Bone L1

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What is the fundamental characteristic of bone and what other roles does it play in the body?	Bone is known for its persistence after death and vitality during life. Other roles include: mineral homeostasis; houses hematopoietic elements; provides mechanical support; protects internal organs and determines body size &shape.
What are the 5 different bone types? (Give an example of each)	1) Long bone (humerus). 2) Flat Bone (sternum). 3) Short bone (carpal of wrist). 4) Irregular bone (vertebra). 5) Sesamoid bone (patella)
What are bones composed of?	Minerals (50-70%), an organic matrix (20-40%), water (5-10%) and lipids (about 3%)
What is the organic matrix composed of? What are its properties?	It is composed of 90% collagen and 10% other proteins. It is known for its elasticity and flexibility.
What is the main mineral of bone?	Hydroxyapatite (calcium phosphate)
What is new, un-mineralised bone called? What is its common characteristics?	Osteoid. It is strong, stable and hard.
Name 3 determent's of bone strength.	Bone mass (mostly), matrix composition and micro-architecture of bone.
What are osteoprogenitor cells and what do they do?	They are pluripotent, mesenchymal stem cells found on bone surfaces. They are stimulated by growth factors to produce offspring that differentiate into osteoblasts.
What are osteoblasts and what is their main job?	They are derived from bone marrow stromal cells and are located on the bone surface. They synthesize, transport and arrange proteins of bone matrix.
What other jobs do osteoblasts do?	They initiate mineralization, via alkaline phosphatases, AND they possess receptors that kind regulatory hormones, cytokines, GFs and matrix proteins.
What is the difference between osteoblasts, osteocytes and bone lining cells?	Osteoblasts are later surrounded by new organic matrix after which they become osteocytes. If they remain on the bone surface and become flattened and dormant, they are then known as bone lining cells.
What are osteocytes and what do they do?	Osteocytes are found in bone matrix in pits called lacunae. They communicate with each other and surface cells via canaliculi. They control calcium and phosphate levels in the micro-environment and also detect mechanical forces and translate them (mechanotransduction)
What are osteoclasts and what do they do?	Osteoclasts are cells derived from hematopoietic cells and are responsible for bone resorption. They are regulated by cytokines and growth factors. They only live for about 2 weeks.
How does bone resorption work?	Osteoclasts bine to bone surface via integrins and form an underlying resorption pit. The osteoclast membrane facing the pit forms a ruffled border to increase SA. A proton pump creates an acidic environment whilst proteases break down organic material.
How is bone resorption limited to one area?	Adjacent cells form a tight seal with the bone surface to prevent leakage from the osteoclast and it's resorption pit.
What is the proper term for compact bone?	Cortical Bone
What is cortical bone and where is it found?	Cortical bone is the tissue found on the outer layer of all bones (interior of long bones too!) and makes up about 80% of total bone mass. It is a dense tissue of one mineral and extracellular matrix elements (blood vessels, osteocytes). It provides strength for weight bearing (long bones).
What is osteocytic osteolysis?	It is the transfer of calcium from inside of the bone to the surface via canaliculi.
What is the more formal term for spongy bone?	Trabecular Bone
What is trabecular bone and where is it found	It is a type of tissue found in the interior of bones. It is made up of in spicules that extend from the cortex into the medullary cavity. These spicules are lined with osteoblasts and osteoclasts which constantly synthesise and resorb bone.
What 'disease' occurs when the rate of bone resorption exceeds the rate of bone synthesis over a fair period of time?	Osteoporosis
What is the protein matrix of bone composed of?	Collagen and matrix proteins.
Name the 3 main types of osteoblast-derived proteins are found in the extracellular matrix?	Type 1 collagen, Osteocalcin and Osteonectin.
What is important to know about type 1 collagen?	Cross-linking occurs between collagen firers to create strength. It is highly organised in its arrangement. Collagen provides sites for nucleation of hydroxyapatite crystals (mineral component).
How is collagen laid down in bone formation?	Osteoblasts deposit collagen as woven bone during rapid bone formation (fetal skeleton, quick and resistant, in children) OR as orderly lamellar bone (deposited slowly and is stronger, gradually replaces woven bone during growth).
What is osteocalcin and where is it found?	Osteocalcin binds calcium to hydroxyapatite. It is generally found at the site of new bone formation and is induced (to synthesise) by vitamin D. It is unique to bone (marker of osteoblast activity).
What is osteonectin and where is it found?	Osteonectin helps the mineralization of collagen fibers and binds collagen fibres to hydroxyapatite.
Signalling pathways allow bone cells and locally produced factors to regulate homeostasis. What are the 3 pathways?	The RANK ligand pathway, the M-CSF pathway and the WNT/beta-catenin pathway.
What does the RANK ligand pathway do?	It stimulates the differentiated of pre-osteoclasts into mature osteoclasts using a ligand, receptor and OPG (Osteoprotegrin).
How does the RANKL pathway work?	The binding of RANK ligand (on stromal cell/osteoblast) to the RANK receptor (on pre-osteoclast) stimulates NF-KB activation and thus differentiation into a mature osteoclast. OPG secreted by osteoblasts acts as a decoy receptor (protects bone from osteoclastic activity).
How does the M-CSF (Macrophage Colony Stimulating Factor) pathway work?	This factor is produced by osteoblasts. It attaches to a M-CSF receptor on pre-osteoclasts and assists in differentiation by stimulating tyrosine kinase activity.
What does the WNT/beta-catenin pathway do?	WNT proteins produced by marrow stromal cells bind to LRP5/6 receptors on osteoblasts. This binding stimulates beta-catenin to produce OPG production.
Osteoblasts can enhance/inhibit osteoclast development and function by expressing OPG and RANKL at different levels. What factors effect this expression?	Hormones, vitamin D, inflammatory cytokines and growth factors... (influence signalling)

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	Erstellt von Melissa Thomas vor fast 5 Jahre