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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
What do osteoclasts look like?
→ They are large and multinucleate
26
What are osteocytes?
→ Terminally differentiated osteoblasts | →formed from the fusion of macrophages
27
What do osteocytes do?
→ They lay down bone matrix (organic material that becomes mineralised)
28
How do osteocytes extend?
→ Via multiple dendrites via minute canals in the bone matrix
29
What is the function of the lacunocanalicular system?
→ Maintains communication between the bone surface and blood vessels
30
How is bone continually renewed?
→ 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
31
How does bone remodelling occur?
→ 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
What are the phases of bone remodelling?
→microfracture →resorption →formation →repaired bone
33
What are the 3 factors that control bone remodelling?
→ Load bearing exercise → Paracrine- RANKL, Wnt signalling → Endocrine-Estrogen, Thyroid hormone, PTH
34
What is the role of estrogen in bone remodelling?
→inhibits osteocyte apoptosis → Promotes osteoclast apoptosis → essential for skeletal health
35
What process does estrogen favor?
→ Formation over resorption
36
What is osteoporosis?
→ Loss of bone mass above a certain threshold
37
In what gender is osteoporosis more common in?
→ Women
38
Why is osteoporosis more common in women?
→ dramatic loss of estrogen due to menopause
39
What is delayed skeletal growth in men linked to?
→ Aromatase deficiency
40
What is RANK?
→ A surface receptor on pre-osteoclasts that stimulates osteoclast differentiation
41
What is the RANK ligand produced by and what does it do?
→ Produced by pre-osteoblasts, osteoblasts and osteocytes | → binds to RANK and stimulates osteoclast differentiation
42
In what two forms can the RANK ligand exist in?
→ Surface bounds | → Soluble form that is secreted from osteocytes
43
What does the RANK receptor binding promote?
→ osteoclast differentiation
44
What is OPG?
→ A soluble protein produced by osteocytes | →decoy receptor for RANKL
45
What does OPG do?
→ Acts as an antagonist | → binds to RANK ligand and prevents it from binding to the receptor
46
What ratio controls osteoclast differentiation?
→ Ratio of RANK ligand to OPG
47
What are the steps for activating Wnt?
→ The frizzled receptor | → and the co-receptor called LRP5/6 have to interace
48
What is the effector of the Wnt pathway?
→ beta catenin
49
What happens after the Wnt pathway is activated?
→ beta catenin is translocated to the nucleus where it causes transcription
50
What is the Wnt pathway regulated by?
→ inhibited by DKK and Sclerostin
51
Where is sclerostin expressed and what does it do?
→ Expressed in osteocytes | → stops osteoblast differentiation
52
What do OPG and NO do?
Inhibit the differentiation of osteoclasts
53
What does the RANK ligand promote?
→ Promotes the differentiation of osteoclasts
54
What do PGE2, NO and ATP promote?
→ Differentiation of osteoblasts
55
What do sclerostin, DDK and SFRP1 inhibit?
→ Inhibit the differentiation of osteoblasts
56
What is a common bone disease?
→ Osteoporosis
57
What is a rare bone disease?
→ Osteomalacia
58
What is sclerosteosis caused by?
→ Mutation of the SOST gene | → Inactivating sclerostin protein
59
What is osteopetrosis caused by?
→ Inactivating the RANK ligand | → overgrowth of bone
60
What 2 changes occur during osteoporosis?
→ Thinning of the cortical bone | → Widening of the trabecular bone
61
What are the three classifications of bone types?
Anatomical bones Macroscopic structure Microscopic structure
62
Describe microscopic structure of bones
→Woven bone (immature) – initial bone development | →Lamellar bone (mature)
63
Describe cortical bones
``` →long bones →80% of skeleton →Appendicular- appendages →80-90% calcified →mainly structural, mechanical, and protective ```
64
Describe trabecular bones
``` →vertebrae & pelvis →20% of skeleton axial →15-25% calcified →mainly metabolic →large surface area ```
65
When does clavicle growth plates fuse?
20 years old
66
What are the two types of ossification?
Intramembranous ossification | Endochondral ossification
67
Summarise intramembranous ossification
→Direct differentiation of osteoblasts from connective tissue →Flat bones →Osteoblasts differentiate from mesenchyme precursors
68
Summarise endochondral ossification
→Bones form from a cartilage model →Long bones →Allows rapid linear growth
69
Describe endochondral ossification
→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
How is the primary ossification centre separated from the secondary?
→by growth plate
71
How many zones are there for linear growth?
``` →reserve zone →proliferative zone →hypertrophic zone →calcification zone →ossification zone ```
72
What happens in the reserve zone?
→contains small chondrocytes within the matrix. →do not participate in bone growth →close to the secondary ossification centre →proliferate slowly
73
What happens in the proliferative zone?
→form column like structure- cells end up further away from epiphysis while undergoing hypertrophic differentiation →expand in size and express collagen 10
74
What happens in the hypertrophic zone?
→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
What does Wnt signalling differentiate?
stimulates differentiation of osteoblasts from their mesenchymal precursor
76
What is van Buchem's?
→Enlarged mandible | →Progressive- trapped nerves, headache

Musculo-Skeletal (6 decks)

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