T. Clark Brelje, Ph.D.
University of Minnesota
Department of Genetics, Cell Biology and Development
6-160 Jackson Hall
321 Church St SE
Minneapolis, MN 55455
Robert L. Sorenson, Ph.D.
University of Minnesota
Department of Genetics, Cell Biology and Development
6-160 Jackson Hall
321 Church St SE
Minneapolis, MN 55455
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This section contains many areas of intramembranous bone formation. Bone is formed by the differentiation of mesenchymal cells into osteoblasts.
Examine the region with newly formed, basophilic bone:
Osteoblasts - cover the surface of bone spicules. Their very basophilic cytoplasm is from the synthesis of proteins in osteoid (mostly type I collagen).
Osteoid - unmineralized, organic portion (type I collagen and ground substance) of bone matrix. Narrow, light-pink region between osteoblasts and the bone spicule.
Osteocytes - osteoblasts trapped inside lacunae of the bone.
The spicules are examples of woven immature (or primary) bone. They contain randomly arranged type I collagen fibers within a basophilic, mineralized osteoid.
The spicules fuse with each other and from trabeculae. These provide the general shape of the developing bone.
There is little evidence of osteons found in mature (or secondary) bone. A few developing osteons (#1 and #2) can be recognized by blood vessels at the center of an area surrounded by osteoblasts.