Bone Flashcards
What is the main functional unit of the cortical Bone?
Haversion System (secondary osteon)
What structure is the wall of the haversion system?
Concentric lamellae
Whats in the central canal of the haversion system?
Haversian canal, nerve and blood supply
What is the main cell component of the haversion system?
Osteocytes
What is between osteons?
Interstitial lamellae
What is the connection between osteons?
volkmanns canals
What are the small spaces that connect to lacunae?
canaliculi which are small pathways for the processes of the osteocytes
What is in the bone matrix?
Inorganic and organic matrix
What is the inorganic and organic matrix composed of?
inorganic matrix: HA
Organic: Collagen I
What are the 2 lineages of bone cells?
First: Mesenchymal lineage (give rise to osteoprogenitor cells –> preosteoblast –> osteoblast –> osteocytes and lining cell.
Second: Hematopoeitic lineage (Cells give rise to monocytes/macrophage and the osteoclasts are the mature form of these cells.)
What else are mesenchymal stem cells referred to as? some characteristics
colony forming fibroblasts. or Marrow stromal cells.
can differentiate into multiple cell types
small cell body and few cell processes.
must stain many biological markers to see what kind it is.
Osteoblasts
Bone forming cells.
Basic characteristics of Osteoblasts
Produce a lot of alot of proteins Located on bone surface Generally cuboidal Mononucleated HE staning: Basophilic cytoplasm (bc of a large amount of Rough ER--make proteins)
first Major functions of Osteoblasts
synthesize and secret extracellular matrix. and a fuck ton of other proteins.
MAKE collagen type I mainly.
second function of osteoblasts
Regulate matrix mineralization.
- releases matrix (osteoid) and minirlizes it by calcification. This process is regulated by osteoblasts.
- This is done By releasing matrix vesicles (have high CA and Phosphorous in cytosol without being saturated) into osteoid and calcifying it over time.
Third major function of osteoblasts
Regulates osteoclasts (take bone away) through molecular interactions.
what do osteoblasts release to regulate osteoclasts
RANKL: stimulates osteoclast differentiation and maturation (used for bone resorption)
OPG: binds to rankle and indirectly inhibits osteoclast differentiation. aka reduces bone resorption activity.
Osteocytes
bone-maintaining cells. Derived from osteoblasts when buried in the matrix. Located in laculae inside the matrix.
Most abundant cell type in bone
osteocytes
T/F Osteocytes are mononucleated
true
T/F Osteocytes have few dendritic processes
FALSE have multiple
Main function of osteocytes
- regulate osteoblasts and osteoclasts through cell processes.
- They maintain bone vitality and fucntion. If osteocytes are dead bone is dead too.
- Sense mechanical loading… decide if they should produce more bone or decrease it.
How do osteocytes handle mechanical loading
after sensing loading, they regulate bone formation/resorption mainly through the schlerostin-OPG/RANKL system.
Is schlerostin expressed in all bone cells?
no only in OSTEOCYTES
Osteoclasts (8)
- Bone resorption cells (through organic matrix degradation)
- Largest of all bone cells
- Located on bone surface (howships lacunae)
multinucleated - TRAP (enzyme) positive cytoplasm
- lots of mitochondria
- Sealing zone (attachment and sealing)
- Demineralize bone
- Endocytosis of degraded products
Two forms of bone formation
- one through membrane–> intramembranous ossification (directly from periosteum)
- one through cartilage –> Endochondral ossification
Sutural bone formation
A special intramembranous process through sutural matrix. This bone formation is a intramem. mechanisim. very similar to periosteum. No cartilage involved.