What is bone marrow? So the bone marrow is found in our bones. It's found in the inside cavity of our bones. It's most prevalent in the long bones and large bones. So the largest marrow reservoirs in the body would be in like the humerus, the femurs, and the pelvis, and some in the sternum. The bone marrow is like a reticular bone, so it's kind of lacy or porous. And in that matrix structure is where our blood cells are made. So that's the primary responsibility of the bone marrow. It's our blood making system. So all of our blood cells are made in the bone marrow. So red blood cells, white blood cells, and platelets are made there. And then we find the precursor cells of those cells in the bone marrow as well. So precursor stem cells for platelets, red blood cells, and white cells. So it's found all over the body. The bone marrow itself is just full of these baby cells and stem cells that make our blood system. And that tissue is very fatty because it's really energy rich and those cells need a lot of energy. And so there's a lot of fat in the bone marrow.