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ESA1 - Body Logistics > Bone > Flashcards

Bone Flashcards

1
Q

What are the two types of bone?

A

Compact (dense)

Spongy (cancellous/trabecular)

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2
Q

What is ossification?

A

Ossification in bone remodelling is the process of laying down new bone material by cells called osteoblasts.

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3
Q

How do most flat bones develop?

A

Intramembranous ossification - directly from mesenchymal tissue

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4
Q

How do long bones develop?

A

Require a cartilage template in order to develop by endochondral ossification

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5
Q

Where does intramembranous ossification take place?

A

Within condensations of mesenchymal tissue and not by replacement of a previous hyaline cartilage template

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6
Q

What are mesenchymal cells?

A

Mesenchymal cells are able to develop into the tissues of the lymphatic and circulatory systems, as well as connective tissues throughout the body, such as bone and cartilage.

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7
Q

What does intramembranous ossification also contribute to?

A

The thickening (not lengthening) of long bones, at their periosteal surfaces (appositional growth)

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8
Q

What are the stages of intramembranous ossification?

A
  • A small cluster of mesenchymal stem cells form a tight cluster of cells (a nidus)
  • The mesenchymal stem cells become osteoprogenitor cells and each develop more Golgi and RER
  • These osteoprogenitor cells become osteoblasts and lay down an extracellular matrix containing Type I collagen (an osteoid)
  • The osteoid mineralises to from rudimentary bone spicules which are surrounded by osteoblasts and contain osteocytes
  • The spicules join to form trabeculae which merge to form woven bone, which is finally replaced by the lamellae of mature compact bone
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9
Q

What is compact bone?

A

Compact bone forms the external surface of the bone and comprises around 80% of the body’s skeletal mass

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10
Q

What is cancellous bone?

A

Cancellous bone forms a network of fine bony columns or plates to combine strength with lightness. The spaces are filled with bone marrow

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11
Q

Which type of ossification is involved when bones develop directly from mesenchymal tissue?`

A

Intramembranous ossification

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12
Q

What do the Haversian and Volkmann’s canals carry?

A

Blood vessels, lymph vessels and nerves

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13
Q

What are some examples of flat bones that develop via intramembranous ossification?

A

Skull, clavicle, scapula and pelvic bones

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14
Q

What is a nidus?

A

A small cluster of mesenchymal stem cells

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15
Q

What are osteoprogenitor cells?

A

These are like the stem cells of bone, source of new osteoblasts

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16
Q

What do osteoprogenitor cells become?

A

Osteoblasts

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17
Q

In the third step of intramembranous ossification, what do the osteoblasts lay down?

A

Extracellular matrix containing type I collagen (osteoid)

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18
Q

What is osteoid?

A

Osteoid is the unmineralized, organic portion of the bone matrix that forms prior to the maturation of bone tissue.

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19
Q

What does the osteoid mineralise to form?

A

Rudimentary bone tissue spicules, which are surrounded by osteoblasts and contain osteocytes

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20
Q

What do the spicules join to form?

A

Trabeculae

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21
Q

What do trabeculae merge to form?

A

Woven bone

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22
Q

What finally replaces woven bone that is formed by the merging of trabeculae?

A

The lamellae of mature compact bone

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23
Q

What is an osteocyte?

A

This is a mature osteoblast that has become embedded in the material it secreted

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24
Q

What is the difference between an osteoblast and an osteoclast?

A

Osteoblasts are responsible for the formation of bone while osteclasts are responsible for resorbing (breaking down) bone

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25
Q

Do osteoclasts have a single nucleus or are they multinucleated?

A

Multinucleated

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26
Q

What is the periosteum?

A

A layer of vascular dense irregular connective tissue that covers the outer surface of all bones (except at the joints of long bones)

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27
Q

What is the endosteum?

A

A thin vascular layer of connective tissue that lines all internal cavities within the bone

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28
Q

What are the functions of the periosteum and endosteum?

A

Nutrition of osseous tissue and provision of a continuous supply of new osteoblasts for repair or growth of bone

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29
Q

What cells do the periosteum and endosteum contain?

A

Osteogenic cells

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30
Q

What are bone spicules?

A

Isolated, newly formed pieces of bone

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31
Q

How do the arrangement of osteocytes differ between immature and mature bone?

A

Immature bone has osteocytes which are randomly arranged while mature bone has osteocytes arranged in the concentric lamellae of osteons.

32
Q

What are canaliculi?

A

Bone canaliculi are microscopic canals between the lacunae of ossified bone.

33
Q

How are nutrients passed between osteocytes?

A

Osteocytes have cytoplasmic processes which reach out to adjacent osteocytes via canaliculi. These processes connect via gap junctions and nutrients can be exchanged.

34
Q

What are the canaliculi also believed to be connected with?

A

The central Haversian canal

35
Q

What does spongy bone consist of?

A

Trabeculae, with the presence of osteocytes lying between lamellae. There are no Haversian or Volkmann’s canals.

36
Q

In spongy bone, what does each trabeculum consist of?

