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Organisation of the Body: Tissues > Bone Morphology > Flashcards

Bone Morphology Flashcards

1
Q

What is found in the bone ECM?

A

Collagen, calcium hydroxyapatite crystals, proteoglycans and glycoproteins

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2
Q

What is collagen’s function in bone?

A

Gives tensile strength

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3
Q

How are collagen helices organised?

A

arranged at different angles in different lamellae

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4
Q

Calcium Hydroxyapatite crystals function

A

compressive strength

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5
Q

How are the crystals structured?

A

Attached to collagen fibres by Osteonectin

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6
Q

What are the crystals a source of?

A

Phosphate ions and calcium

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7
Q

What evidence is there to show the function of collagen and the calcium hydroxyapatite crystals?

A

Add acid, will demineralise the bone leaving only collagen. The resultant bone is stretchy. Add heat, will denature the collagen leaving a very brittle bone.

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8
Q

Proteoglycan functions

A

Bind to the collagen hydroxyapatite matrix to shield the crystals from the destructive effects of temperature and chemical agents.

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9
Q

4 main glycoproteins

A

Osteonectin, osteocalcin, osteopontin and Bone Morphogenic Factor

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10
Q

Osteonectin function and which main cells secrete it

A

binds calcium hydroxyapatite crystals and collagen and initiates mineralisation. Secreted by osteoblasts and fibroblasts

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11
Q

Osteocalcin function and which cell secretes it

A

In its carboxylated form, osteocalcin binds calcium ions. Secreted solely by osteoblasts

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12
Q

Osteopontin function

A

Thought to anchor osteoclasts to mineral matrix of bone

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13
Q

Bone Morphogenic Factor function

A

induce the formation of new cartilage and bone

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14
Q

Main bone cells

A

Osteoblasts, osteoclasts and osteocytes

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15
Q

Osteoblast function

A

Growing cells which synthesise and secrete organic components into the bone matrix, such as collagen, glycoproteins and proteoglycans

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16
Q

Where are osteoblasts located?

A

localised exclusively at the bone surface

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17
Q

How are osteoblasts anchored and bound to one another?

A

Attached to the bone matrix by integrins. Bound to each other by adherent and gap junctions

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18
Q

What happens once the Osteoblasts have completed their function?

A

Begin differentiation into osteocytes and migrate into the matrix where they become entrapped by lacunae. Osteocalcin then binds calcium ions locally. Differentiating osteoblasts also secrete membrane enclosed matrix vesicles containing alkaline phosphates whose role are to increase the phosphate ion concentration in the matrix. High concentration of both these ions enable the hydroxyapatite crystals to form.

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19
Q

Osteocyte function and location

A

Inactive cells that serve as mechanosensors, detecting the mechanical load and stress on the bone and thus can trigger bone remedial action. Entrapped in lacunae within osteons

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20
Q

What do osteocytes produce during the transition from an osteoblast?

A

Dendritic processes which become surrounded by calcifying matrix that eventually become canaliculi.

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21
Q

What occurs in the canaliculi?

A

Canaliculi contain a small volume of interstitial fluid whereto diffusion of metabolites between osteocytes and blood vessels takes place

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22
Q

How do osteocytes communicate with one another and other cells?

A

Via gap junctions present at the dendritic processes

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23
Q

Difference in osteocyte organelle composition compared to osteoblasts

A

less RER, smaller Golgi and more condensed nuclear chromatin

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24
Q

Osteoclasts function

A

Essential for matrix resorption during bone growth and remodelling

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25
Q

Osteoclast size and nuclei number

A

very large, multiple nuclei

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26
Q

Briefly how osteoclasts work

A

Attach via integrins to arg-gly-asp (RGD) sequences in the matrix protein osteopontin. Form ruffled edges facing sealed Howship’s Lacuna, where they secrete acid and proteases which breaks down the bone matrix.

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27
Q

Connective tissues of the bone

A

Endosteum and periosteum

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28
Q

Periosteum outer layer

A

Outer fibrous layer of dense connective tissue, containing mainly type 1 collagen, with fibroblasts and blood vessels. Bundles of periosteum collagen, perforating fibres, penetrate the bone matrix and bind to it. Blood vessels branch and penetrate the bone too.

