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MSK-Derm by Minnie > SM 233a - Metabolic Disease > Flashcards

SM 233a - Metabolic Disease Flashcards

1
Q

What is zone 5?

Which diseases affect this zone?

A

Primary trabeculae

  • Osteogenesis imperfecta
  • Scurvy
  • Osteopetrosis
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2
Q

Which zone of enchondral bone formation is affected by osteogenesis imperfecta?

A

Zone 5 - Formation of primary bone trabeculae

Osteogenesis imperfecta = inabilty to lay down type I collagen

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3
Q

Which bones are most affected by postmenopausal osteoporosis?

A

Bones with large surface area

Vertebral body, wrist

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4
Q

Which bone disorder is characterized by “absent or defective osteoclast activity”

A

Osteopetrosis

Usually due to a mutation in the H+ ATPase

  • Cannot acidify the osteoclast resorption pit -> remodelling cannot occur
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5
Q

Which process of bone formation is responsible for pre-pubertal bone lengthening?

Which process of bone formation is responsible for pre-pubertal thickening of the cortex and bone widening?

A

Lengthening = endchondral ossification

Thickening/widening = intramembranous ossification

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6
Q

Which bone cells produce type I collagen?

A

Osteoblasts

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7
Q

What are the two types of immature bone?

A

Osteoid (unmineralized)

Woven bone (mineralized, but not yet mature)

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8
Q

What are the mucopolysaccharidoses?

A

Closely related diseases caused by mutations in lysosomal enzymes that degrade glycosaminoglycans (GAGs)

  • Accumulation of GAGs and cellular damage
  • May present as:
    • Cardiac valvular disease
    • Mental retardation
    • Hepatosplenomegaly
    • Corneal clouding
    • Umbilical/inquinal hernia
    • Coarse facies & macroglossia
    • Enlarged gingiva
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9
Q

Describe the inheritance of the mucopolysaccharidoses

A

Autosomal recessive

(Except Hunter syndrome, which is x-linked recessive)

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10
Q

What are the most common cells within bone?

A

Osteocytes

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11
Q

What kind of bone contains Haversian systems?

A

Cortical bone

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12
Q

Which disease is characterized by widening of growth plates due to cartilage accumulation?

A

Rickets in children

  • Cartilage accumulates because it cannot be calcified to from woven (immature) bone
  • Caused by vitamin D deficiency

(In adults, inability to calcify organic bone matrix is called osteomalacia, also caused by vitamin D deficiency)

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13
Q

Describe the pathogenesis of hyperparathyroidism

  • Primary:
  • Secondary:
A
  • Primary:
    • Increased PTH secretion
    • Usually result of parathyroid adenoma
  • Secondary:
    • Usually results from chronic renal failure
      • Cannot resorb Ca2+
      • Chronically low serum Ca2+ = constant signal for PTH release
    • Results in parathyroid hyperplasia
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14
Q

What is zone 2?

Which diseases affect this zone?

A

Zone of proliferation

  • Achondroplasia
  • Mucopolysaccharidosis
    • Hunter and hurler syndromes
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15
Q

Which bone disease results from mutated p62?

A

Paget’s disease of bone

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16
Q

What bone disease is caused by mutations in H+ ATPase?

A

Osteopetrosis

  • Inability to acidify the osteoclast resorption pit = cannot demineralize the inorganic component of bone
  • > absent or defective osteoclast acitivty
  • Abnormally thickened bone
  • Fractures
    • No osteon formation
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17
Q

What disease causes these x-rays?

A

Rickets

Due to vitamin D deficiency, cannot calcify cartilage in the zone of provisional calcification (zone 4)

This results in accumulation of cartilage and widening of the growth plate

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18
Q

What is osteoporosis?

A

Bone that is histologically normal but decreased in quantity

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19
Q

What kind of bone is in picture A?

What kind of bone is in picture B?

A
  • A = Cortical (compact) bone
    • Mature
    • Collagen is deposited in circumferential lamellae (osteons/haversian systems form)
  • B = Cancellous (spongy) bone
    • Formed by enchondral ossification
    • Collagen deposited in longitudinal lamellae
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20
Q

Which bone disease is shown in this picture?

A

Paget’s disease

  • Abnormal shadowing on x-ray
  • Cement lines = improper organizaton
    • Bone is mineralized properly, but not laid down in a nice, organized way
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21
Q

What are the two types of mature, lamellar bone?

