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Histology > Bone And Ossification > Flashcards

Bone And Ossification Flashcards

1
Q

2 ways in which bone is formed

A

Endochondral ossification
Intramembranous ossificatiom

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2
Q

Endochondral ossification

A

Transformation of a pre-existing cartilaginous model or proformer

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3
Q

Intramembranous ossification

A

Direct ossification of a primitive mesenchymal connective tissue

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4
Q

What is the first stage of long bone formation

A

Creation of cartilaginous models or proformers
Subsequently converted to bone

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5
Q

What are proformers made of

A

Hyaline cartilage

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6
Q

Hyaline cartilage of proformers synthesis

A

By chondroblasts
Produce a glassy amorphous looking matrix within which the cells become trapped causing them to transform into less synthetically active chondrocytes

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7
Q

Formation of chondroblasts

A

Differentiate from progenitor cells within embryonic connective tissue (mesenchyme)

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8
Q

What encapsulates hyaline cartilage

A

Fibrous perichondrium that contains both progenitor cells and differentiated chondroblasts

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9
Q

Major component of osteoid

A

Type 1 collagen

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10
Q

Primary bone

A

First type of bone to be produced in a developing bone

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11
Q

Structure of primary bone

A

Randomly woven collagen
Calcium is amorphous not crystalline

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12
Q

What type of bone is present at birth

A

Primary bone

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13
Q

Structure of secondary bone

A

Collagen organised into regularly arranged laminae
Calcium deposited as hydroxyapatite with the long axes of the crystals parallel to the collagen fibres

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14
Q

Characteristics of secondary bone

A

Light
Strong

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15
Q

How can secondary bone occur

A

Woven bone (open framework)
Compact lamellae
Osteons

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16
Q

Osteoclasts

A

Occur frequently in developing bone
Multinucleated cells
Digest bone and play a part in remodelling

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17
Q

Original of osteoblasts

A

Differentiate from precursor cells contained within capsule of the proformer or that arrive in the cavity of developing bone via the blood stream

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18
Q

Which cells produce bone

A

Osteoblasts

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19
Q

Osteocytes

A

When the osteoid is ossified osteoblasts become trapped within the matrix where they regress into a less active form

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20
Q

How is contact between osteocytes maintained

A

By minute canaliculi within the bone through which spidery processes from the osteocytes make contact with each ither

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21
Q

When are long bones first created

A

2nd trimester

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22
Q

How do long bones start in utero

A

Hyaline cartilage proformers

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23
Q

Which type of cartilage is particularly responsive to growth and sex hormones

A

Epiphyseal cartilage

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24
Q

Growth plates

A

Continue to exist beyond puberty and are largely responsible for the lengthening of bones during childhood and adolescence

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25
Q

1st stage of endochondral ossification

A

Formation of hyaline cartilage proformers

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26
Q

2nd stage of endochondral ossification

A

The shaft (diaphysis) of the proformer becomes calcified and a bony collar is established around it

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27
Q

3rd stage of endochondral ossification

A

The bony collar is penetrated by blood vessels that bring in more osteoprogenitor cells that differentiate into osteoblasts and lay down bone

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28
Q

4th stage of endochondral ossification

A

A primary centre of ossification is established- involves the erosion of the proformer cartilage and formation of primary bone

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29
Q

6th stage of endochondral ossification

A

Later secondary centres of ossification of formed in the heads (epiphyses) of the bones

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30
Q

7th stage of endochondral ossification

A

As the primary and secondary centres expand the amount of cartilage is reduced so that it becomes restructure to the epiphyseal growth plates that separate the diaphysis from the epiphyses and to the articular surfaces of the bones

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31
Q

Epiphyses

A

Heads of the bines

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32
Q

Diaphysis

A

Shaft of the proformer

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33
Q

Where is a primary centre of ossification established

A

Bony collar around diaphyssi

34
Q

Where is secondary centre of ossification established

A

Epiphyses

35
Q

Zone of hyperplasia

A

Chondrocytes of resting cartilage first divide creating columns of progeny

36
Q

Zone of hypertrophy

A

Newly formed cells grow, eroding the cartilage matrix as they enlarge

37
Q

What remains after zone of hypertrophy

A

Thin spicules of cartilage
The chondrocytes themselves having been released from the matrix and resorbed

38
Q

Zone of ossification

A

Remnant strands of cartilage become calcified and serve as a substrate to which osteoblasts become attached
Osteoblasts then lay down primary bone

39
Q

Appositional growth

A

Bone is eroded and re-deposited in the outside of the shaft of the bone

40
Q

How does the length of a long bone grow

A

At a epiphyseal growth plate
Zone of hyperplasia
Zone of hypertrophy
Zone of ossification

