny tubes called capillaries. Over your lifetime, your bones will produce more about half a ton of blood cells. After a lifespan of about 120 days, old red blood cells are replaced by new ones.