MSK Flashcards
Layers of the epidermis
Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Stratum basale
includes claudins and occludins
prevents paracellular movement of solutes
tight junction
calcium-dependent adhesion proteins
cadherins
impaired cartilage proliferation in the growth plate
mutation of FGFR3 (gain of function) -> receptor normally inhibits cartilage proliferation
AD
short extremities with normal sized head (skull) and chest (ribcage) -> intramembranous bone formation not affected (flat bones okay)
mental function, life span & fertility not affected
achondroplasia = dwarfism
bone formation of a cartilage matrix which is replaced by bone
endochondral bone formation
long bones
Congenital defect of bone formation resulting in structurally weak bone
AD
defect in type I collagen synthesis
multiple bone fx (looks like child abuse?)
Blue sclera -> normally contains type I collagen -> blue due to exposure of the choroidal veins
hearing loss (fx of bones of middle ear)
Osteogenesis Imperfecta
Inherited defect of bone resorption (defect in osteoclasts)
thick, heavy bone that fractures easily -> like chalk
due to poor osteoclast function
Bony replacement of marrow causes anemia, thrombocytopenia, leukopenia with extramedullary hematopoiesis
vision impairment -> cranial nerve impingement
hydrocephalus -> narrow foramen magnum
RTA -> mutation in carbonic anhydrase results in decreased resorption of bicarb -> metabolic acidosis
(Note: acidic environment is needed to remove calcium from the bone during resorption)
Osteopetrosis
Tx: bone marrow transplant (osteoclasts are derived from monocytes)
Defective mineralization of osteoid
low levels of Vit D, resulting in low serum calcium & phosphate
child presents with:
pigeon-breast deformity -> pull of resp muscles on rib cage
frontal bossing (enlarged forehead)
bowed legs
Rickets
In adults, it is called Osteomalacia
weak bone with increased risk of fx
Lab: decreased Ca2+, phosphate; increased PTH & ALP
*whenever osteoblasts are active, ALP is elevated -> create an alkaline environment for osteoid to be laid down
reduction in trabecular bone mass
porous bone with increased risk of fx (hip, distal radius, vertebrae)
most common forms: senile & postmenopausal
measure bone loss with DEXA scan
Labs are normal -> excludes osteomalacia
osteoporosis
when does peak bone mass typically occur?
age 30
Imbalance of osteoclast and osteoblast function
late adulthood (age 60 yr)
localized process*
Result: thick sclerotic bone that fractures easily
Bx: mosaic pattern of lamellar bone (osteoblast trying to lay down bone but not in balance)
Increased hat size
bone pain from microfractures
hear loss
lion-like facies
high ALP with normal calcium, phosphate, PTH
Paget Disease
Tx: calcitonin -> inhibits osteoclasts
bisphosphonates -> induce osteoclast apoptosis
complication: osteosarcoma
Infection of marrow and bone, usually in children
hematogenous spread -> seeds metaphysis
most common cause: Staph aureus
Presentation: bone pain, fever, leukocytosis
XR: lytic focus (abscess) aka sequestrum surrounded by sclerosis aka involucrum
osteomyelitis
infection of vertebrae from TB
Pott disease
most commonly fractured bone in the wrist
susceptible to AVN
scaphoid bone (thumb side of the wrist)
femoral head fracture that disrupts blood supply
subcapsular
AVN of ossification centers in children
osteochondrosis
Caused by Legg-Calve-Perthes
lilac discoloration of upper eyelids
scaly erythematous eruptions on knuckles, elbows & knees
muscle weakness: getting up from chair or climbing stairs
B cells & CD4 T cells in muscle
dermatomyositis
If juvenile onset: rash, abdominal pain, calcinosis
CD8 T cells and macrophages around & in muscle symmetric proximal muscle involvement intracellular deposition of amyloid no skin involvement may involve heart, lungs, bvs
polymyositis
immune mediated loss of AChR
female
ptosis and diplopia
thymic hyperplasia -> improvement after thymectomy
myasthenia gravis
seen with small cell carcinoma
muscle weakness that improves with repeated use
Fewer ACh vesicles released with action potential
Does not respond to AChE inhibitors
Lambert-Eaton myasthenic syndrome
decoy receptor made by osteoblasts
short-circuits RANKL
osteoprotegrin (OPG)
missense mutation of fibrillin
fibrillin in microfibrils normally sequesters TGF-beta, so in this case TGF-beta stays activated, causing damage
dislocation of lens
Cardiac risks: MVP & aortic dissection (cystic media necrosis)
marfan syndrome
defect in fibrillar collagen
○ Skin is hyperextensible & joints are hypermobile
○ Predisposition to joint dislocation
○ Skin is stretchable and extremely fragile; vulnerable to trauma. Surgical repair is difficult
○ Internal complications also possibly present: colon rupture, large arteries, ocular fragility, rupture of cornea & retinal detachment, diaphragmatic hernia
Ehlers-Danlos syndrome
Prevents damage to msk system by inhibiting muscle contraction when a muscle exerts too much force
Golgi tendon organs (GTO)
It is a negative feedback system that regulates and maintains muscle tension
