Ch 6 Bone Matrix/Cells

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Osseous tissue
dense, supportive connective tissue
containing specialized cells
Produces solid matrix of calcium salt deposits
Around collagen fibers
characteristics of bone tissue
1. Dense matrix containing deposits of calcium salts
2. The matrix contains bone cells within lacunae, which are organized around blood vessels.
3. Canaliculi form pathways for blood vessels to exchange nutrients and wastes.
4. Outer surfaces of bones are covered by periosteum consisting of outer fibrous and inner cellular layers.
Canaliculi
Form pathways for blood vessels
Exchange nutrients and wastes
periosteum
covers outer surface of bones
Consists of outer fibrous and inner cellular layers
matrix minerals
calcium phosphate
protein fibers (collagen)
bone cell types
osteocytes, osteoblasts, osteoprogenitor cells, osteoclasts
Osteocytes
Mature bone cells that maintain the bone matrix.

Each lives in a lacuna between layers (lamellae) of matrix.
Canaliculi through the lamellae allow for connect at gap junctions between cytoplasmic extensions.

They do not divide.
Osteocytes function
To maintain protein and mineral content of matrix
To help repair damaged bone
Osteoblasts
immature bone cells that secrete the matrix by the process of osteogenesis
Osteoblasts surrounded by bone
become osteocytes
Osteoid
matrix produced by osteoblasts, but not yet calcified to form bone
Osteoprogenitor cells
Mesenchymal stem cells that divide to produce osteoblasts
Are located in endosteum, the inner, cellular layer of periosteum
Assist in fracture repair
Osteoclasts
cells that remove and recycle bone matrix
Giant, multinucleate cells
Are derived from stem cells that produce macrophages
Secrete acids and protein-digesting enzymes
Bone homeostasis
Bone building (by osteoblasts) and bone recycling (by osteoclasts) must balance
bones weaken
when osteoclasts remove calcium salts faster than osteoblasts deposit them
Bones become stronger bigger
when osteoblasts activity predominates
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