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 frontal section through the face of an embryo contains many examples of intramembranous bone formation. Bone is formed by the differentiation of mesenchymal cells into osteoblasts.
Osteoblasts - cover the surface of bone spicules. Their 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 bone.
These spicules are examples of woven immature (or primary) bone. They contain randomly arranged type I collagen fibers within a more basophilic, mineralized osteoid.
Other interesting structures unrelated to intramembranous bone formation.
Merkel's Cartilage (left, right) - occurs transiently in human embryos. It forms the jaw in cartilaginous fish.
Endochondral Bone Formation - the cartilaginous scaffold of the developing septal bone, ethmoid bone (left, right) and nasal conchae (left, right) are seen.