41
Q

How does the girth of a long bone increase

A

Appositional growth

42
Q

Where does intramembranous ossification occur

A

Flat bones of the skull

43
Q

When does intramembranous ossification start

A

Second trimester

44
Q

Which type of bone formation requires a proformer

A

Endochondral ossification

45
Q

1st stage of intramembranous ossification

A

Small clusters of progenitor cells within a primitive mesenchyme transform into osteoblasts and start to deposit isolated islands of bone

46
Q

2nd stage of intramembranous ossification

A

As the islands enlarge they coalesce to create an open network of bone

47
Q

3rd stage of intramembranous ossification

A

Osteoblasts continue to deposit bone on the mesh work until the holes become filled in thereby creating a plate of primary bone

48
Q

4th stage of intramembranous ossification

A

Primary bone is eroded and replaced with denser more organised lamellar secondary bone

49
Q

What is the end product of osteogenesis

A

Mature secondary bone

50
Q

Composition of mature bone

A

5% hydroxyapatite

51
Q

How is bone examined

A

Native bone is ground into thin slithers with grinding paste

52
Q

Why is the bone specimen not stained

A

Contrast is created by refraction caused by the crystalline nature of the tissue

53
Q

How is bone treated for examination

A

Treated with acid and/or chelating agents
-procedure removes most of the calcium but organic components are retained

54
Q

What colour does compact lamellar secondary bone stain

A

Purple/pink

55
Q

What part of the compact lamellar bone stains strongly

A

The collagen matric

56
Q

What surrounds bone

A

Periosteum

57
Q

Periosteum

A

Outer fibrous layer
Inner cellular layer - paler staining
Site of osteoprogenitor cells

58
Q

Inner cellular layer of periosteum

A

Contains rows of dark blue staining osteoblasts

59
Q

How does hyaline cartilage normally obtain its oxygen and nutrients

A

Small pieces of cartilage do not have a direct blood supply, the oxygen and nutrients diffuse through the matrix from the blood vessels in the perichondrium
Large masses of cartilage have a conventional blood supply via a capillary bed- during osteogenesis the diaphysis and epiphyses of bone proformers are invaded by blood vessels

60
Q

In which part of a long bone does ossification first occur

A

Diaphysis

61
Q

Approximately what proportion of primary centres of ossification have formed by the time of birth

A

Almost all have started to ossify and some are well advanced by this time
Carpal and tarsal bones have not begun to ossify

62
Q

Which long bones only have a single epiphyseal growth plate

A

Distal phalanges of fingers and toes

63
Q

Which are the last sets of bones to begin the process of ossification

A

Carpal and tarsal bone - begin at age 7/8

64
Q

Why does the cytoplasm of osteoblasts stain purple blue

A

Cells synthesise large quantities of osteoid
Contain a profuse endoplasmic reticulum with large numbers of ribosomes attached to it
Ribosomes and DNA stain dark blue

65
Q

What are Volkmann’s canals

A

Cross connections between the Haversian canals of adjacent osteons

66
Q

Where on a long bone does cartilage persist even after the closure of the growth plate

A

At the ends as articular cartilage

67
Q

Which hormone promotes the breakdown of bone

A

Parathormone

68
Q

Howship’s lacunae

A

Depressions in the surface of bone formed by osteoclasts

69
Q

How to describe bone by origin

A

Primary (woven)
Secondary (lamellar)

70
Q

How to describe bone by mode of formation

A

Membranous
Endochondrial

71
Q

How to describe bone by gross appearance

A

Spongy/cancellous
Compact

72
Q

How to describe bone by formed

A

Osteons
Appositinal

73
Q

Osteoid

A

Extracellular matrix rich in type 1 collagen, glycosaminoglycans and proteoglycans

74
Q

Osteons

A

Central Haversian canal containing blood vessel
Surrounded by concentric rings of lamellar bone with osteocytes

Secondary bine

75
Q

Synovium

A

Lines the inside of joint capsule
1-4 layers of synovial cells
Type A - phagocytes
Type B - rich in rER
Variable shapes- squamous to cuboidal
Richly vascular
Highly innervated

76
Q

Type A synovial cells

A

Phagocytes

77
Q

Type B synovial cells

A

Secrete synovial fluid
Rich in rER

78
Q

Osteoclasts:
Are derived from megakaryocytes
Are multinucleated
Differentiate into osteoprogenitor cells
Lie in Haversian canals
Synthesise osteoid

A

Multinucleated

79
Q

Osteocytes:
Are dead cells
Do not communicate with each other
Have more endoplasmic reticulum than osteoblasts
Lie on the surface of bones
May resorb formed bone matrix

A

May resorb formed bone matrix

80
Q

Which of these bones is formed by intramembranous ossification?

Clavicle
Femur
Humerus
Ischium
Scaphoid

A

Clavicle

81
Q

Why bones are formed by intermembranous ossification

A

Flat bones of skull
Clavicle
Mandible

82
Q

Which of the following can be found in Haversian canals?

Blood vessels
Haematopoietic marrow
Osteoclasts
Osteocytes
Sharpey’s fibres

A

Blood vessels

Histology (17 decks)

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