A

Numerous osteocytes embedded within irregular lamellae of bone.

37
Q

Which types of cells lie in the cavities of interconnecting trabeculae of cancellous bone?

A

Adipose and haemopoietic cells

38
Q

What do osteons consist of?

A

Each osteon consists of lamellae of compact bone tissue that surround the Haversian canal

39
Q

Why does bone resist fracture?

A

It has a great tensile and compressive strength as well as a degree of flexibility

40
Q

Why are bones thought to have a degree of flexibility?

A

It is thought that the lamellae are able to slip relative to each other before excessive load causes fracture

41
Q

Why is a haematoma formed between the broken bone ends?

A

When a bone breaks, there is bleeding from multiple broken blood vessels

42
Q

What is granulation tissue?

A

Granulation tissue is new connective tissue and microscopic blood vessels that form on the surfaces of a wound during the healing process

43
Q

What is the first stage of fracture repair?

A

A haematoma is formed in which granulation tissue arises

44
Q

In the second stage of fracture repair, the procallus of granulation tissue is replaced by what?

A

A fibrocartilaginous callus in which bony trabeculae are developing

45
Q

What is the third stage of fractue repair?

A

Endochondral and intramembranous ossification give rise to a bony callus of spongy bone

46
Q

In the final stage of fracture repair, what is cancellous bone replaced by?

A

Compact cortical bone until remodelling is complete

47
Q

Why do bone cells at the edge of the fracture die?

A

No blood supply as blood vessels in bone and periosteum break

48
Q

Which cells remove dead and damaged tissue in a bone fracture?

A

Phagocytc cells and osteoclasts

49
Q

What eventually removes the blood clot formed in a bone fracture?

A

Macrophages

50
Q

What are the stages of bone fracture repair?

A
  1. Haematoma fomation
  2. Fibrocartilaginous callus formation
  3. Bony callus formation
  4. Bone remodelling
51
Q

In bone fracture repair, what do fibroblasts do?

A

Produce collagen fibres that span the break and differentiate into chondroblasts that give rise to a sleeve of hyaline cartilage

52
Q

How long does it take after a fracture for new bone trabeculae to appear in the fibrocartilaginous callus?

A

Within a week

53
Q

What is the fibrocartilaginous callus converted to?

A

Hard (bony) callus of spongy bone

54
Q

What do endochondal and intramembranous ossification do in a bone fracture repair?

A

Ultimately, endochondral ossificationr eplaces all cartilage with spongy bone but intramembranous ossification also produces new spongy bone in the area

55
Q

In young people, how soon do the processes of endochondral/intramembranous ossification in fracture repair begin?

A

Within 2 days

56
Q

How long does bony callus formation continue for?

A

About two months iuntil a very firm union is formed

57
Q

Where is cancellous bone especially remodelling into compact bone during bone fracture repair?

A

Especially in the cortical region - the region of the formed bone shaft walls

58
Q

How long does the process of bone remodelling (final stage of fracture repair) go on for?

A

Several months

59
Q

What removes the material bulging from the outside of the bone and inwads into the medullary cavity?

A

Osteoclasts

60
Q

Why is the final shape of the remodelled area the same as that of the original unbroken bone?

A

This is because it responds to the same set of mechanical stressors

61
Q

If a fracture involves the loss of bone fragments, what is not possible?

A

Bony union and callus formation

62
Q

What does osteoporosis reflect?

A

Enhanced bone resorption relative to formation

63
Q

What is osteoporosis?

A

A metabolic bone disease in which mineralized bone is decreased in mass to the point that it no longer provides adequate mechanical support

64
Q

What characterises the disease of osteoporosis?

A

Depletion of bone mass

65
Q

In osteoporosis what happens to the trabecular bone?

A

Loss of mass/thinning - increased susceptibility to fracture

66
Q

What does osteoporosis associated with aging result from?

A

Incomplete filling of osteoclast resorption bays

67
Q

When does bone mass peak?

A

Between 25-35 years

68
Q

When does bone mass begin to decline?

A

In the 5th or 6th decade

69
Q

Amongst whites, what is the difference in risk of hip fracture between men and women?

A

Women have 2 times the risk of hip fracture than men

70
Q

Amongst whites, what is the difference in risk of vertebral fractures?

A

Women have 8 times he risk of vertebral fractures as men

71
Q

What is Type I osteoporosis?

A

Occurs in postmenopausal women and is due to an increase in the number of osteoclasts as a result of oestrogen withdrawal

72
Q

What is Type 2 osteoporosis?

A

Occurs in elderly people of both genders, often after age 70 and is due to attenuated osteoblast function

73
Q

What are some risk factors associated with osteoporosis?

A

Genetics (peak bone mass higher in black people)

Insufficient calcium intake

Vitamin D deficiency

Exercise

Smoking

74
Q

What is the difference between osteoporosis and osteomalacia?

A

Osteoporosis involves loss of bone mass

Osteomalacia involves softening of bones

75
Q

Why should a fractured bone be immobilised?

A

Protection and alignment

ESA1 - Body Logistics (14 decks)

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