Physiology Of Bone And CT Flashcards
(52 cards)
Key elements of bones
Large amounts of ECM w/ proteins and hydroxyapatite crystals.
Also contain Progenitor cells, osteocytes, blasts and clasts which continue to remodel bone as needed.
- matrix is key provider of strength and stability
Connective tissue cells
Fibroblast, immigrant and resident chondrocytes, macrophages, mast cells and plasma cells.
Pyrophosphate
Inhibits spontaneous hydroxyapatite formation since the concentration of calcium and phosphate ions naturally well exceed the required amount to cause spontaneous formation.
Found in all normal tissues and plasma, except for bone.
% of nutrients bone contains
99% of entire body calcium and phosphate
80% of entire body carbonate
50% of entire body magnesium
35% of entire body sodium
33%/67% ratio of organic:inorganic compounds in bone composition.
Bisphosphonates
Used to combat loss of bone.
Contains high phosphate concentration which promotes hydroxyapatite formation and also encourages osteocytes apoptosis.
Organic 33% of bone consists of what?
28% collagen
5% proteins (non collagen)
67% of inorganic bone composition consists of what?
Primarily hydroxyapatite
What vitamin deficiency causes collagen formation deficiencies?
Vitamin C
Removing organic vs inorganic matrix of bones.
Remove organic = brittle bones (shatter easily)
Remove inorganic = twisty bones (cant resist compression)
Summary of 4 types of bone cells
Progenitor osteocytes: stem cells who differentiate into osteoblasts
Osteoblasts: immature bone cell that secretes osteoid.
Osteoclast: multinucleated cell differentiated from osteoblasts that dissolve hydroxyapatite via acidic molecules
Osteocyte: mature bone cell that maintains bone matrix
RUNX2 gene defects
Defective Gene that inhibits preosteoblast proliferation and differentiation ultimately reducing the total amount of osteoblasts.
- causes lack ossification in teeth and bones, especially the collarbones
(Cleidocranial dysplasia)
Osx (Sp7)gene deficiency
Inhibits osteoblasts and osteocytes maturation and differentiation from preosteoblasts
Secrete poor osteoid that makes mineralization difficult and collagen synthesis poor.
Deficiencies lead to osteogenesis imperfecta (brittle bone disease)
Integrins
Integrins: bind vitronectins on bone surfaces to seal osteoclasts to bone
Vitronectins
Surface proteins that bind to integrins on bone to stabilize osteoclast for bone reabsorption.
Acid proteases and protons
Secreted in the vesicular zone right above the ruffled border of the osteoclast. Are released into the bone and cause break down of hydroxyapatite into Ca2+ and PO4
V-type proton pump and ClC7 channels
Channels and pumps that are located at the ruffled border that help initiate exocytosis of H+ ions and proteases.
Use ATP so is a form of active transport against the proton gradient
Carbonic anhydrase
Supplies the H+ ions in the osteoclast.
Gets protons from water and generates bicarbonate from OH + CO2. Bicarbonate is excreted via Cl-HCO3 pumps
CL-HCO3 exchangers
Antiport that pumps chloride in and bicarbonate out. Helps get chloride into the cell to secrete with protons into the howship lacuna
Clathrin
Mediates formation of secretory vesicles in vesicular zone.
Helps bind the vesicles to the correct area.
Tartrate-resistant Acid phosphatase (TRAP)
Metalloenzyme expressed in osteoclasts and macrophages
Staining of this enzyme is often done to determine osteoclast activity.
Factors that must be expressed for Mesenchymal cells to differentiate into osteoblasts
Cbfa1/Runx2 and Osx
Primary (woven)bone
First bone formed at any site and contains random fiber orientations.
-ultimately replaced by lamellar bone with parallel fibers.
Purposes of bone remodeling
Establish optimum bone strength
Repair damaged bone
Maintain calcium homeostasis
RANKL
receptor activator of KB-nf ligand
Expressed by osteoblasts and helps control osteoclast activity and formation.
