Bone Metabolism W4 Flashcards
Structure of a cortical bone
Also called compact bone is the dense outer layer of bone that provides strength and support. Contains:
- osteons
- Haversian Canal
- lamellae
- volkmans canals
- lacunae
- canaliculi
- periosteum
- endosteum
- osteons
fundamental structural unit of cortical bone.
Each osteon is a cylindrical structure running parallel to the bone’s long axis.
Contains concentric layers (lamellae) of bone matrix surrounding a central canal.
- Haversian Canal
Located at the center of each osteon.
Contains blood vessels, nerves, and lymphatic vessels that nourish the bone.
- lamellae
Concentric lamellae: Surround the Haversian canal in rings.
Interstitial lamellae: Found between osteons, remnants of older osteons.
Circumferential lamellae: Found at the outer and inner surfaces of the bone, reinforcing its structure.
- volkmans canals
Run perpendicular to Haversian canals.
Connect blood vessels and nerves between adjacent osteons and the bone surface.
- lacunae
Small spaces between lamellae that house osteocytes (bone cells).
- canaliculi
Tiny channels connecting lacunae.
Allow communication and nutrient exchange between osteocytes.
- periosteum
A tough outer membrane covering the bone, except at joint surfaces.
Contains blood vessels, nerves, and osteogenic cells (for bone growth and repair).
- endosteum
A thin membrane lining the inner surface of the bone (medullary cavity).
Contains bone-forming and bone-resorbing cells.
Cells of the bone
Osteoblast
Osteoclast
Osteocyte
Osteocytic-osteoblastic bone marrow
Bone fluid
Mineralised bone
The majority of the bone comprises….
hydroxyapatite
crystals ( Ca10(PO4)6(OH)2) which precipitates
around the collagen extracellular matrix (the osteoid)
in the bone
Bone turnover
Osteoclasts dissolve the bone -> Osteoclast dies or migrates -> Osteoblasts fill the cavity
Osteoclast numbers are controlled by…
Factors from the osteoblast :
- RANKL
- Osteoprotegerin
- RANKL
increases osteoclast differentiation and decreases
osteoclast apoptosis, increasing their number and
promoting bone resorption over the long-term
Osteoprotegerin
is a “decoy” receptor for RANKL.
It therefore decreases osteoclast number and promotes
bone deposition over the long-term
The balance of RANKL and OPG are importantly…
Determinate of bone density
Oestrogen and OPG
Oestrogen stimulates production of OPG and promotes apoptosis of osteoclasts and increases the number of osteoblasts
