Inside your bones is a soft, spongy tissue called bone marrow. It looks unimpressive - kind of like raw chicken filling - but it does an incredible job. Bone marrow is where your body produces most of your blood cells, and it never stops.
Adult human bone marrow makes about 2 million red blood cells every second. Plus white blood cells (for fighting infections), and platelets (for clotting wounds). Every type of blood cell traces back to “hematopoietic stem cells” living in the marrow. As you read this, those stem cells are producing the fresh blood you’ll be using tomorrow.
This is also why bone marrow donations matter so much medically. Diseases like leukemia damage the marrow’s stem cells, leaving patients unable to make their own blood. A transplant of healthy stem cells from a donor - sometimes just a small sample of marrow from the hip - can completely restore the patient’s ability to make blood. It’s one of the most powerful treatments in modern medicine.
