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MSS Weeks 3-5 > Bone Cell Biology > Flashcards

Bone Cell Biology Flashcards

1
Q

What is the function of bone?

A
  • Infrastructure - Bone marrow - Specialized connective tissue - bone is calcified extracellular matrix - Reservoir of Ca phosphate
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2
Q

How is Calcium released from bone?

A
  • PTH induces osteoclasts to reabsorb bone and release calcium
  • Calcitonin antagonizes these processes
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3
Q

What are the cells in bone?

A

Osteoblasts

Osteocytes

Osteoclasts

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4
Q

The matrix is made up of __% inorganic and __% organic stuff

A

70%; 30%

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5
Q

What is the mineral component of bone?

A

Hydroxyapatite

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6
Q

What makes up hydroxyapatite?

A

Calcium and phosphorous

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7
Q

What is osteoid made up of?

A
  • Type I collagen
  • Proteoglycans
  • Glycoproteins
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8
Q

What makes bone acidophilic?

A

Type I Collagen

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9
Q

What is the function of glycoprotein in bone?

A

Promotes hydroxyapatite formation

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10
Q

What makes bone hard?

A

Combined hydroxyapatite and collagen type I

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11
Q

What are some differences between bone and cartilage?

A
  • Bone: 70% mineral, 25% water, Type I collagen, Neuronal and vascular structures
  • Hyaline Cartilage: no minerals, 75% water, type II collagen; no neuronal or vascular structures
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12
Q

________ are specialized fibroblasts

A

osteoblasts

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13
Q

What are the two osteoblast specific genes?

A
  • Cbfa-1: transcription factor bone = master gene
  • Osteocalcin
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14
Q

What is the name of the proteins (growth factors) that induce osteoblast differentiation

A

Bone morphogenetic proteins (BMPs)

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15
Q

What do osteoblasts do?

A

Make osteoid - Type I collagen and glycoproteins

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16
Q

How is bone formation completed?

A

Osteocalcin-mediated deposition of calcium within the osteoid

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17
Q

Where are Osteocytes found?

A

Occupy lacunae between layers (lamellae) of bone matrix

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18
Q

What is the half life of osteocytes

A

25 years

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19
Q

How many osteocytes are there per lacuna?

A

1

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20
Q

How are gap junctions formed between osteocytes

A

Cytoplasmic processes penetrate the matrix (through canaliculi) where they join processes of other osteocytes

21
Q

What to Osteoclasts do?

A

Destroy/remodel bone

22
Q

How are osteoclasts developed?

A

Developed from macrophages that fuse together (multinuclear)

23
Q

What is “Howship’s lacunae”?

A

Hollow areas of matrix where osteoclasts reside

24
Q

Why do osteoclasts form a ruffled border?

A

Osteoclasts are polarized and the active side forms the appearance of a ruffled border

25
Q

How are osteoclasts regulated?

A

Hormones:

  • Calcitonin = inhibits
  • PTH = activates
    • Lysosomes manufacture cathepsin K which is secreted into the microenvironment
    • Acid is also released into the microenvironment
26
Q

Where are these cell located?

Osteoblasts:

Osteocytes:

Osteoclasts:

A

Osteoblasts: in the periosteum with smaller numbers in the endosteum

Osteocytes: within lacunae of the bony matrix between the periosteum and endosteum

Osteoclasts: Mostly found attached to bony matrix on the endosteal side

27
Q

What is the difference between compact bone and spongy bone?

A

Compact bone - dense, no cavitation

Spongy - cavitation

* both look identical microscopically

28
Q

What makes of flat bone?

What makes up long bone?

A
  • Flat bone (calvaria) -
    • 2 plates of compact bone surround spongy bone
  • Long bone:
    • Diaphesis: compact with spongy bone lining marrow
    • Epiphesis: Caps of compact bone around spongy bone
29
Q

Define Osteon

A

Cylinder with concentric lamellae

30
Q

What are the two perpendicular canals in bone and what do they contain?

A

Haversian canals and Volkmanns canals

They contain blood vessels, nerves, and lymph

31
Q

What are the two ways bone develops?

A
  1. Intramembranous: osteoblasts deposit osteoid onto mesoderm
  2. Endochondral: osteoblasts deposit osteoid onto cartilage
32
Q

In order to build bone, what must happened first?

A

Calcification of cartilage

33
Q

Endochondral development: at the diaphysis -

A

Osteoblasts invade calcified cartilage - Secrete osteoid leading to ossification

34
Q

Endochondral development: at the epiphyses -

A
  • Same process as at the diaphysis
  • Articular cartilage remains at ends of bone
  • Epiphyseal plate cartilage on opposite side of epiphysis - for growth in length
35
Q

How do long bones get long?

A

Sex steroid hormones go to the pituitary causing the release of growth hormone which leads to the liver’s release of somatomedin (IGF-1) which induces proliferation

36
Q

What are the zones of growth in the long bones?

A
  • Zone of proliferation
  • Zone of hypertrophy
  • Zone of calcification (basophilic)
  • Zone of ossification
37
Q

In calcification, what type of collage is present

A

Collagen II must be replaced by Collagen X for calcification

38
Q

Explain Fracture repair

A
  • Macrophages remove debris
  • Chondroblasts secrete a callus of hyaline cartilage
  • Osteoblasts replace cartilaginous calus with bony callus
  • Primary bone is replaced by lamellar secondary bone
39
Q

What type of procedures are available for bone tissue engineering?

A
  • Bone morphogenetic proteins: BMP-2 and BMP-7
  • Adult stem cells (MSCs) that can become osteoblasts
  • Growth factors or cells (or both) are implanted within biodegradable ‘sponges’ made of collagen I
40
Q

We get a new skeleton every ___ years

A

10

41
Q

Diseases of remodeling

A
  • Osteopetrosis: dense heavy bone; osteoclasts lack ruffled border
  • Osteoporosis: resorption by osteoclasts outpaces osteogenesis leading to hollow fragile bones
42
Q

Osteoporosis prevention and screening?

A
  • Prevention: dietary calcium; vitamin D (improves absorption of calcium) weight bearing exercise
  • Screening: bone mineral density; compare BMD with young normal subjects every 2-5 years
43
Q

How are osteoclasts produced?

A

Stromal cells induced by PTH to secrete:

  • M-CSF - induces macrophage proliferation
  • RANK-L - induces macrophage differentiation into osteoclasts
  • OPG - osteoprotegerin antagonizes RANK_L by binding to its receptor
44
Q

What inhibits osteoblasts?

What induces them?

A

Leptin inhibits

BMP induce

45
Q

What inhibits osteoclasts?

What induces?

A
  • Inhibited by calcitonin and osteoprotegerin
  • Induced by RANK
46
Q

What is the PTH paradox?

A

PTH induces both osteoblasts and osteoclasts - this is because osteoblast formation is favored with spikes of concentration of PTH; constant PTH favors osteoclast formation

47
Q

Anabolic drugs that are pro osteoblast

A

PTH 1-34 = teriparatide

48
Q

Anti-resorptive drugs = anti osteoclast

A
  • SERMS (selective estrogen receptor modulators) - Raloxifene
  • Bisphosphonates (Bonivia)
  • Calcitonin

MSS Weeks 3-5 (22 decks)

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