Metabolic Disease Flashcards
What is the epiphysis?
The end of a long bone that is composed of cancellous bone and thin cortical bone
What is the diaphysis?
Center or shaft of long bone that consists of the medullary (marrow) cavity with less cancellous bone and a thick cortex
What is the metaphysis?
A transition zone between diaphysis and epiphysis that is composed primarily of cancellous bone
What is the physis?
It is the epiphyseal growth plate in skeletally immature and consists of the epiphysis and metaphysis
What is articular cartilage?
Hyaline cartilage covering cortical joint surfaces of epiphysis
What is periosteum?
Specialized connective fibrous tissue with osteogenic potential that covers bone but is absent in joint spaces and at attachment sites of tendons or ligaments
What is endosteum?
Inner lining of diaphysis and of cancellous bone, has osteogenic potential
What is enthesis?
Fibrous or fibrocartilaginous insertion of a tendon or ligament to bone
What is osteoid?
Unmineralized immature, rapidly formed, but poorly organized bone matrix (organic matrix + collagen type I) with high numbers of active osteoblasts
What is woven bone?
Mineralized immature, formed rapidly, but poorly organized bone matrix with a high number of active osteoblasts
What is the star?
Osteoid
What is the arrow?
Woven bone
What is lamellar bone?
Mineralized mature bone that is formed slowly from collagen type I arranged in parallel fibers in response to mechanical stress
What are the two subtypes of lamellar bone?
1) cortical/compact bone: longitudinal, circumferential, and concentric collagen type I lamella formed by constant remodeling in response to mechanical stress
2) cancellous/spongy bone: formed by enchondral ossification, lamella of collagen type I aligned longitudinally in response to mechanical stress
What type of bone is this?
Lamellar bone
What does bone matrix consist of?
Inorganics: calcium phosphate mostly
Organic matrix: mostly type I collagen and growth factors
What are osteoblasts?
Cells of bone that are derived from mesenchymal stem cells under influence of growth factors
What is the function of osteoblasts?
1) produce matrix proteins and initiate mineralization
2) has cell surface receptors for PTH, insulin-like growth factor-1, vitamin D, and estrogen receptors
What are osteocytes?
They are bone cells that are derived from osteoblasts and incorporated into bone. They are the most common bone-formingcell and they communicate through canaliculi within osteon units.
What is the function of osteocytes?
1) important in regulating Ca2+ and PO4-
2) mechanicalforces cause transcriptional activation of cAMP pathways within osteocytes resulting in remodeling of bone
What are osteoclasts?
Bone marrow derived monocyte lineage. Progenitor cells with RANK receptors upregulate osteoclast-related genes when RANK-L bindstoreceptor.
What does osteoprotegrin do?
It is produced by osteoblasts to block RANK:RANK-L interactions and prevent osteoclast activation.
What do osteoclasts do?
1) responsible for bone resorption (undoes the work of osteoblasts)
2) bind to bone and form “resorption pits” (Howship lacunae) where they acidify extracellular space to release minerals and secrete digestive enzymes to dissolve organic matrix and also release growth factors/cytokines to stimulate osteoblasts to balance bone formation and destruction
What is the resting zone in a growthplate?
First zone with inactive chondrocytes
What is a zone of proliferation in a growth plate?
Chondrocytes proliferate and secrete cartilaginous matrices
What is the zone of hypertrophy in a growth plate?
Chondrocytes enlarge, form columns, and secrete cartilaginous matrix
What is the zone of provisional calcification in the growth plate?
A zone where vitamin D causes calcificationof the cartilaginous matrix and entrapped chondrocytes undergo apoptosis
What are primary trabeculae in growth plates?
Scaffolds of dead cartilage that form the framework on which osteoprogenitor cells deposit bone matrix
Which factors stimulate cartilage growth?
IHH, PTHrP, BMP
Which factors inhibit cartilage growth?
FGF
What causes osteogenesis imperfecta?
Deficiency in synthesis of type I collagen (can be partial decrease in protein synthesis or a more significant loss)
What are the symptoms of osteogenesis imperfecta?
- Fragile bones that are frequently fractured (and heal with excess callus)
- Joint laxity + secondary osteoarthritis
- Blue sclera in eyes
- Hearing defects
- Dentinogenesis imperfecta in teeth
What is osteoporosis?
A disease caused by local or generalized low bone mass, characterized by microarchitectural deterioration and increased bone fragility
What are the causes of osteoporosis?
- genetic and environmental
- bone density/mass peaks in early adulthood and declines with age
What is postmenopausal osteoporosis?
Osteoporosis following menopause and estrogen deficiency, which results in up-regulation of IL-1, IL-6, TNF-alpha, and downregulation of OPG. It affects cancellous bone more than cortical bone, so it affects bones with high surface area (ex. vertebral body).
What fractures are most common in postmenopausal osteoporosis?