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29
Q

periosteum inner layer

A

more cellular, includes osteoblasts, bone lining cells and mesenchymal cells, called the osteoprogenitor cells.

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30
Q

What are the osteoprogenitor cells?

A

mesenchymal stem cells

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31
Q

What bones does the periosteum cover?

A

Outer surface of all bones but joints of the long bones

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32
Q

Where is the endosteum found?

A

covers small trabecular of bony matrix that projects into the marrow cavities (medullary cavity)

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33
Q

Endosteum structure

A

contains osteoprogenitor cells, osteoblasts and bone lining cells, within a sparse, delicate matrix of collagen fibres

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34
Q

Two types of bone

A

Trabecular (cancellous) and compact (cortical)

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35
Q

Where is cancellous bone found?

A

Epiphyses, short bone cores, around the central marrow cavity of the diaphyses,

36
Q

Where is cortical bone found?

A

Surface of epiphyses, surface of short bones, almost entirety of long bones.

37
Q

Two types of cancellous bone organisation

A

Lamellar bone and woven bone

38
Q

How is lamellar bone characterised?

A

Multiple layers of lamellae of calcified matrix- organised in parallel sheets of concentrically around a central canal

39
Q

What is an osteon?

A

A complex of concentric lamellae with a central canal (Haversian canal) containing small blood vessels, nerves and endosteum.

40
Q

What is found between the successive lamellae?

A

lacunae containing osteocytes

41
Q

What is the outer boundary of the osteon called and what it contains?

A

cement line, with non collagen proteins, minerals and collagen

42
Q

How many concentric lamellae does each osteon have?

A

5-20

43
Q

How do the canals communicate with each other?

A

Through transverse perforating (Volkmann canals) canals

44
Q

What is found between the osteons?

A

Interstitial lamellae

45
Q

What is interstitial lamellae and how is it formed?

A

Groups of parallel lamellae which are remainders of osteons partially destroyed by osteoclasts during growth and remodelling of bone

46
Q

Other lamellae and their location and function

A

external circumferential lamellae, immediately beneath the periosteum. Inner circumferential lamellae, around the marrow cavities. Both enclose and strengthen the middle regions of bone containing osteons.

47
Q

How is woven bone characterised?

A

Non-lamellar with a random disposition of type 1 collagen

48
Q

What bone tissue is the first to appear in embryonic development?

A

Woven bone tissue

49
Q

Where is woven bone found?

A

Embryos, in recent fracture repair, however temporary in adults. Permanently found in the insertions of some tendons and sutures of the calvaria

50
Q

what is osteogenesis?

A

bone development

51
Q

Two osteogenetic processes

A

intramembranous ossification and endochondral ossification

52
Q

What bones are formed by intramembranous ossification?

A

most flat bones, such as the bones of the skull and jaw, as well as the scapula and clavicle

53
Q

Where does bone formation begin?

A

Within condensed mesenchyme ossification centers?

54
Q

What are ossification centers?

A

areas in which osteoprogenitor cells arise, proliferate and form incomplete layers go osteoblasts around a network of developing blood vessels

55
Q

What is the first stage of intramembranous ossification?

A

Osteoblasts secrete organic matrix components at the cell surface in contact with existing bone material, producing a collagen rich layer called osteoid.

56
Q

Osteoid location

A

between osteoblasts and existing bone

57
Q

Next stage of intramembranous ossification

A

Osteoid calcifies, forming small regions of woven bone with osteocytes trapped in lacunae.

58
Q

What causes the fusion of ossification centres?

A

continued matrix secretion and calcification

59
Q

Final stage

A

woven bone matrix replaced by compact bone that encloses a region of cancellous bone

60
Q

What gives rise to the endosteum and periosteum

A

mesenchymal regions that do not undergo ossification

61
Q

Where does endochondral ossification take place?

A

the epiphyses of long bones, within hyaline cartilage . However also takes place in the majority of bones

62
Q

Where does the process of endochondral ossification begin?

A

Occurs in the bone collar, produced by osteoblasts within the perichondrium (transitioning into the periosteum) around the diaphysis cartilage.