A

Cortical (compact) bone (A)

Cancellous (spongy) bone (B)

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22
Q

Describe the pathogenesis of Paget’s disease of bone

A

Upregulation of NFKB-osteclastogenesis

  • Mutated p62 sensitizes osteoclast precursors to RANKL
    • p62 is supposed to regulate RANKL-mediated osteoclastogenesis
  • Paramyxovirus stimulates osteoclastogenesis

-> Enhanced resorption capacity

23
Q

Postmenopausal osteoporosis…

  1. Has the exact same pathogenesis as senile osteoporosis
  2. Has a greater effect on cortical bone
  3. Estrogen deficiency results in increased osteoblastic activity
  4. Enhanced osteoclastic activity is the major cause
  5. Considered a low turnover subtype of osteoporosis
A

d. Enhanced osteoclastic activity is the major cause

24
Q

What stage of bone formation is affected by Vitamin D deficiency?

What disease does this result in?

A
  • Children
    • Zone of provisional calcification (zone 4) of growth plates
    • Vitamin D is required for the calcificaiton of the cartilagenous matrix that surroudns chondrocytes
    • Deficiency -> Rickets
  • Adults
    • Vitamin D is required to clacify osteoid to form new adult bone
    • Deficiency -> Osteomalacia
25
Q

Which disorders of bone metabolism result in the inability to calcify organic matrix?

A

Rickets (children) or osteomalacia (adults)

Both result from vitamin D deficiency

26
Q

How does hyperparathyroidism affect bone homeostasis?

A

Hyperparathyroidsim = excessive bone resorption

  • PTH stimulates bone resorption
    • -> osteoclastogenesis -> osteoporosis
27
Q

Describe the pathogenesis of senile osteoporosis

A
  • With aging, osteoblasts become senescent – less effective at forming new bone and growth factors in the matrix lose potency
    • Results in fractures in the hip and vertebra
  • Osteoclasts don’t lose efficacy with age
  • Imbalance results in more bone destruction than formation, leading to osteoporosis
28
Q

What kind of osteoporosis is classified as a “low-turnover” osteoporosis?

A

Senile osteoporosis

Decreased osteoblast activity, normal osteoclast activity

29
Q

Which zone of bone formation is affected by osteopetrosis?

A

Formation of primary bone trabeculae (Zone 5)

30
Q

What causes Rickets?

A

Vitamin D deficiency in children

(Adult version = osteomalacia)

31
Q

What signal stimulates the maturation of osteoclast progenitors into osteoclasts?

A

RANK:RANK Ligand binding

  • Osteoblasts and bone stromal cells secrete RANK ligand
  • RANK is located on the osteoclast progenitor cells
32
Q

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

A

E. Paget’s disease

“collagen matrix madness”

Increased osteoclastogenesis

33
Q

Describe the pathogenesis of postmenopausal osteoporosis

A
  • Loss of estrogen upregulates osteoclastogenic factors and decreases OPG
    • Osteoclastogenic factors = IL-1, IL-6, TNF-alpha
    • OPG = osteoprotegerin (osteoclastogenesis inhibitory factor)
  • -> Osteoclastogenesis
  • Bones with large surface area are most affected
    • Vertebral body
    • Wrist
  • This is a high-turnover osteoporosis
    • ​As soon as they lose acitivity, bone density will decrease
34
Q

What is zone 4?

Which diseases affect this zone?

A

Zone of provisional calcification

  • Rickets aka Osteomalacia
35
Q

Microscopically, lamellar bone differs from woven bone by…​

  1. Having a greater number of osteocytes and osteoblasts
  2. The longitudinal, concentric, and circumferential pattern of collagen deposition in lamellar bone
  3. Presence of calcium in lamellar bone
  4. Its rapid formation in contrast to the slow deposition of woven bone
  5. Absence of Haversian canals in lamellar bone
A

B. The longitudinal, concentric, and circumferential pattern of collagen deposition in lamellar bone

36
Q

What is Paget’s disease of bone?

