Bone
Bone cells
Osteoprogenitor:
mesenchymal cells that di.eren0ated into osteoblast.
Structure - Fla8en cells.
Loca0on - located in the cellular layer of the periosteum, endosteum and Harversian canal.
Osteoblasts (bone building cells):
Synthesize and secrete collagen Abers and other organic components of bone matrix.
Cuboidal or columnar cells.
Loca0on – line all trabeculae from the surface side.
Osteocytes (mature bone cells):
No longer secrete matrix and Responsible for maintaining the bone 0ssue.
Loca0on – located in spongy and compact bone (cell body located within lacunae and
cytoplasmic process within canaliculi)
Structure - Elongated Ka8ened in comparison to osteoblast.
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Osteoclasts (bone destroying cells):
Secret enzymes which digest bone matrix (bone resorp0on- part of normal bone growth,
development, maintenance, and repair).
Loca0on – located within Howship’s lacunas (compact and spongy bone).
Structure - Very large, branch, mo0le and mul0nucleated.
Origin – Fusion of mononuclear Hemopoe0c progenitor cell / Fusion of monocytes.
Bone matrix
Organic compounds:
90% Type 1 collagen.
Proteoglycans.
Bone sialoprotein.
Inorganic compounds:
Hydroxyapa0te crystals (Ca phosphate & calcium hydroxide).
Ions of Na, Mg, Fe.
, Periosteum
Covering of the external surface of the bone and has 2 layers:
Fibrous layer – thick outer layer contains dense connec0ve 0ssue (bundles of collagen
Abers, Abroblasts).
Osteogenic layer – more cellular layer of the periosteum, where Osteoprogenitor develop
to osteoblasts (developing and repairing take place).
Compact bone (dense areas without cavi?es)
Lamella: layer of bone matrix, embedded with collagen Abers and btw them there are
lacunas with osteocytes.
There are 4 types of lamella –
Outer circumferen0al – located immediately beneath the periosteum.
Inters00al lamella – incomplete lamella between the osteons.
Concentric lamella - encircles the Haversian canal and build up the osteon.
Inner circumferen0al – located around the marrow cavity, above the endosteum.
Osteon:
DeAni0on - Basic func0onal unit of compact bone, each osteon consists of Concentric
lamellae that surround Haversian canal.
Structure –
Cement: The boundary of each osteon.
Concentric lamella
Canaliculi: canals btw lacunas which leading to the Haversian canal.
the cytoplasmic processes of the osteocytes project into these canals.
Lacunae: spaces btw the lamellas where cell bodies of osteocytes are located.
Haversian canal: occupies blood vessels and nerves.
Volkmann's canal: perpendicular to the Haversian. Connects the blood and nerve supply
from the periosteum to those in the Haversian.
Bone cells
Osteoprogenitor:
mesenchymal cells that di.eren0ated into osteoblast.
Structure - Fla8en cells.
Loca0on - located in the cellular layer of the periosteum, endosteum and Harversian canal.
Osteoblasts (bone building cells):
Synthesize and secrete collagen Abers and other organic components of bone matrix.
Cuboidal or columnar cells.
Loca0on – line all trabeculae from the surface side.
Osteocytes (mature bone cells):
No longer secrete matrix and Responsible for maintaining the bone 0ssue.
Loca0on – located in spongy and compact bone (cell body located within lacunae and
cytoplasmic process within canaliculi)
Structure - Elongated Ka8ened in comparison to osteoblast.
***********************************
Osteoclasts (bone destroying cells):
Secret enzymes which digest bone matrix (bone resorp0on- part of normal bone growth,
development, maintenance, and repair).
Loca0on – located within Howship’s lacunas (compact and spongy bone).
Structure - Very large, branch, mo0le and mul0nucleated.
Origin – Fusion of mononuclear Hemopoe0c progenitor cell / Fusion of monocytes.
Bone matrix
Organic compounds:
90% Type 1 collagen.
Proteoglycans.
Bone sialoprotein.
Inorganic compounds:
Hydroxyapa0te crystals (Ca phosphate & calcium hydroxide).
Ions of Na, Mg, Fe.
, Periosteum
Covering of the external surface of the bone and has 2 layers:
Fibrous layer – thick outer layer contains dense connec0ve 0ssue (bundles of collagen
Abers, Abroblasts).
Osteogenic layer – more cellular layer of the periosteum, where Osteoprogenitor develop
to osteoblasts (developing and repairing take place).
Compact bone (dense areas without cavi?es)
Lamella: layer of bone matrix, embedded with collagen Abers and btw them there are
lacunas with osteocytes.
There are 4 types of lamella –
Outer circumferen0al – located immediately beneath the periosteum.
Inters00al lamella – incomplete lamella between the osteons.
Concentric lamella - encircles the Haversian canal and build up the osteon.
Inner circumferen0al – located around the marrow cavity, above the endosteum.
Osteon:
DeAni0on - Basic func0onal unit of compact bone, each osteon consists of Concentric
lamellae that surround Haversian canal.
Structure –
Cement: The boundary of each osteon.
Concentric lamella
Canaliculi: canals btw lacunas which leading to the Haversian canal.
the cytoplasmic processes of the osteocytes project into these canals.
Lacunae: spaces btw the lamellas where cell bodies of osteocytes are located.
Haversian canal: occupies blood vessels and nerves.
Volkmann's canal: perpendicular to the Haversian. Connects the blood and nerve supply
from the periosteum to those in the Haversian.