63
Q

Bone collar function

A

impedes diffusion of oxygen and nutrients into the cartilage, causing local chondrocytes to hypertrophy and compress the surrounding matrix, initiating calcification by releasing osteocalcin and alkaline phosphatase

64
Q

What happens to the chondrocytes?

A

Hypertrophic chondrocytes die, leaving empty spaces in the calcified matrix

65
Q

What occurs next in endochondral ossification?

A

Blood vessels from the old perichondrium penetrate the bone collar, bringing osteoprogenitor cells and osteoblasts into the central region, which produce woven bone.

66
Q

Where does endochondral ossification occur in the beginning of embryonic development?

A

Primary ossification centres of the diaphysis

67
Q

Where does endochondral ossification occur later?

A

Secondary ossification centres of the epiphysis

68
Q

Which two regions of cartilage remain after endochondral ossification?

A

Articular cartilage and epiphyseal plate

69
Q

Where is articular cartilage?

A

Between joints of long bones

70
Q

Where is the epiphyseal plate + function?

A

Connects the epiphysis to the diaphysis and allows the longitudinal bone growth in children

71
Q

5 Distinct regions of cellular activity at the epiphyseal growth plate

A

Zone of reserve, proliferative zone. zone of hypertrophy, zone of calcified cartilage, zone of ossification

72
Q

Explain each of the 5 zones

A

Zone of reserve- composed of hyaline cartilage

Proliferative zone- cartilage cells divide, enlarge and secrete more type II collagen and proteoglycans. Become organised into columns parallel to the long axis of bone

Zone of hypertrophy- swollen, terminally differentiate chondrocytes, compress matrix into aligned spicules. Secretes type X collagen, preventing diffusion into the matrix

Zone of calcified cartilage- chondrocytes about to undergo apoptosis release matrix containing alkaline phosphatase and osteocalcin to begin matrix calcification

Zone of ossification- formation of woven bone

73
Q

Where does longitudinal growth take place?

A

Cell proliferation of growth plate

74
Q

Process of growth of the circumference

A

appositional growth

75
Q

Process of appositional growth

A
  1. Osteoblasts release Osteoclast Differentiation factor (RANKL) and macrophage colony stimulating factor.
  2. the RANKL is the osteoclast receptor activator, initiating resorption
  3. Integrins in osteoclast membrane seal onto the bone at the Howship’s Lacunae forming a sealing zone.
  4. A ruffled border develops at the contact zone
  5. Osteoclasts start to produce and secrete hydrogen ions via a proton pump
  6. Carbonic anhydrase produces more hydrogen ions by producing carbonic acid
  7. Chloride is exchanged for the bicarbonate produced by a membrane exchanger
  8. Chloride channel enables chloride to pass into the lacuna and produce HCL
  9. Proteases secreted to break down collagen and other proteins in the bone tissue
  10. Calcium and signalling peptides from the degrading bone stimulate osteoblasts to secrete matrix and replace the bone
76
Q

What is the function of the sealing zone?

A

Able to produce a specialised microenvironment between the osteoclast and matrix

77
Q

How is calcium released from bones?

A

Parathyroid Hormone (PTH) from the parathyroid glands stimulates osteoclasts to resorb bone matrix, releasing calcium ions.

78
Q

What form of action does PTH use?

A

Indirect- targets osteoblasts which respond by releasing RANKL, which in turn activate osteoclasts

79
Q

How are elevated calcium levels lowered?

A

Calcitonin, produced by thyroid gland acts directly on osteoclasts, slowing matrix resorption and bone turnover.

80
Q

Where is bone marrow found?

A

Within spongy and cancellous portions of bone

81
Q

Bone marrow components

A

hematopoietic cells, marrow adipose tissue and supportive stromal cells.

82
Q

Bone marrow function

A

Store fat and formation of new blood cells

83
Q

accretion definition

A

growth by adding multiple layers

84
Q

example of accretion

A

appositional growth

85
Q

blood supply of bones

A

nutrient artery and vein enter at the nutrient foramen at the centre of the diaphysis

forms metaphyseal artery and vein and then epiphyseal artery and vein

Organisation of the Body: Tissues (10 decks)

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