A

A “collage of matrix madness” due to dyssynchrony of osteoclastic and osteoblastic activity

  • Marked bone resorption followed by rapid new bone formation
  • Bone is mineralized properly, but not laid down correctly
  • This results in bone that looks strong, but is actually very weak due to lack of organization
37
Q

Describe the differences between localized and generalized osteoporosis

A
  • Localized
    • Result of inflammatory focus around the bone, often as a result of autoimmune disorder
  • Generalized
    • Systemic disease. Senile and post-menopausal are most common, can also result from low vitamin D and space travel
38
Q

Describe the presentation of hyperparathyroidism

A

“Moans, bones, renal stones, psychiatric overtones”

  • GI upset
  • Fractures
  • Kidney stones
  • Psych symptoms
39
Q

Ricketts is caused by a defect that affects which zone in the growth plate?

  1. Resting zone
  2. Zone of proliferation
  3. Zone of hypertrophy
  4. Zone of provisional calcification
A

d. Zone of provisional calcification

(zone 4)

40
Q

What kind of bone is A pointing to?

What kind of bone is B pointing to?

A
  • A = osteoid
    • Unmineralized
    • Poorly organized matrix (Type I collagen)
  • B = woven bone
    • Mineralized but not mature
    • Formed rapidly
    • Main component of prepubertal bone
41
Q

What causes osteomalacia?

A

Vitamin D deficiency

Cannot calcify osteoid to form new adult bone

(Children’s version in growth plates = Rickets)

42
Q

What kind of osteoporosis is classified as a “high-turnover” osteoporosis

A

Post-menopausal osteoporosis

Normal-increased osteoblast acitivty, increased osteoclast activity

43
Q

What disease is characterized by a “collage of matrix madness?” – marked bone resorption followed by rapid new bone formation?

A

Paget’s diseae of bone

New bone is mineralized, but not properly laid down; lack of organization = weakness

44
Q

Which bone cells initiate mineralization?

A

Osteoblasts

45
Q

How do osteoclasts resorb bone?

Describe the mechanism

A
  • The osteoclast forms a sealed, acidified microenvironment in resorption pits on the surface of bone
  • H+ ATPase is responsible for acidifying the resorption pit
    • Mutations in the H+ ATPase -> osteopetrosis
  • Minerals and growth factors are released from bone
    • HCL mobilizes the inorganic matrix
    • Cathespsin K degrades the organic matrix (type I collagen)
46
Q

What disease results in these “cutting cones” in the bones?

A

Hyperparathyroidism

Increased osteoclast activity due to PTH secretion

-> Sub-periosteal resorption of bone

47
Q

The organic component of bone is made primarily of
__________,

while the inorganic component is made from
____________.

A

The organic component of bone is made primarily of
collagen type I,

while the inorganic component is made from
calcium hydroxyapatite.

48
Q

Describe (in general) how bone is resorbed in cancellous bone

A
  • Activation of osteoclasts
  • Resorption of bone in Howship’s lacuna
  • Reversal of cell type; osteoclasts become osteoblasts
  • Bone formation
49
Q

A defect in synthesis of Type I collagen results in which bone disease?

Describe the phenotype

A

Osteogenesis imperfecta - brittle bone disease

  • Frequent fractures that heal via excess callus formation
  • Blue sclera
  • Joint laxity
  • Early arthritis

Dominant negative mutation is more severe than decreased synthesis

50
Q

What is osteomalacia?

A

Inability to calcify osteoid in new adult bone during the remodeling process

  • Results from vitamin D deficiency
  • Usually due to chronic renal failure
    • -> Decreased serum Ca2+
    • -> Increased PTH
    • -> Phosphate retention
  • Causes insufficiency fractures on x-ray and bone pain
51
Q

What is the most common cause of osteopetrosis?

A

Mutations in the H+ ATPase pump

  • Results in inability of the osteoclast to acidify the resorption pit
  • Cannot mobilize the inorganic bone matrix
  • -> cannot properly resorb bone -> impaired remodeling​
52
Q

What causes “brown tumor” of bone?

A

Severe hyperparathyroidsim

  • Excessive resorption of bone
  • -> Fracture
  • -> Intramedullary hemorrhage, cyst formation
  • -> “brown tumor”
53
Q

What disease results in an inability to degrade GAGs?

A

Mucopolysaccharidoses (Hunter, Hurler, etc)

Due to lack of lysosomal enzymes

54
Q

What bone disease is this characteristic of?

A

Osteopetrosis

(Absent osteoclast activity due to H+ ATPase defect)

  • Bone lacks medullary canal
  • Star: Hematopoietic bone marrow is replaced by calcified cartilage and new bone

MSK-Derm by Minnie (48 decks)

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