Bone Flashcards
What is bone tissue
-specialized CT with mineralized matrix and cells ( osteoblasts, osteoclasts and osteocytes )
Functions of Osseous tissue
- provide solid framework for the body
- provide attachments for muscle and tendons
- converts skeleto-muscular energy into movement
- protects vital organs
- calcium reservoir
- blood formation occurs in bone marrow
Osteoblasts origin
-mesenchymal stem cells from the mesoderm
Osteoblasts function, type of secretion and where found
- synthesize and secrete matrix vesicles
- secrete calcium hydroxyapatite to calcify matrix
- proteoglycans ( osteonectin - bind cells to ecm )
- collagen 2
-found at surface of bone matrix
Shape of osteoblasts and how they connect to each other
- cubodial
- adherent and gap junctions
What happens to osteoblasts as they mature
- die by apoptosis ( major pathway )
- differentiate into osteocytes
- flatten and become bone lining cells
Lacunae and canaliculi
- cavities in matrix in which osteocytes are trapped
- dendritic like extensions of osteocytes and which extend into matrix
How does bone mineralization occur
- after Osteoid has been secreted
- osteoblasts secrete vitamin k dependent osteocalcin which binds to Ca2+ ions and increase conc of mineral locally
- also secrete matrix vesicles rich in alkaline phosphate and enzymes
- the enzymes hydrolyze phosphate from macromolecules and increase conc locally
- the matrix vesicles serve as foci for crystal formation which grow and more minerals are secreted and embedd collagen in it forming matrix
Osteocytes how they form and function
-by osteoblasts surround by matrix they secrete
- maintain matrix
- serve as detectors of stress and cracks in bone
- trigger remedial functions in other cells
Function of canaliculi
- exchange of metabolites from vessels hi each other and matrix
- communication through gap junctions attaching canaliculi
Osteoclasts how they form and structure
- osteoblasts and other bone marrow cells secrete RANK Ligand which binds to rank receptors on monocytes
- this induces a signaling cascade stimulating the precursor to fuse together
-large motile and multi nucleated
Function of osteoclasts
Bone resorption during remodeling or to release Ca2+ into blood stream
Howship / resorption lacunae
-enzyme etched depressions occupied by osteoclasts during bone resorption
What is bone remodeling and function
-replaced of bone through resorption with new bone
- remove brittle old bone
- repairs micro cracks
- repairs fractures
What is resorption
-when inorganic matter of bone is dimineralized and organic part is degraded
What is a characteristics of osteoclasts
-the enzyme TRAP tartrate resistant acid phosphatase
Origin of osteoclasts and they precursor
Hematopoietic in origin
-precursor is monocyte
What hormones control osteoclasts formation
- vitamin D3
- parathyroid
- cytokines ( IL-1 , IL-6 )
How do osteoclasts prepare for resorption
Describe bone respiratory
- osteoclasts at ruffled border attach to membrane using proteins forming resorption compartment
- pumps protons from H2CO3 into inorganic matrix to demineralize it forming howship lacunae and exposes organic part
- organic part degraded by enzymes and vesicles phagocytosis then endocytized
Effect of bone resorption
Ca2+ released into blood steam
-old bone degraded
Proteins which attach to membrane from osteoclasts
Osteopontin
-bone sialoprotein BSP
What is sealing zone and use
- area between osteoclasts and matrix
- produces conducive micro environment for resorption
Enzymes which degrade organic part of bone
Acid phosphatase
-cathepsin K
Hormones which affect bone resorption and where they come from
- RANKL helps osteoclasts form and mature
- osteoprotegerin from osteoblasts bind with RANKL and inhibit osteoclasts formation
- parathyroid from parathyroid gland responses to low Ca in blood and directly stimulates osteoblasts to make RANKL
- calcitonin from parafollicular cells inhibit bone resorption
Wolffs Law
-bone that bear high mechanical weight resorp at a high rate
Effect of vitamin D on resorption
-aids in intestinal digestion of calcium leading to high levels of calcitonin and low levels of parathyroid thus inhibited resorption.
Components of bone matrix and their proportions
- 50% dry weight is calcified bone
- ions such as Ca and Mg
- organic matter is 90% collagen
- glycoproteins ( osteonectin )
- proteoglycans
Surface of hydroxyapatite is hydrate
So !?
-facilitates exchange between the mineral and bodily fluids
Periosteum structure and function
- outer fibrous dense layer of CT with collagen 1 and blood vessels
- inner cellular later with mesenchymal CT and osteoblasts
- supply blood vessels to bone
- protective layer
What are sharpey fibers
-bundles of periosteum collagen which penetrate matrix and bind peri to matrix
Endosteal function and structure
-cover trabeculae In spongy bone
-has cells ( progenitor, osteoclasts , )
And sparse Delicate network of collagen
Woven bone structure and where found
-irregular arrangement of cells and matrix that intertwines
- found in fracture as hard callus
- in developing bones
Woven bone characteristics
- low mineral content
- low density and can’t bear much mechanical stress
- high conc of osteocytes
Other name for woven
Primary bone
Immature bone
Which bone developed the quickest
Woven
Lamellae bone structure , characteristics , where found and synonyms
-parallel layer of thin sheets of collagen and matrix
- heavily calcified
- regularly spaced cells
- found in all adult bones
- mature bone
- secondary bone
Types of lamellae, description, where found and function
1 interstitial bone - parallel groups of lamellae in between osteons. Made of leftover osteons from respiration
2 circumferential lamellae - external and internal found beneath periosteum and cancellous bone. Strengthens Cortical bone with osteons
3 concentric lamellae - parallel sheats of lamellae forming concentric circles and protecting Haversian canals
What is an osteon
-cylindrical tube parallel to long axis of diaphysis with concentric lamellae each and a Haversian canal in the middle
What is Haversian canal
-narrow tube between concentric lamellae with blood vessels and nerves
What is in between lamellae
-lacunae
Cement line
-outer boundary layer of a osteon
How are osteons formed
-by laying of matrix around pre existing blood vessels
Volkmanns canal structure and use
-transverse canals that connect Haversian canals together and to blood vessels of the periosteum
What is replaced in cortical bone during remodeling
-osteon
Describe bone remodeling
- osteoclasts tunnel a core through bone resorbing existing bone
- tunnel invaded by capillaries and progenitor which diff into osteoblasts secrete osteoid in a cyclic manner which then calcifies forming concentric lamellae
What happens to trapped osteoblasts during resorption
-diff into osteocytes
Cancellous bone description, structure and function
- found in the middle of bone
- has spicules known as trabeculae in which intertwine and are covered by endosteal
- filled with bone marrow where blood is made
- 20% of bone
- less dense
- spongy consistency
Cortical bone description, structure and function
- found at the peripheral of bones - underneath periosteum
- 80% mass of bone
- has osteons and parallel lamellae
