Flashcards in Bone Deck (40)
When does resorption begin to exceed remodeling?
4th decade (10% of bone remodeled annually)
What are the two types of bone?
cortical or compact and trabecular or cancellous/spongy
Where is cortical/compact bone found?
80% of skeletal mass and provides structural support
Where is cancellous/spongy bone found?
the remaining 20% and forming interconnecting plates covered in osteoblasts while provide a place for trilineage hematopoiesis
What are the differences between lamellar bone and woven bone (microscopic terms)?
lamellar bone is essentially remodeled compact bone comprised of osteons (haversian systems) that run longitudinally and are very organized and stress-oriented and less flexible. Woven bone is essentially immature bone that is not stress oriented and has higher osteocytes per unit volume and can mature to lamellar bone.
What are the main components of bone?
-type I collagen (aka osteoid)
What is the role of osteoblasts?
they are derived from marrow stroma and lay down bone matrix or osteoid (90% type 1 collagen) and then mineralize it with hydroxyapatite crystals to form lamellar bone
What does bone mineralization require?
What receptors do osteoblasts have?
PTH and Vit D3
How do osteoclasts resorb bone?
using proteases to degrade the collagen dan cdi to dissolve the mineral
The 'pits' created by osteoclasts are called ______
What are osteoclasts derived from?
same stem cells as macrophages
What drives differentiation of osteoclasts?
binding of M-CSF and RANKL on stroma cells/osteoblasts to receptors on osteoclast precursors promotes differentiation via NF-kB action in the nucleus
What prevents binding of RANKL on osteoBLASTS to RANK receptors on osteoclast precursors, thus blocking their differentiation?
osteroprotegerin, aka OPG-a soluble protein (binds to RANKL on osteroblasts)
What happens in hyperparathyroidism?
PTH will stimulate osteoblasts and increase alk phosphatase, and thus osteoblast expression of RANKL which increased osteoclast differentiation and activity
What is osteogenesis imperfecta?
aka brittle bone disease, disease group caused by defective synthesis of a1 or a2 chains of type 1 collagen
Why might there be involvement of skin, joints, teeth, and eyes (and others) in OI?
because type 1 collagen is a vital component of extracellular matrix in other parts of the body
Describe Type 1 OI.
children present with a modestly increased proclivity for fractures (decreases after puberty), classic blue sclera due to increased transparency of the sclera, hearing loss, but have an overall normal lifespan
Why is hearing loss associated with type 1 OI
might be related to conduction defects in the middle and inner ear bones
How is the mouth affected by Type 1 OI?
small misshapen teeth as a result of dentin deficiency
Describe Type 2 OI.
fatal in utero or immediately postpartum as a consequence of multiple fractures that occur before birth
What is the most common cause of dwarfism?
What causes acondroplasia and thanatophoric dwarfism?
an activating point mutation in fibroblast growth factor receptor 3 (FGFR3)
What is the affect of mutation in FGFR3?
FGFR3 typically inhibits cartilage proliferation, in disease FGFR3 is turned on constantly, suppressing cartilage growth
MOI of acondroplasia and thanatophoric dwarfism?
AD or new spontaneous mutations (80%)
What is Thanatophoric (death-loving) dwarfism?
a lethal variant of dwarfism with a small thorax leading to respiratory complications and death
Acondroplasia affects all bones that develop how?
via enchondral ossification
How does acondroplasia present?
disproportionate shortening of the proximal extremities, bowing of legs, and frontal bossing with mid face hypoplasia
can see 'trident' hands with short fingers
T or F. Acondroplasia affects intelligence or lifespan
What genotype is not compatible with life?
have to have two copies of mutated FGFR3
What is osteopetrosis?
decreased bone resorption (poor osteoclast function) leading to dense, solid, and stone-like bones that over time weaken and fracture like a piece of CHALK
What causes osteopetrosis?
carbonic anhydrase II deficiency leads to loss of the acidic micro-environment needed for bone resorption.
NOTE: CA2 is required by osteoclasts and renal tubular cells to generate protons from CO2 and H2O. Its absence prevents osteoclasts from acidifying the resorption pit and solubilizing hydroxyapatite, and also blocks acidification of urine by the renal tubular cells
How does osteopetrosis present?
-erlenmeyer flask shaped deformity
-vision and hearing impairment
-hydrocephalus- narrowing of foramen magnum
-renal tubular acidosis
What causes the erlenmeyer flask shaped deformity seen in osteopetrosis?
lack of trabecular bone formation
Why is pancytopenia a symptom of osteopetrosis?
bone marrow doesn't form properly
Why is RTA a symptom of osteopetrosis?
lack of CAII leads to lack of HCO3- resorption
Treatment for osteopetrosis?
stem cell transplant
What causes rickets?
defects in matrix mineralization due to vitD disturbance (deficiency, abnormal metabolism or calcium deficiency) causes an increased accumulation of unmineralized bone matrix
What are some common causes of vitD deficiency?
-lack of sunlight