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SYSTEMIC PATHOLOGY - 1 > 11 – Bone Intro > Flashcards

11 – Bone Intro Flashcards

1
Q

Bone

A
  • Connective tissue with its cells embedded in a mineralized ECM
  • *tissue, organ and part of skeleton
  • ECM: 90-95% of volume
  • Cells: 5-10% of volume
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2
Q

Connective tissues are composed of

A
  • Mesenchymal cells of mesodermal origin
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3
Q

Extracellular matrix of bone components

A
  • Organic:
  • Inorganic:
  • Water: 10% of weight
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4
Q

Organic component of ECM of bone

A
  • Collagen in form of osteoid
  • 20-25% of weight
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5
Q

Osteoid

A
  • Major organic component of ECM before it is mineralized
  • 90% fibers (type 1 collagen)
  • 10% amorphous ground substance that binds to hydroxyapatite
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6
Q

Amorphous ground substance of osteoid

A
  • Conjugated proteins (AA attached to a non-protein chemical)
  • Proteoglycans
  • lipids
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7
Q

Inorganic component of ECM of bone

A
  • Ca and P in form of hydroxyapatite (HAP)
  • 65-70% of weight
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8
Q

Apatite is any group of minerals with the general formula of

A
  • 10Ca : 6 PO4 (-3) : X-
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9
Q

Two families of bone cells

A
  1. Form and maintain bone: derived from mesenchymal stem cells in bone marrow
  2. Reabsorb: derived from hematopoietic stem cells of monocyte series found in bone marrow
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10
Q

What are the three types of bone cells?

A
  • Osteoblasts
    o Active and inactive
  • Osteoclasts
  • Osteocytes
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11
Q

Active osteoblasts

A
  • Plump bone forming cells
  • Line all bone-forming surfaces
  • Produce bone matrix (osteoid)
  • Initiate mineralization of matrix
  • Initiate bone resorption
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12
Q

Inactive osteoblasts

A
  • Flat cells
  • ‘bone-lining’ cells
  • Line surfaces where NO bone formation or resorption is occurring
  • Rapidly release Ca from bone if the blood Ca concentration is low
  • Protect bone from chemical insults
  • Can become active osteoblasts to form new bone
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13
Q

Osteocytes

A
  • Embedded in mineralized ECM
  • Located in lacunae
  • Communicate with other osteocytes and bone lining cells of endosteum and periosteum via cell processes
  • Detect forces place on bone and signal osteoblasts
  • Role in maintaining ECM and plasma Ca
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14
Q

Canaliculi

A
  • Little canals withing mineralized ECM that contain osteocyte processes
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15
Q

Osteoclasts

A
  • Multinucleated giant cells formed from fusion of hematopoietic stem cells of monocytes series in bone marrow, circulate in blood or both
  • *only cells capable of bone reabsorption
  • Create concavities in bone surfaces
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16
Q

For osteoclasts to resorb bone, they must attach to…

A
  • Bone surface, normally lined by osteoblasts
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17
Q

Howship’s or resorption lacunae

A
  • Concavities in bone surfaces created by the osteoclasts
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18
Q

Compact bone

A
  • Relatively large proportion of bone
  • Small proportion of interosseous space
  • *composed of lamellar bone
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19
Q

Lamellar bone

A
  • Mature bone (organized)
  • Collagen fibers of ECM arranged in parallel layers (concentric rings)
  • *most of adult skeleton is lamellar bone
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20
Q

Cortical bone

A
  • Compact bone comprising of outer layer of bone (cortex)
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21
Q

Cancellous (lattice-like) bone

A
  • Anastomosing plates or trabeculae of bone
  • Relatively large proportion of interosseous space
  • Aka trabecular, spongy, lattice, or reticular bone
  • *composed of either woven or lamellar bone
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22
Q

Woven bone (immature, reactive or new bone)

A
  • Collage fibers of ECM appear haphazardly woven together
  • Temporary bone
  • Provides short-term support (development or repair)
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23
Q

Woven bone is present

A
  • Fetal ossification centers
  • Leading edge of growing bones
  • Around teeth
  • Points of attachment of tendons and ligaments
  • Response to injury, inflammation or neoplasia
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24
Q

Spongiosa

A
  • Spicules (sharp, needle-like bodies)
  • Composed partially or entirely of bone near the leading edges of ossification centers
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25
Q

Primary spongiosa

A
  • Temporary spongiosa formed initially during ossification
  • Composed mostly of calcified cartilage covered with woven bone
    o May contain some lamellar bone
26
Q

Secondary spongiosa

A
  • Thicker than primary spongiosa
  • Result of remodelling (replacement of calcified cartilage and woven bone with lamellar bone)
27
Q

Modeling (shaping)

A
  • CHANGE in size, shape or contour
  • Normal growth, altered mechanical use or disease
  • Undergo mostly resorption or mostly formation depending on stimulus
28
Q

Wolff’s law

A
  • Bone (normal or abnormal) develops the structure most suited to resist the FORCES acting upon it
29
Q

Remodelling (renewal)

A
  • Normal and continuous REPLACEMENT of existing or old bone with new bone
  • *resorption and formation are LINKED and occur at equal rates
30
Q

What are the 4 major functions of bone?

A
  1. Structural support
  2. Protection of vital organs
  3. Mechanical advantage
  4. Reservoir
    *acid-base homeostasis AND trap for hazardous materials (ex. lead)
31
Q

Bone as a reservoir: % of Ca and phosphorus

A
  • Ca: 99%
  • Phosphorus: 85%
32
Q

5 classifications of bone by shape

A
  1. Flat
  2. Irregular
  3. Tubular (long)
  4. Sesamoid
  5. Short (cuboidal)
33
Q

Flat and irregular bones are characteristic of the

A
  • Axial skeleton
34
Q

What are 2 types of fetal ossification?

