OSTEIOCLASTS
how does ostoeclasts form?
from hematopoetic stem cells- myeloid progenitor- granulocyte macrophage progenitors- forms macrophages, granulocytes, dendritic cells, osteoclasts
osteoblast products
what are the products produced by osteoblasts
Type 1 collagen and non collagenous proteins like- osteopontin, osteonectin, osteocalcin, alkaline phosphatase, bone sialoprotein
osteoblast turn to?
what does osteoblast convert into?
if it gets embedded in the matrix, it forms osteocyte and resides inside lacunae. Others become flattened cells on bone surface, called** lining cells. **
60-80% undergo apoptosis
lining cells
function of lining cells in osteoclast formation?
Communicate with osteocytes and promote differentiation of hematopoietic stem
cells into osteoclasts.
osteocytes
3 interestng facts of osteocytes
- Do not divide.
- Have an average half life of 25 years (the longest lived of all bone cells).
- The most commonly found cells in mature bone tissue
osteocyte
Osteocyte network?
- They communicate with nearby osteocytes,
osteoblasts, osteoclasts. - They exchange nutrients and waste through gap
junctions
osteocyte function
name some functions of osteocytes
- Capable of sensing and integrating mechanical
and chemical signals from their environment. - Control the activity of osteoblasts and
osteoclasts- Regulate both bone formation and resorption. - Capable of molecular synthesis (Sclerostin, DKK1)
DKKI- dickkopf-related protein 1 plays a crucial role in regulating the Wnt signaling pathway
MSC
what are the cells formed from MSC?
Mesenchymal stem cells (MSC) - mesenchymal progenitor cells-
Angiogenesis- Endothelial cells
Adipogenesis- Adipocytes
Chondrogenesis- Chondrocytes
Myogenesis- Myocytes
Osteogenesis- Osteocytes
MSC
Where do MSCs
reside?
- Bone marrow
- Periosteum
- Along vascular
channels
bone components
what is bone formed of largely? what % is organic and inorganic?
**Inorganic (mineral)- 70%- Hydroxyapatite
Organic (collagen)- 30% **
- Elastic collagen- 90-95%
- ground substance- (proteinpolysaccharides,
glycoaminoglycans etc.)
whats the ideal mineral-collagen ratio?
Optimal ratio 66%-34%
woven bone
what is woven bone? histolgy?
- Its fibrous bone- relatively weak, disorganized
and poorly mineralized - Not found in the adult skeleton under normal, steady-state conditions.
- It is remodeled to lamellar bone, or rapidly resorbed
if prematurely loaded.
Histology- ** Hypercellular**; Osteocytes are large and distributed randomly. Collagen fibers are oriented differently
woven bone
what are the functions of Woven bone?
crucial role in wound healing.
- Rapidly fills osseous defects
- Provides initial continuity for fractures and osteotomy segments.
- Strengthens a bone weakened by surgery or trauma.
The first bone formed in response to orthodontic loading.
The first bone formed in response to orthodontic loading.
lamellr bone
what is lamellar bone?
- Secondary bone created by remodeling
of woven bone. - Makes up more than 99% of the adult
human skeleton. - Stronger; Highly-organized; Well-mineralized, less cellular
- Osteocytes and their lacunae are smaller.
- Collagen lamellae are regularly
oriented.
The full strength of lamellar bone that supports an orthodontically moved tooth is not achieved until about 1 year after completion of
active treatment.
bone
classify bone
based on composition/tissue type- woven and lamellar
based on structure- Cortical (Compact) bone and Trabecular (cancellous) bone
what are osteons?
- Fundamental functional units of compact bone.
- Roughly cylindrical structures (50-100 μm
in diameter) - Each osteon consists of lamellae that surround
the haversian canal. - Connected to each other by Volkmann’s canals
The haversian canal contains the bone’s blood supplies.
In trabecular bone, trabeculae are arranged in order or not?
- Trabeculae are arranged in an orderly pattern
- Provide maximal rigidity with minimal material
- Porous bone - Houses blood vessels and
red bone marrow.
Periosteum
what are the layers of periosteum?
Outer
(fibrous) layer
Inner
(cellular) layer
what is the main function of osteoblasts?
to form bone matrix
