Bone Physiology Flashcards
What is the epiphysis
Head
Articular surface
What is the diaphysis
Shaft
What is the metaphysis
Growth plate
What are 3 examples of flat bones
Skull, ribs and sternum
What are the 4 bone types
Sesamoid
Short
Irregular
Alveolar bone of the jaw
What is intramembranous formation
Bone forms directly from mesenchymal cells
What is endochondral ossification
Bone forms from a cartilaginous template
Morphogenesis and growth phases
What happens during intramembranous formation
Mesenchymal condensations form early in embryogenesis
Differentiate into osteoblasts form osteoid which mineralises
How is intramembranous formation genetically regulated
By patterning genes encoding transcription factors such as homeobox (HOX) or paired box (PAX)
What is the first stage of endochondral ossification
Mesenchymal cells form condensations (lateral plate mesoderm)
What is the second stage of endochondral ossification
Differentiate into chondrocytes and begin to proliferate and secrete cartilaginous matrix
What is the third stage of endochondral ossification
Chondrocytes differentiate into hypertrophic chondrocytes
What is the last stage of endochondral ossification
Blood vessels invade cartilaginous matrix. Surrounding perichondrial cells differentiate into osteoblasts forming the primary ossification centre
What is the secondary ossification of endochondral ossification
Appear in the epiphyses forming the articular surfaces of the bone
What are the 5 zones of the growth plate
Resting zone
Proliferative zone
Pre hypertrophic zone
Hypertrophic zone
Invasion zone
How are chondrocytes arranged in the growth plate
In columns
How is proliferation and differentiation in growth plate
Are tightly regulated
Which type of bone is the main site of calcium exchange
Trabecular, spongy, cancellous
What are 3 types of cells in bone marrow
Erythrocytes
Lymphocytes
Cells of the myeloid lineage
What do bone lining cells detect
Changes in loading environment and expose bone surface for resorption
What is the main mechano sensitive bone cell
Osteocytes
What is osteoblastic lineage
Stromal precursors that are capable of forming either osteoblasts or adipose cells
What is osteoclastic lineage
Myeloid
What are 4 physiological factors that impact on bone homeostasis
Fluctuations in serum calcium
Changes in mechanical loading
Repair of micro fractures
Hormonal status
What are the 5 stages of bone formation and resorption
Resting bone surface
Resorption
Reversal
Bone formation
Mineralisation
What do osteoblasts synthesise
The organic matrix of bone (osteoid) and control its mineralisation
After finishing making new bone what 3 cells can osteoblasts differentiate into
Osteocytes
Bone lining cells
Undergo apoptosis
What do osteoclasts form from
Pluripotent CD34+ mononuclear phagocytes precursors that can form many myeloid cell types
What 2 physiological regulators are osteoclast differentiation and bone resorption
Low serum Ca2+ levels (calcium homeostasis)
Decreases in mechanical loading
What 3 pathological regulators of osteoclasts
Disruption of steroid hormone levels
Inflammation
Cancer
What does RANKL bind to
It’s receptor RANK on osteoclast precursors
What does osteoblastic osteoprotegerin (OPG) do
Further layer of control which is a soluble decoy receptor for RANKL
What is the first process of bone resorption
Attaches to surface through a5 b3 integrin interaction with RGD containing proteins
What is the second process of bone resorption
Polarisation of osteoclast formation of ruffled border, actin ring and sealed zone
What is the third process of bone resorption
Acidification of the sealed zone by active transport of H+ to breakdown mineral component of bone. Oc pH maintained by Cl-/HCO3- exchanger on basolateral surface
What is the fourth process of bone resorption
Release of cathepsin K and other proteases that digest collagen
What is the fifth process of bone resorption
Creates a resorption pit 4-5uM deep
