Bone Flashcards
What is cortical/compact/lamellar bone?
• Diaphysis of long bones (such as tibia and femur)
• arranged in Haversian systems ->series of concentric lamellae of collagen fibres surrounding a central canal with blood vessels.
• Nutrients - > central parts of the bone ->interconnecting system of canaliculi that run between osteocytes buried deep within bone matrix and lining cells on the bone surfa
What is medullary bone/trabecular/spongy bone
• vertebral bodies and the ends of the long bones
• trabecular bone has a similar structure, but here the lamellae run parallel to the bone surface, rather than concentrically as in cortical bone
What are the cellular components of bone?
• Osteoblasts - surface of the osteoid matrix synthesize, transport, and assemble matrix and regulate mineralization. Quiescent osteoblasts -remain on the trabecular surface or become
embedded within the matrix as osteocytes. Blasts=builders
• Osteocytes are interconnected - network of dendritic cytoplasmic processes through tunnels (canaliculi) within the matrix. Osteocytes help control calcium and phosphate levels in the microenvironment, detect mechanical forces - translate those forces into biologic activity— mechanotransduction.
• Osteoclasts are specialized multinucleated macrophages that are derived from circulating monocytes and resorb bone. Surface integrin proteins allow osteoclasts to attach to the matrix ->
sealed extracellular trench (resorption pit). Secretion of acid and neutral proteases, predominantly matrix metalloproteases (MMPs) ->dissolution of inorganic and organic bone
components. Clasts=claw away bones
What pathways increase vs decrease osteoclastic differentiation?
• Pathways increased osteoclastic differentiation-RANK (Receptor
activator of nuclear factor 𝜅𝜅 B) ligand and RANK ligand receptor. M-
CSF regulated by PTH
• Pathways to reduce osteoclast differentiation -WNT signaling –
stimulate osteoblasts to osteoprotegrin (OPG) synthesis
What is the process of bone remodelling?
What are the roles of PTH and calcitriol?
• PTH is the major regulator; receptors on osteoblasts, none on osteoclasts. Intermittent PTH -Stimulates osteoblast activity and bone formation.
• Sustained high levels of PTH for a longer time cause a shift in the balance of cell
activity, favouring osteoclast activity and bone resorption. PTH -> osteoblasts ->RANKL rather than acting directly on osteoclast cells.
• Calcitriol (1,25-dihydroxycholecalciferol) also stimulates bone resorption by upregulating RANKL expression in osteocytes
What is the role of sex steroids?
• Oestrogens promote osteoblast function and stimulate apoptosis of osteoclasts, thereby promoting bone formation. Promote calcium
uptake in the gut.
• Androgens are also anabolic in bone -> local conversion to oestrogens.
• Glucocorticoids -> catabolic in bone ->promote osteoclast activity, inhibit calcium uptake in the gut. Long term glucocorticoid therapy –risk of osteoporosis
How is osteoporosis diagnosed?
• Dual energy X-ray absorptiometry scanning (DEXA scan)
T-score – compares to peak bone mass of an average 30 year old female
(standard deviations)
• +1 to -1 - bone density is in the normal range for a young and healthy person.
• -1 to -2.5 - bone density is slightly below the normal range for a young and
healthy person, also known as osteopenia.
• -2.5 and below - bone density is in the osteoporosis range.
Z-score
Compares bone density to people of the same age as the individua
What are the types of fracture?
What is the process of fracture healing?
What are the short vs long term complications of fractures?
What is compartment syndrome?
What is a fat embolism?
What are the benign bone forming tumours?
What is an osteosarcoma?
• most common primary malignant tumor of bone
• Bimodal -75% occurring before 20 years of age, smaller peak occurs in older
adults (predisposing conditions -Paget disease, bone infarcts, and prior radiation,
sometimes called secondary osteosarcomas).
• Men>women - 1.6:1
• Tumors usually arise in the metaphyseal region of the long bones; almost 50% are
near the knee in the distal femur or proximal tibia.
• Symptoms – bone pain, pathological fra
