Flashcards in Bone disorders I Deck (18):
bone structure: cortical vs. trabecular
cortical and trabecular bone
cortical bone is dense and non-porous. it provides most of the structural strength of the skeleton
trabecular boneis continuous with the inner surface of cortex. it has a plate and bar structure arranged along lines of stress and strain
more metabolically active portion of bone
bone marrow fills the spaces
diaphysis, metaphysis, and epiphysis ratios of trabecular: cortical bone
diaphysis: mostly cortical
metaphysis: large portion of trabecular bone
epiphysis: growth, articular structure, and subchondral bone
What is in the extracellular matrix of bone
collagen, and calcium hydroxyapatite
From where are osteoblasts dervied?
mesenchymal stem cells
what do osteoblasts do? What receptors do they have? What do they produce?
synthesize organic bone matrix
have estrogen, PTH, and vitamin D receptors
produce OPG (a decoy receptor), RANK ligand, and alkaline phosphatase
What are osteocytes? What do they do? where do they come from? What do they respond to?
they come from osteoblasts encased in matrix
they no longer form bone, though they remain connected to cells on the bone surface
they respond to mechanical signals and influence remodeling. they also stimulate a systemic response
Where to osteoclasts come from? What do they do? What stimulates them? What do they secrete?
come from monocyte precursors
They are stimulated by RANK ligand and M-CSF
the resorb bone at ruffled membrane and secrete protons, lysosomal enzymes, and MMPs (matrix metalloproteins)
What is the RANK/RANK ligand system?
RANK is a receptor on the osteoclast
RANK ligand is a signal on the surface of osteoblasts. Osteoblasts secrete RANK-ligand
OPG is a decoy receptor and an inhibitor of RANK ligand, also secreted by osteoblasts.
This is part of what drives the process of bone remodeling
How does age contribute to osteoporosis?
after age 30, bone turnover usually does not replace the full bone unit
What hormones/minerals are also important in the process of osteoporosis, besides the cells themselves?
calcium, vitamin D, parathyroid hormone, and calcitonin
Calcitonin: who makes it, what does it do
made by thyroid C cells (parafollicular cells)
causes osteoclasts to shrink, inhibits resorption of bone, and causes lose of the ruffled border
also decreases calcium and phosphate resorption in the kidney
What are the two categories of osteoporotic diseases (based on pathogenesis)
osteoclast-mediated bone loss: too much resorption
aka high turnover osteoporosis. primary form that occurs at menopause. High n-telopeptide
osteoblast-mediated bone loss: normal resorption with not enough subsequent bone building
aka low turnover osteoporosis. occurs in elderly and in ppl with underlying genetic collagen disease.
Common fracture sites for a pt with osteoporosis
spine, wrist, and hip
bone mass vs. bone quality in osteoporosis
mass plus distribution = strength
the architecture of the bone matters- distrubtion and balance
structural integrity matters: remodeling rate, and collagen structure
How do you assess for osteoporosis?
Patients who have fragility fractures (fractures from standing height or less)
Or DEXA scans: low dose radiation to look at bone density
may be diagnostic if the pt hasn't had a fracture
may help assess severity if the pt has had a fracture
DEXA loos at hip, spine, and forearm. more negative scores mean more osteoporotic.
Risk factors for osteoporosis independent of bone mass
age, low body weight, personal or parental hx of fragility fracture, smoking, steroids, inflammatory autoimmune disorder (esp. rheumatoid arthritis), high alcohol intake, drugs that cause bone loss
assess risk with the FRAX calculator.
consider treatment in pts with 3% 10 yr risk of hip fracture or 20% risk of major osteoporotic fracture
What lab tests should you do for osteoporosis? What do you look for? In which patients is this particularly important?
always look for secondary causes of osteoporosis- esp. in premenopausal women and men with osteoporosis
look for low vitamin D levels
consider calcium and vitamin D levels, look for 1,25 vitamin D (activated vitamin D) if the pt has kidney failure
look at peak testosterone levels in men
consider evaluation for multiple myeloma