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Histology > Bones > Flashcards

Bones Flashcards

1
Q

What is an Osteon?

A

“cylindrical” arrangements of bone matrix parallel to the long axis of the bone

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2
Q

What are Haversian Canals?

A

“vertical” channels containing neurovascular elements and bone cells

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3
Q

What are Volkmann’s canals?

A

horizontal” channels containing neurovascular elements and bone cells

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4
Q

What are concentric lamellae?

A

concentric rings of bone matrix centered on a Haversian canal

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5
Q

What are interstitial lamellae?

A

Areas of bone matrix between osteons

Possibly remnants of remodeling

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6
Q

What are lacunae?

A

holes between the bone lamellae which house osteocytes

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7
Q

What are Canaliculi?

A

small tubes spanning the bone lamellae which allow osteocytic interaction

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8
Q

What are inner and outer circumferential lamellae?

A

lamellar bone that separates osteons from endosteum and periosteum respectively

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9
Q

What are Osteogenic cells?

A

overtly undifferentiated cell derived from embryonic mesenchyme

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10
Q

Where are Osteogenic cells found?

A

Line endosteum, periosteum, Haversian canals and Volkmann’s canals
Appear as a very flattened cell lining these surfaces

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11
Q

What is the function of osteogenic cells?

A

Mitotic cell that retains the ability to differentiate into an osteoblast
Participate in wound repair and remodeling by providing cells for those processes

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12
Q

What makes up the organic matrix of bone?

A

1) Predominately Type I collagen fibers and associated bone specific GAG’s
2) Osteonectin -extracellular protein that anchors hydroxyapatite to collagen
3) Osteocalcin -extracellular protein that binds calcium

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13
Q

What makes up the inorganic matrix of bone?

A

Hydroxyappetite

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14
Q

What are Osteoblasts?

A

derived as a result of osteogenic cell.mitosis

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15
Q

What are the 4 places that appositional growth can occur?

A

Haversian Canals
Volkmann’s canals
Periosteum
Endosteum

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16
Q

Where are osteoblasts located?

A

Line endosteum, periosteum, Haversian canals and Volkmann’s canals
Appear as a cuboidal or polygonal cell lining these surfaces

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17
Q

What is the function of osteoblasts?

A

secretes the organic, unmineralized matrix of bone (osteoid)

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18
Q

What are osteocytes?

A

terminal stage of bone cell maturation

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19
Q

Where are osteocytes located?

A

located in a lacunae surrounded by matrix it secreted previously as an osteoblast
Remains in contact (ie., gap junctions) with other osteocytes via canaliculi

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20
Q

What is the function of osteocytes?

A

Relatively inactive cell that no longer secretes matrix appreciably
Retains an ability to secrete and resorb (ie., maintain) matrix to a small extent

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21
Q

What are osteoclasts?

A

derived from monocytes (circulating white blood cell)

22
Q

Where are osteoclasts found?

A

Found on “resorptive surfaces” known as Howship’s lacuna

Very large, multinucleated cell (20~100 micrometers, 2-50 nuclei)

23
Q

What is the function of osteoclasts?

A

Secrete lysosomal enzymes extracellularly to resorb surplus or inferior bone matrix
Essential component of bone growth and repair (ie., bone remodeling)

24
Q

How do osteoblasts become osteocytes?

A

The osteoblasts are essentially left behind while the growth occurs and they remain connected to osteoblasts but since they are suspended they are known as osteoclasts

25
Q

How are nutrients and wastes transferred in and out of osteo cells?

A

Nutrients and wastes are transferred through diffusion from the Haversian canals to lacunae

26
Q

What are the characteristics of bone matrix?

A

bone matrix is highly resistant to bending, twisting, compression and stretch·

27
Q

What is the organic portion of bone matrix also known as?

A

Osteoid

28
Q

What does the organic portion of bone matrix consist of?

A

1) Predominately Type I collagen fibers and associated bone specific GAG’s
2) Osteonectin -extracellular protein that anchors hydroxyapatite to collagen
3) Osteocalcin -extracellular protein that binds calcium

29
Q

What if the inorganic portion of bone matrix made of?

A

Predominately hydroxyapatite crystals

• crystalline complexes of calcium and phosphate

30
Q

Which comprises of more total bone weight, the organic portion or inorganic portion of bone matrix?

A

Inorganic portion (65% of total bone weight)

31
Q

What are the requirements for mineralization of osteoid?

