what is a bone marrow
Bone marrow is the flexible tissue in the interior of bones. In humans, red blood cells are produced by cores of bone marrow in the heads of long bones in a process known as hematopoiesis.On average, bone marrow constitutes 4% of the total body mass of humans; in an adult weighing 65 kilograms (143 lb), bone marrow typically accounts for approximately 2.6 kilograms (5.7 lb).he two types of bone marrow are red marrow (Latin: medulla ossium rubra), which consists mainly of hematopoietic tissue, and yellow marrow (Latin: medulla ossium flava), which is mainly made up of fat cells.