L10. Bone Flashcards
What are the similarities between bone and cartilage
- both have a dense irregular CT acts as a protective layer
bone : periosteon
cartilage: perichondrian - specialized forms of the connective tissue
- derived from the mesenchymal layer of the embryo
- cells are embedded in the matrix (ECM) in the lacunae
- function rely on the ECM composition
What are the differences between bone and cartilage
- cartilage is not vascularized , bone has blood vessels
- bone is mineralized and solid, cartilage is gel-like and hydrated and firm
- cartilage has a high diffusion index, bone does not
- bone is easily regenerated, cartilage is not
where do blood vessels enter the bone
They enter at the end of the bones (epiphyseal) and the middle of the long bone ( diaphysis).
Draw a fully form long bone
Include: articular cartilage, growth plate, diaphysis, epiphysis
L10, pg 2b
What is osteoid?
It is the organic component of bone
What is the inorganic component of bone called?
Mineralized
What deposits osteoid ( 35% of the bone)
osteoblasts deposit the osteoid
Describe the Osteoid which is the organic substance that makes up 35% of the bone
- collagen type 1 fibers
- low amount of diffusion
- low amount of ground substance, some proteoglycan and glycoprotein that binds integrins
What does collagen part 1 fiber stain in HE
It is acidophilic and stains pink (eosin)
What composes the ECM of the bone
contains 35% of osteoid (organic material) and 65% of inorganic mineralized substance
How is the inorganic portion of the ECM of bone made?
osteoclast and osteoblast come in later and form hydroxyapatite on the collagen fibers extracellularly in the lacunae
alkaline phosphatase enzymes comes in to facilitate bone deposition activity
what is in the mineralized ECM of the bone?
consists of hydroxyapatite crystals ( high in Ca 2+ and phosphate)
rigid
low amount of diffusion
Where do the osteocyte and osteoblast develop?
The osteocyte and osteoblast develop in the dense irregular CT that surrounds the bone ( periosteum)
What is the lineage for osteoblast?
mesenchymal cell-> osteoprogenitor -> osteoblast-> osteocytes
How is the periosteum attached to the bone?
Collagen bundles attach the periosteum to the bone
How many layers does the periosteum have, what are they?
2 layer: outer fibrous layer, inner cambium layer
outer fibrous layer: dense irregular CT
inner cambium layer: osteoprogenitors and osteoblasts
What is the periosteum?
It is a protective covering of external surface of the bone
What stimulates osteoprogenitor lineage differentiation?
- paracrine factors by fibrocytes in the CT
- endothelial cells
- pericytes of vasculature
- bone morphogenic protein
- transforming growth factor
Describe the osteoprogenitors
- flattened ,elongated
- restricted lineage
- ste activity ( proliferate and differentiate)
- from mesenchymal cells
Describe the osteoblasts
- cuboidal
- matrix secreting machinery directed to attached surface of the cell (integrin dependent)
- prominent RER ( stains blue in HE)
Describe the osteocytes
stellate shape
- in lacunae
- send out processes through cannaliculi
- communicates with other cells through gap junctions
What are canaliculi
Small tunnels in the lacunae osteocytes used to send processes
What are osteoclasts?
- large, multinucleated
- from hematopoietic stem cells
- absorb, digest , destroy bone matrix ( the ECM set by the osteoblasts)
- needed for bone remodelling/repair
- control Ca2+ levels
Where do osteoclasts come from?
hematopoietic Stem cells
How does osteoclasts regulate calcium levels in blood
Breaks down hypoxyapetate crystals to release Ca2+
What is spongy bone?
Consists of small connected pieces of bone tissue ( spicules)
Where is the osteoblast located in the spongy tissue, what does it do?
The osteoblast is located on the edges of the bone tissues (spicule). Osteoblast lays down the matrix ( organic osteoid layer)
Where is the osteocyte located in the spongy tissue, what does it do?
The osteocyte is located in the lacunae
- lays down the mineralized crystals
What stimulates the osteoclast
Osteoblasts due to the action of parathyroid hormone ( increase the blood Ca2+ levels)
What inhibits osteoclast’s action>
Calcitonin and Bisphosphonates
How do osteoclasts bind to bone?
Osteoclasts binds to bone with focal adhesions and actin filament
What is the sealing zone
It is where the osteoclasts binds to the bone and reabsorption occurs
How does osteoclasts function to reabsorp bone?
- Carbonic anhydrase in the cytoplasm makes carbonic acid
- H+ enters the sealing zone between the bone and osteoclast via transmembrane channels. Acid degrades hydroxyapitite which releases calcium.
- Ca2+ picked up by capillaries to increase Ca2+ levels
- cells release lysozymes to degrade the collagen and osteoid
What is the difference between compact bone and spongy bone?
compact bone: bundles of osteons, dense outer layer of the bone
spongy bone: central portion of the bone, interconnected struts of bone tissue, interface with bone marrow
What are osteons?
closely packed concentric layers of bone tissue that form in the compact bone
Describe the compact bone structure
bone matrix (the ECM with osteoids and mineralized stuff) is arranged in concentric layers around a central canal - forms cylindrical layer of bone tissue ( osteons) with a central Haversian canal and Volksmann canal
What is the difference between a Haversian and Volksman canal
Found only in the compact bone. Haversian canals are vertical, Volksman are transverse
What are the 2 ways bone is formed?
- intramembranous bone formation
2. endochondrial bone formation
When is intramembranous bone formation needed?
flat bone formation ( skull )
Describe intramembranous bone formation
- mesenchyme condenses
- mesenchyme stem cells produce osteogenic lineage
- bone forms directly from the mesenchyme
Identify all structures ( osteocytes, osteoblasts, mesenchyme cells, collagen and osteoid, trabculae ) on figure 7-13 (page 146 of TB
or Page 8 of L10 notes
What is the process of endochondrial bone formation
- hyaline cartilage is formed as the primary structure
- blood vessels invade the cartilage and drag in osteoprogenitors cells with them
- increased oxygenation leads to eventual chondrocyte death and the calcification of the cartilage.
- bone tissue is laid down in place of dead chondrocytes ( ossification center)
- primary ossification occurs in the middle of the long bone ( diaphysis) then at the ends of the long bone ( epiphysis)
- reserve cartilage remains between the diaphysis and the epiphysis through puberty
- growth plate expands until early adulthood , the growth plate eventually calcifies and becomes bone
what is osteoporosis?
- An increase in bone porosity
- increased risk of fracture
- bone remodeling skewed towards greater bone resorption
- treatment: anti-resorptives and anabolics
- want a decrease osteoclast activity (use bisphosphates)
What is distant site osteolytic metastasis?
Lesions that originate in other tissues travel to the bone where they activate the osteoclasts and bone is destroyed
What can be used to treat osteolytic metastasis?
Anti-resorptives decrease the activity and alleviate much of the pain:
- decrease the paracrine release factors from the bone matrix (transforming growth factor)
What does the transforming growth factor beta do?
- With calcium stimulates the growth and paracrine factor release of the mestastic tissue cells
- stimulates osteoprogenitor growth differentiation
How do antiabsorptves block the metastatic cycle?
PTHrP= Parathyroid hormone related peptide produced by the tumor cells stimulate osteoblasts to make RANKL.
- RANKL stimulates osteoclast differentiation
- Bisphosphate which mimics hydroxyaptite but cannot be broken down slows the viscous cycle
- Denosuman (Prolia) is an antibody that is directed against RANKL to block osteoclast