A

1) a surface on which apositional growth may occur
2) extracellular calcium and phosphate levels at or above a mininum threshold level
3) osteoblasts

32
Q

What is the process of mineralization of osteoid? (may need to look on page 16, won’t fit on one card)

A

1) osteoblasts synthesize and exocytose the organic components of osteoid
2) osteoblasts exocytose previously stored vesicles containing calcium and phosphate
~this results in a local increase in extracellular calcium and phosphate
~calcium and phosphate begin precipitating here to form hydroxyapatite crystals
4) these local points of crystal formation serve as seeds for larger crystals to form
5) the hydroxyapatite crystals enlarge rapidly by accretion of more calcium/phosphate
6) eventually the forming crystals merge to produce a layer of fully mineralized matrix
7)osteocytes form as osteoblasts get caught up in matrix lacuna
8) canaliculi form as hydroxyapatite crystallizes around preexisting osteocyte cell
processes
9) HaversianNolkmanns canals form as hydroxyapatite crystallizes around BV’s

33
Q

Where are the only places that osteoblasts and osteogenic cells are found?

A

Periosteum
Endosteum
Haversian canal
Volkmann’s canal

34
Q

What is an osteosarcoma?

A

1) malignant tumor of osteoblasts
2) most common in children in the long bones at the knee
3) osteoid does not mineralize completely and the legs bow at the knee
(osteoblasts are not mature enough and end up being extremely weak)

35
Q

What is an osteoid osteoma?

A

Benign tumor of osteoblasts
Manifests itself as bony nodules forming on various bones
Osteoid becomes excessively mineralized in these areas

36
Q

What is Osteomalacia?

A

1) Softening of the bones resulting in increased tendency to fracture
2) osteoblasts are apparently normal
3) failure to mineralize is a result of decreased serum calcium & phophate

37
Q

What are rickets?

A

1) essentially osteomalacia in children leading to permanent deformities
2) typically the osteoid in the long leg bones mineralizes poorly
3) failure to mineralize is often attributed to a Vitamin D deficiency

38
Q

What is bone remodeling?

A

balance between bone deposition (osteoblasts) and bone resorption (osteoclasts)

39
Q

What does bone remodeling occur in response to?

A

1) hormonal balances in the body
2) mechanical stresses put on the bone
3) morphological changes occurring as a result of bone growth or repair

40
Q

What is parathormone?

A

hormone secreted by parathyroid gland

41
Q

What is the function of parathormone?

A

stimulates osteoclast activity leading to increased serum calcium levels

42
Q

What are some synergistic effects of parathormone?

A

1) stimulates small intestinal epithelial cells to absorb calcium
2) stimulates kidney tubule epithelial cells to reabsorb calcium
3) stimulates kidney tubule epithelial cells excrete phosphate

43
Q

What is calcitonin?

A

hormone secreted by thyroid gland

44
Q

What is the function of calcitonin?

A

antagonizes parathormone by decreasing osteoclast activity

45
Q

What is Osteoporosis?

A

1) commonly seen in bed-ridden people and postmenopausal women
2) excessive osteoclast activity results in a loss of bone matrix
3) bone resorption exceeds reparative bone deposition by osteoblasts
4) the weakened matrix results in an increasing tendency to fracture

46
Q

What is Paget’s Disease?

A

1) bones are larger in size but weaker in structure than normal bones
2) presumed to be a disorder of excessive osteoclast activity
3) osteoblasts go overboard trying to repair the lost matrix
4) reparative matrix is woven instead of lamellar (and prone to fracture) (woven bone = temporary bone)

47
Q

Bone is constantly being remodeled, true or false?

A

True (on a day to day basis as well as over a lifetime)

48
Q

What is a cutting cone?

A

Resorption canal created by osteoclasts during remodeling

49
Q

What is a closing cone?

A

new concentric lamellae laid by osteoblasts to fill resorption canal

50
Q

What is the process of fracture repair? (Page 18)

A

1) Phagocytic cells (macrophages) clean up the injury site
2) Fibroblasts and capillaries grow into the injury site
- Granulation tissue -loose CT initially produced by fibroblasts and periosteal cells
- Callus - denser fibrocartilaginous tissue that next forms (stabilizes and binds the fracture)
3) Osteoblasts move into area and initiate endochondral ossification
• new bone forms initially at some distance from fracture and grows toward fracture
• Bony callus-the ossified replacement for the original callus
(this begins as woven bone and is gradually remodeled to lamellar bone)
4) Remodeling restores the integrity of the compact bone
5) Remodeling restores the continuity of the marrow cavity
6) Process typically takes 6-12 weeks depending on the nature and severity of fracture
7) Setting the bone typically speeds the restoration and improves the structural integrity

Histology (9 decks)

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