Vertebral and wrist fractures because it targets high-surface area cancellous bone
What type of osteoporosis is considered high-turnover?
Postmenopausal osteoporosis
What is senile osteoporosis?
It affects men and women > 70 years of age. Osteoblasts become less potent with age, which affects mostly the cortex of bone.
What type of fractures are most common in senile osteoporosis?
Hip and vertebral fractures due to effects on bone cortex
What type of osteoporosis is considered low-turnover osteoporosis?
Senile osteoporosis
What does turnover mean in osteoporosis?
It refers to whether osteoblasts are active to compensate for bone loss from osteoclasts. They are active in postmenopausal osteoporosis and are not active in senile osteoporosis.
What is are mucopolysaccharidoses?
Closely related diseases caused by mutations in lysosomal enzymes that degrade GAGs leading to accumulation of GAGs in cells, which induces cellular damage. In bone, loss of chondrocytes and osteoblasts leads to decreased bone formation.
What are clinical signs of mucopolysaccharidoses?
Cardiac valve disease, mental retardation, hepatosplenomegaly, corneal clouding, umbilical/inguinal hernia, coarse facies, macroglossia
What cells in bone and soft tissue are affected in mucopolysaccharidoses?
Fibroblasts, chondrocytes, osteoblasts, and osteoclasts
What are bone/soft tissue symptoms of mucopolysaccharideoses?
- defects in endochondral ossification lead to short stature, kyphosis/scoliosis, and hypoplastic teeth
- abnormal intramembranous ossification leads to macrocephaly, abnormal bone remodeling, and osteoporosis
- accumulation of GAG in tendons/ligaments induces inflammation that leads to joint stiffness and/or hypermobility
What is rickets/osteomalacia?
A disease where vitamin D deficiency results in 1) the inability to calcify the zone of hypertrophy in developing growth plates and 2) the inability to calcify osteoid formed throughout life duringremodelin
What is the difference between rickets and osteomalacia?
Rickets occurs before the physis closes (aka in childhood), whereas osteomalacia occurs after the physis closes
What is hyperparathyroidism?
A disease where abnormally high PTH stimulates osteoclast activity and affects cortical bone more than cancellous bon
What are the clinical findings of hyperparathyroidism?
GI moans, bones, renal stones, and psychiactric overtones
What are the microscopic findings of hyperparathyroidism?
Cortical aggregates of activated osteoclasts that form “cutting cones” and enlarged Haversian canals, dissecting osteoclasts through cancellous bone, and cortical thinning
What are the long-term effects of untreated hyperparathyroidism?
Microfractures in bones that cause bleeding, hemosiderin deposition, and reactive bone marrow fibrosis (also called brown tumor of bone)
What is paget disease of bone?
Collage of matrix madness due to dyssynchrony between osteoclasts and osteoblasts that mostly affects adults of European ancestry and mostly affects multiple bones at once.
What are the phases of paget disease of bone?
Initially there is marked bone resorption, followed by a mixed lytic and blastic stage, culminating in a sclerotic phase with thickened bone exhibiting a haphazard arrangement of cement lines
What is the etiology of Paget disease of bone?
A combination of a genetic mutation in p62, a regulator of RANK-L/Nuclear factor mediated osteoclastogeneisis coupled with paramyxovirus infection
What are the clinical effects of paget disease of bone?
Chalk-stick fractures, cranial nerve defects, cardiac failure, and sarcoma
What is osteopetrosis?
A disease caused by absent or defective osteoclast activity such that they cannot properly remodel bone. The medullary canal fills with bone and calcified cartilage instead of hematopoetic elements resulting in anemia, cranial nerve defects, hearing loss, and fractures.
Microscopically, lamellar bone differs from woven bone by:
a) having a greater number of osteocytes and osteoblasts
b) the longitudinal, concentric, and circumferential patternof collagen deposition in lamellar bone
c) presence of calcium in lamellar bone
d) its rapid formation in contrast to the slow deposition of woven bone
e) absence of Haversian canals in lamellar bone
b) the longitudinal, concentric, and circumferential patternof collagen deposition in lamellar bone
The fragile balance between osteoclasts and osteoblasts is significantly altered in which condition:
a) osteogenesis imperfecta
b) osteosarcoma
c) osteomyelitis
d) osteoid osteoma
e) Paget’s disease
e) Paget’s disease
Postmenopausal osteoporosis:
a) has the exact same pathogensis as senile osteoporosis
b) has a greater effect on cortical bone
c) estrogen deficiency results in increased osteoblastic activity
d) enhanced osteoclastic activity is the major cause
e) considered a low turnover subtype of osteoporosis
d) enhanced osteoclastic activity is the major cause
Ricketts is caused by a defect that affects which zone in the growth plate?
a) resting zone
b) zone of proliferation
c) zone of hypertrophy
d) zone of provisional calcification
d) zone of provisional calcification
