Bone Marrow

Bone Marrow is present in the medullary cavity of the bone. There are two types of bone marrow- red and yellow bone marrow.

Red bone marrow

Red Marrow occupies the interstices of spongy bone everywhere and medullary cavity of long bones at birth. After birth, the red marrow is gradually replaced by yellow marrow.

It is an important blood forming substance and contains precursors of erythrocytes, granular leukocytes of the blood, giant cells, which give rise to platelets and a few fat cells.

In the adult, red marrow is present only in the vertebrae, sternum, ribs, skull bones and epiphyses of long bones.

Yellow bone marrow

Yellow Marrow consists of ordinary adipose tissue especially in the medullary cavity of long bones and short bones.

Yellow bone marrow fills the spaces of the spongy bone in short bones (carpals and tarsals) and medullary cavity of long bones.