red marrow [AS, read + AS, mearh, marrow] , the red vascular substance consisting of connective tissue and blood vessels containing primitive blood cells, macrophages, megakaryocytes, and fat cells. It is found in the cavities of many bones, including flat and short bones, bodies of the vertebrae, sternum, ribs, and articulating ends of long bones. Red marrow manufactures and releases leukocytes, erythrocytes, and thrombocytes into the bloodstream. Compare yellow marrow.
