Lecture 7-Bone Flashcards
In evolution, skeletons began to appear after the evolution of what? Why?
- carbonic anyhydrase
- allows deposition of Ca
What are the similarities between bone and cartilage? (3)
- both hard tissues
- have living cells in lacunae (matrix)
- arise from mesenchymal cells
What are the differences between bone and cartilage? (2)
- bone is heavily vascularized
- bone has access to blood vessels via canaliculi while cartilage is less calcified so uses long range diffusion
What external factor dictates whether cartilage or bone will form from mesenchymal cells?
- presence/absence of O2: if O2 is present then bone forms, if absent, then cartilage forms
Bone is a dynamic tissue in that it _____
is constantly remodeling/turning over
What is the effect of mechanical stress on bone?
- allows for proper bone remodeling since it has plasticity which is exploited by orthodontists
- without the mechanical stress there can be loss of bone during flight or immobilization
What is the piezoelectric potential? What does a (+) and (-) potential mean?
- electric potential generated in bone by pressure on the hydroxyapatite crystals and cell membranes
- Pressure on the crystals causes a (+) potential: bone reabosrption
- (-): bone deposition
How much of bone is fibrous (inorganic) vs. organic?
- 75% is inorganic/fibrous
- 25% is organic
Describe the composition of the organic component of bones
- Fibers: 90% type I collagen
- Ground substance: Glycosaminoglycans (chondroitin and keratan sulfates); glycoproteins
Does the bone MATRIX have cells?
no
Osteonectin and osteopontin fall under what classification? What are they?
- glycoproteins of the organic component of bone
- anchor minerals to collagen and in initiate mineralization/crystal formation
Osteocalcin and bone sialoprotein
- types of glycoproteins in the organic component of bone
- Ca binding proteins
What are the glycoproteins of the organic component of bone?
- osteonectin and osteopontin
- osteocalcin and bone sialoprotein
What is osteoid?
- part of the organic component of bone
- newly secreted organic matrix that’s not yet fully calcified
Describe the inorganic composition of bone. (6)
- comprises 50-70% of bone
- mostly CaPO3 salts in amorphous or crystalline form
- also hydroxyapatite (Ca10(PO4)6(OH)2)
- Ca citrate
- bicarb
- Fl
Water makes up __% of bone mass
15
What is the hydration shell?
- in the inorganic component of bone
- surrounds hydroxyapatite crystals and facilitates with Ca exchange with fluids
- major source of blood Ca
Mineralized bone matrix is deposited where? Describe the 2 different types of these.
- in layers called lamellae
- Spongy/cancellous: spicules or trabeculae with large marrow spaces in between
- Compact/cortical bone: more elaborate architecture with circumferential lamellae and cylindrical columns called osteons/Haversian systems. These also contain interstitial lamellae
What are 2 ways to prepare bone sections for microscopy?
- decalcification leaving only organic material but flexible and with the same shape
- grinding into translucent sections; can see the arrangement of bone
Mesenchymal cells differentiate into ____
osteoblast –> osteocyte –> cartilage or bone
Osteoblasts (3)
- secrete organic material like type I collagen and amorphorous substance to make osteoid
- non-dividing
- highly secretory (and therefore lots of RER and golgi)
osteoid
- incompletely ossified material
osteocytes (3)
- mature osteoblasts trapped in their own material (osteoid-eosinophilic) called lacunae
- terminally differentiated therefore reduced RER and golgi
- extend filopodia in canaliculi
osteoclasts (5)
- multinucleated cell formed by VitD promoted fusion of monocytes/macrophages that function in bone reabsorption
- non-dividing
- mobile
- located on bone resorptive and free surfaces in cavitations called Howships lacunae (since they’re chewing away at the bone)
- Ruffled borders to increase SA for bone reabsorption
osteogenic cell
another name for mesenchymal osteoprogenitor, a committed mesenchymal cell
Committment of osteogenic cells (mesenchymal cells) is controlled by what? (2)
- BMP (bone morphoenic protein)
- osteogenin
Self renewal of osteogenic cells is controlled by what factors? (3)
- PDGF
- TGF beta
- IGF
Differentiation of osteogenic cells (mesenchymal cells) is controlled by what factors? (2)
- BMP
- VitD3
How do BMP levels change with age?
decreases
What stimulates osteoblast secretion of osteoid?
- GH (somatotropin)
- sex steroids
Bone apposition
- deposition of osteoid between osteoblast layer and existing bone
VitD of Ca deficiency results in what?
osteomalacia/poor mineralization
Canaliculi
osteocytes extend their filapodia through these, they are canals connecting cells (i.e., gap junctions) and can exchange nutrients
Osteocyte osteolysis
- reduced Ca release in lacunae
What increases osteocyte osteolysis and what decreases it?
- PTH increases reabsorption and therefore this
- Cacitonin from thyroid decreases resorption and therefore this
Osteocytes are only found where?
- in compact bone
What are the 2 mechanisms by which osteoclasts cause bone resorption. Explain the process.
- focal decalcification: acidification of the immediate environment by citric acid, bicarb (formed by CO2 and H2O) and carbonic anhydrase (at ruffled border). Partial degradation of CaPO3 by H ions. These remnants are taken back up by osteoclasts and transported to bvs and therefore other parts of the body.
- extracellular digestion: by hydrolytic enzymes collagenase (degrades type I collagen which is the major part of fibrous component), acid phosphatase and sulfatase
Which 2 parts of the bone make up the bone proper?
- periosteum (think of this as the bone equivalent to perichondrion)
- endosteum
What are the 2 parts of the periosteum? Describe both.
- fibrous periosteum: outer fibrous layer, highly vascularized
- osteogenic periosteum: inner cellular layer with osteogenic cells (mesenchymal) and osteoblasts
How does the periosteum attach to bone?
- collagen fibers called Sharpey’s fibers that originate from the Volkmann’s canals which contain blood vessels
Describe the endosteum of the bone.
- single cell layer of progenitor cells, osteoblasts and osteoclasts that lines the internal surfaces of the bone (trabeculae, Haversian canals)
- important for bone nutrition and maintenance
Can periosteum and endosteum give rise to cartilage as well as bone?
- yes, they both have osteoblasts
What is woven bone?
- primary, immature bone
- random disposition of collagen fibrils
- usually seen in embryonic development and bone repair
What is lamellar bone?
- secondary, mature bone
- organized collagen in lammellae
- cancellous (spongy) or compact (cortical)
- adult, from remodeling of woven bone
Trabeculae
network of irregular lamellae in spongy (cancellous) bone
What are the spaces of spongy/cancellous bone filled with?
- hematopoietic tissue
Most spongy bone will be converted to _____ except for ______ (3)
- compact bone
- teeth
- short bones
- epiphyses and diaphysis of long bones
anastomosis occurs where in bone?
- with trabeculae trapping blood and lymphatic vessels in canals
Desscribe the early stage of bone formation in spongy bone.
- trabeculae coalesce and trap blood vessels and mesenchymal cells