A
  1. Intramembranous ossification
  2. Endochondral ossification
35
Q

Intramembranous ossification

A
  • *Results in membrane or membranous bones
  • Begins with condensation of mesenchymal cells
    o Some differentiate into OSTEOBLASTS and begin to form osteoid that is quickly mineralized to form spicules of woven bone
    o Increase in size and coalesce to form a continuous piece of bone
  • Ex. some bones of skull (maxillae and portions of mandibles)
36
Q

Endochondral ossification

A
  • *result in cartilaginous bone
  • Begins with condensation of mesenchymal cells
    o Differentiated into CHONDROBLASTS that form a cartilaginous model
    o Mature to chondrocytes
  • AVASCULAR and devoid of stem cells
    o w/o blood supply=degenerates and calcifies
  • **REPLACEMENT OF CARTILAGE WITH BONE
37
Q

Further development of endochondral ossification model depends on

A
  • depends on neovascularization
  • repopulation of model with stem cells
  • production of woven bone via endochondral ossification
38
Q

What are some examples of cartilaginous bone?

A
  • Tubular bones
  • Vertebrae
  • Pelvic bones
39
Q

Articular cartilage

A
  • Thin layer of hyaline cartilage on articular surfaces of bone that form synovial joints
40
Q

Epiphyseal cartilage

A
  • Cartilage between articular cartilage and outer surface of epiphysis
41
Q

Subchondral bone

A
  • Bone below or deep to the cartilage
  • Ex. could be articular cartilage
42
Q

Cortical bone

A
  • Compact bone of cortex of the diaphysis
43
Q

Diaphysis

A
  • Elongated cylindrical portion of tubular bone that separate the 2 ends
  • Composed of cortex surrounding the medullary cavity
  • *site of primary center of ossification
44
Q

Endosteum

A
  • Like the periosteum
  • Lines the internal surfaces of bones including
    o Medullary cavity
    o Trabecular bone
    o Osteonal canals
45
Q

Epiphysis

A
  • Wide end of tubular bone
  • Covered by articular cartilage
  • In growing bones is separated from metaphysis by the physis
  • *site of secondary ossification
  • Bone might have 2 epiphyses
  • Contains blood vessels which provide nutrition to physis
46
Q

Medullary cavity

A
  • Space in diaphysis filled with marrow
47
Q

Metaphysis

A
  • Wider parts of tubular bone between diaphysis and physis
  • Composed of thin cortex surrounding cancellous bone
  • Growing bones: cancellous bone is made of primary and secondary spongiosa
48
Q

Periosteum

A
  • Specialized fibrous connective tissue
  • Contains bone cells
  • Covers external surfaces of bones (except articular surfaces)
49
Q

Perichondral ring

A
  • Dense layer of fibrous connective tissue that is CONTINUOUS with periosteum but overlies the periphery of a physis
50
Q

Physis

A
  • Growth plate
  • Disk of hyaline cartilage of growing chondral bones located between the metaphysis and epiphysis
  • *temporary structure
51
Q

When is the physis the thickest?

A
  • When growth is most rapid
  • *becomes thin as growth slows
52
Q

Trabecular bone

A
  • Less dense bone found in metaphysis and epiphyses of tubular bone
  • Also called cancellous bone and spongy bone
53
Q

Appositional growth

A
  • *GROWTH IN DIAMETER
  • Deposition of successive layers upon those already present
  • *while periosteum adds new bone, endosteum removes bone via osteoclastic activity to increase the diameter of the medullary cavity
  • *keep cortex in relative proportion
54
Q

Growth in length of endochondral bones

A
  • Endochondral ossification allows endochondral bones to withstand functional stresses while maintaining ability to grow in length
55
Q

What is responsible for most of the growth in length with endochondral ossification?

A
  • Endochondral ossification at physes
  • Within the EPIphyses contributes to a lesser degree
56
Q

When does growth stop?

A
  • When the physis in ENTIRELY replaced by bone
  • *closure of growth plate=marks skeletal maturity
57
Q

4 zones of the physis

A
  1. Reserve or resting zone
  2. Proliferative zone
  3. Hypertrophic zone
  4. Calcifying zone
58
Q

Reserve zone (physis)

A
  • Hyaline cartilage
  • Serves as a source of cells for the proliferative zone
59
Q

Proliferative zone (physis)

A
  • Clusters of cartilage cells multiply via successive mitotic divisions
  • Forms columns of chondrocytes
  • *contributes to growth (minimally) by adding new cells to the physis
60
Q

Hypertrophic zone (physis)

A
  • Chondrocytes
  • Lacunae become greatly enlarged and account for most of growth in length
  • Chondrocyte cytoplasm becomes vacuolated and nuclear and cell membranes fragment (consistent with apoptosis)
61
Q

Calcifying zone (physis)

A
  • Intercellular material (chondrocyte ECM) becomes mineralized or calcified
    o Mineralization is necessary for phagocytic cells (ex. chondroclasts to attach and remove cartilage during remodelling)
62
Q

What is in the osteogenic zone?

A
  • Capillary loops from metaphysis invade between the columns of calcified cartilage
  • Transverse septa are removed by chondroclasts=allows lacunae to merge and form larger spaces surrounded by calcified cartilage
  • *contiguous surfaces become lined by osteoblasts which produce woven bone

SYSTEMIC PATHOLOGY - 1 (11 decks)

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