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Musculo-Skeletal > Cellular Structure Of Bone > Flashcards

Cellular Structure Of Bone Flashcards

1
Q

What are the 5 functions of bone?

A

→ Support and movement
→ Protection for internal organs

→ Bone marrow store
→ Mineral reservoir
→ Endocrine

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2
Q

Where is cortical compact bone found?

A

→ On the outside

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3
Q

How is cortical bone organised?

A

→ In sheet like structures

→ Surrounding a hollow structure called the Haversian canal

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4
Q

What are the repeating units of cortical bone?

A

→ Osteons

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5
Q

What are lacunae?

A

→ cell sized holes within the bone matrix

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6
Q

What is the function of Haversian canals?

A

→ Allow for blood vessel penetration

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7
Q

Where is trabecular bone found?

A

→ Near the head of the bone

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8
Q

What is the structure of trabecular bone?

A

→ spongy

→ interlocking struts with spaces inbetween

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9
Q

What is the function of trabecular bone?

A

→ Makes bone lighter

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10
Q

What is the composition of bone in %s?

A

→ Protein : organic osteoid matrix 25%
→ Mineral : 75%

→ Cells

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11
Q

What is the function of the organic protein matrix?

A

→ Gives flexibility and tensile strength

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12
Q

What is bone mineral?

A

→ Hydroxyapatite

→ Calcium and Phosphate

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13
Q

What is the function of bone mineral?

A

→ Gives bone rigidity and compressive strength

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14
Q

What are the 4 types of bone cells?

A

→ Osteoblasts
→ Osteoclasts

→ Osteocytes
→ Bone marrow cells

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15
Q

What are the two subtypes of bone marrow cells?

A

→ Mesenchymal cells

→ Haematopoietic cells

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16
Q

What do mesenchymal stem cells make?

A

→ Osteoblasts and osteocytes

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17
Q

Where are osteoblasts found?

A

→ Lining the inner surface of bone

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18
Q

Where are osteocytes found?

A

→ Encased within the bone matrix
→embedded in lacunae in mature bone
→Connected via processes through canalicular channels

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19
Q

What do haematopoietic stem cells give rise to?

A

→ Lymphoid lineage - lymphocytes
→ Myeloid lineage - RBC and macrophages
→ osteocytes

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20
Q

What are the functions of osteoblasts?

A

→ Bone forming cells
→ Secrete osteoid collagen matrix of bone
→Osteoid is mineralised over time to become mature bone
→Some osteoblasts are embedded in the new bone and differentiate into osteocytes

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21
Q

What are the functions of osteoclasts?

A

→ Bone reabsorbing - digest old bone

→ seal off a portion of bone beneath them from the rest of the microenviroment using the actin ring

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22
Q

What is the life cycle of osteoclasts controlled by?

A

→ Apoptosis

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23
Q

What is a protease that osteoclasts secrete?

A

→ Cathepsin K

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24
Q

What do osteoclasts secrete?

A

→ Acid and proteases that are active in acidic environments

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25
Q

What do osteoclasts look like?

A

→ They are large and multinucleate

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26
Q

What are osteocytes?

A

→ Terminally differentiated osteoblasts

→formed from the fusion of macrophages

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27
Q

What do osteocytes do?

A

→ They lay down bone matrix (organic material that becomes mineralised)

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28
Q

How do osteocytes extend?

A

→ Via multiple dendrites via minute canals in the bone matrix

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29
Q

What is the function of the lacunocanalicular system?

A

→ Maintains communication between the bone surface and blood vessels

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30
Q

How is bone continually renewed?

A

→ Old bone is continually resorbed and new bone is laid down
→ Cycle between osteoclasts digesting old bone and osteoblasts laying down new bone
→whole skeleton has been replaced after 7 years

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31
Q

How does bone remodelling occur?

A

→ The leading edge is where cells differentiate into osteoclasts
→ Behind that the new osteoblasts differentiate into new bone

→ As the osteoblasts lay down the new bone some of them will stay in it where they are encased in lacunae

32
Q

What are the phases of bone remodelling?

A

→microfracture
→resorption
→formation
→repaired bone

33
Q

What are the 3 factors that control bone remodelling?

A

→ Load bearing exercise
→ Paracrine- RANKL, Wnt signalling
→ Endocrine-Estrogen, Thyroid hormone, PTH

34
Q

What is the role of estrogen in bone remodelling?

A

→inhibits osteocyte apoptosis
→ Promotes osteoclast apoptosis

→ essential for skeletal health

35
Q

What process does estrogen favor?

A

→ Formation over resorption

36
Q

What is osteoporosis?

A

→ Loss of bone mass above a certain threshold

37
Q

In what gender is osteoporosis more common in?

A

→ Women

38
Q

Why is osteoporosis more common in women?

A

→ dramatic loss of estrogen due to menopause

39
Q

What is delayed skeletal growth in men linked to?

A

→ Aromatase deficiency

40
Q

What is RANK?

