Bone, cancellous, decalcified 40X
 
Cancellous or spongy bone has a much simpler structure than compact bone. The structural units are called trabeculae (tr). They are small, irregularly shaped slivers of bone that are attached to each other at their ends. This leaves spaces in the tissue that give the bone its name of "spongy". Spongy bone is in the upper left portion of the image, and compact bone (cb) is in the lower right. It would be difficult to confuse spongy bone with other tissues because of the distinctive and irregular shape of the trabeculae.

Bone, cancellous, decalcified 100X
 
The trabeculae (tr) consist of matrix that is made by osteoblasts. The bone cells build a trabecula by adding layers of matrix on the outside of the trabecula. This continues until it runs into another growing trabecula, and they fuse together. You can see pale lines in the trabecula in the center of this image. The lines are a result of building up the trabecula layer by layer. The spaces between the trabecula are filled with active or inactive bone marrow. Since this bone has adipose tissue in the spaces, the bone marrow in this area was inactive.

Bone, cancellous, decalcified 400X
 
The osteocytes (o) of cancellous or spongy bone are also found in spaces called lacunae. The layers of matrix are very clear on this image.










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