​OSTEOCLASTS - a large multinucleated bone cells that absorb bone tissue during growth and healing.

​OSTEOBLASTS - cells that form new bones and grow and heal existing bones.

​OSTEOCYTES - these cells are derived from osteoblasts, they exist within the bone matrix and help to nourish bone tissue and regulate other bone cells

​Osteoid is an unmineralized organic tissue that eventually undergoes calcification and is deposited as lamellae or layers in the bone matrix.

​Osteoblasts group into clusters and form an ossification center. Osteoblasts begin secreting osteoid, an unmineralized collagen-proteoglycan matrix that can bind calcium. The binding of calcium to osteoid results in the hardening of the matrix and entrapment of osteoblasts. This entrapment results in the transformation of osteoblasts to osteocytes. As osteoid continues to be secreted by osteoblasts, it surrounds blood vessels, forming trabecular/cancellous/spongy bone. These vessels will eventually form the red bone marrow. Mesenchymal cells on the surface of the bone form a membrane called the periosteum. Cells on the inner surface of the periosteum differentiate into osteoblasts and secrete osteoid parallel to that of the existing matrix, thus forming layers. These layers are collectively called the compact/cortical bone.

​nih.gov

​The fontanel closes via ossification. During ossification the following happens

• Epiphysis - end of a long bone.

• Diaphysis - shaft of a long bone.

• Medullary (Marrow) Cavity - space in the middle of the diaphysis.

• Periosteum - Lining of the outside of the bone.

• Endosteum - Lining of the medullary cavity. Contains yellow marrow.

• Spongy Bone - porous bone at the epiphysis. Contains red marrow.

• Compact Bone - dense and strong bone that makes up the diaphysis.

​Simple fractures - bruising, immobility, no broken skin

Compound fractures - bone is so displaced that it breaks the skin.

Greenstick fractures - usually happen in young children

Comminuted fractures - there is debris between the two pieces of a broken bone

Impacted - pieces of a broken bone are "telescoped" on each other

​Osteoporosis is a disorder that happens when the body takes too many minerals out of storage in the bones. Osteoporitic bones are more porous and more fragile because they don't contain enough calcium and phosphorous.



Since the bones are more fragile, they are more likely to break. Older women are more likely to have osteoporosis than anyone else.