A

→ A surface receptor on pre-osteoclasts that stimulates osteoclast differentiation

41
Q

What is the RANK ligand produced by and what does it do?

A

→ Produced by pre-osteoblasts, osteoblasts and osteocytes

→ binds to RANK and stimulates osteoclast differentiation

42
Q

In what two forms can the RANK ligand exist in?

A

→ Surface bounds

→ Soluble form that is secreted from osteocytes

43
Q

What does the RANK receptor binding promote?

A

→ osteoclast differentiation

44
Q

What is OPG?

A

→ A soluble protein produced by osteocytes

→decoy receptor for RANKL

45
Q

What does OPG do?

A

→ Acts as an antagonist

→ binds to RANK ligand and prevents it from binding to the receptor

46
Q

What ratio controls osteoclast differentiation?

A

→ Ratio of RANK ligand to OPG

47
Q

What are the steps for activating Wnt?

A

→ The frizzled receptor

→ and the co-receptor called LRP5/6 have to interace

48
Q

What is the effector of the Wnt pathway?

A

→ beta catenin

49
Q

What happens after the Wnt pathway is activated?

A

→ beta catenin is translocated to the nucleus where it causes transcription

50
Q

What is the Wnt pathway regulated by?

A

→ inhibited by DKK and Sclerostin

51
Q

Where is sclerostin expressed and what does it do?

A

→ Expressed in osteocytes

→ stops osteoblast differentiation

52
Q

What do OPG and NO do?

A

Inhibit the differentiation of osteoclasts

53
Q

What does the RANK ligand promote?

A

→ Promotes the differentiation of osteoclasts

54
Q

What do PGE2, NO and ATP promote?

A

→ Differentiation of osteoblasts

55
Q

What do sclerostin, DDK and SFRP1 inhibit?

A

→ Inhibit the differentiation of osteoblasts

56
Q

What is a common bone disease?

A

→ Osteoporosis

57
Q

What is a rare bone disease?

A

→ Osteomalacia

58
Q

What is sclerosteosis caused by?

A

→ Mutation of the SOST gene

→ Inactivating sclerostin protein

59
Q

What is osteopetrosis caused by?

A

→ Inactivating the RANK ligand

→ overgrowth of bone

60
Q

What 2 changes occur during osteoporosis?

A

→ Thinning of the cortical bone

→ Widening of the trabecular bone

61
Q

What are the three classifications of bone types?

A

Anatomical bones
Macroscopic structure
Microscopic structure

62
Q

Describe microscopic structure of bones

A

→Woven bone (immature) – initial bone development

→Lamellar bone (mature)

63
Q

Describe cortical bones

A 
→long bones
→80% of skeleton
→Appendicular- appendages 
→80-90% calcified
→mainly structural, mechanical, and protective
64
Q

Describe trabecular bones

A 
→vertebrae & pelvis
→20% of skeleton
axial
→15-25% calcified
→mainly metabolic
→large surface area
65
Q

When does clavicle growth plates fuse?

A

20 years old

66
Q

What are the two types of ossification?

A

Intramembranous ossification

Endochondral ossification

67
Q

Summarise intramembranous ossification

A

→Direct differentiation of osteoblasts from connective tissue
→Flat bones
→Osteoblasts differentiate from mesenchyme precursors

68
Q

Summarise endochondral ossification

A

→Bones form from a cartilage model
→Long bones
→Allows rapid linear growth

69
Q

Describe endochondral ossification

A

→Mesenchymal cells differentiate into chondrocytes that produce a cartilage model
→ becomes hypoxic and dies
→Capillaries penetrate cartilage and deposit bone inside cartilage model, forming primary ossification center.
→Cartilage and chondrocytes continue to grow at ends of the bone while medullary cavity expands and remodels.
→Secondary ossification centers develop after birth.

70
Q

How is the primary ossification centre separated from the secondary?

A

→by growth plate

71
Q

How many zones are there for linear growth?

A 
→reserve zone
→proliferative zone
→hypertrophic zone
→calcification zone
→ossification zone
72
Q

What happens in the reserve zone?

A

→contains small chondrocytes within the matrix.
→do not participate in bone growth
→close to the secondary ossification centre
→proliferate slowly

73
Q

What happens in the proliferative zone?

A

→form column like structure- cells end up further away from epiphysis while undergoing hypertrophic differentiation
→expand in size and express collagen 10

74
Q

What happens in the hypertrophic zone?

A

→Chondrocytes are older and larger than those in the proliferative zone.
→more mature cells are situated closer to the diaphyseal end of the plate.
→ they apoptose leaving behind cartilage mineral matrix which calcifies

75
Q

What does Wnt signalling differentiate?

A

stimulates differentiation of osteoblasts from their mesenchymal precursor

76
Q

What is van Buchem’s?

A

→Enlarged mandible

→Progressive- trapped nerves, headache

Musculo-Skeletal (6 decks)

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