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marrow (marŽo) soft spongy material; called also medulla. The term is often restricted to mean bone marrow. bone marrow
the soft, spongy material in the cavities of bones, consisting of a network of blood vessels and connective tissue fibers
that hold together fat and blood-producing cells. Its chief function is to manufacture erythrocytes, leukocytes, and platelets; these blood cells normally do not enter the bloodstream until they are fully developed, so that the marrow contains many
immature cells. There are two types of marrow, red and yellow. red bone marrow
marrow of developing bone, of the ribs, vertebrae, and many of the smaller bones; it is the site of production of erythrocytes and granular leukocytes. In early childhood, all bone marrow is red; as a person gets older, the fat content of the marrow increases and much of
it turns from red to yellow. yellow bone marrow
bone marrow in which fat cells are dominant; this portion normally has no blood-producing function. Red marrow predominates
in childhood, but as a person gets older, the fat content increases and most of the bone marrow changes from red to yellow.
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