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MSS19 Bone Structure, Remodeling And Repair Flashcards

1
Q

Skeletal system components

A
  1. Bones
  2. Joints + cartilages

2 divisions:

  1. Axial skeleton:
    - skull bones
    - auditory ossicles
    - hyoid bone
    - ribs
    - breastbone
    - back bones
  2. Appendicular skeleton:
    - upper, lower limb bones
    - pectoral girdle (clavicle + scapula)
    - pelvic girdle
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2
Q

Types of bones (according to shape)

A
  1. Long bones (humerus)
  2. Short bones (trapezoid, wrist bone)
  3. Flat bones (sternum)
  4. Irregular bones (vertebra)
  5. Sesamoid bones (patella)
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3
Q

Bone

A
  • one of the hardest tissue
  • Withstand stress (second to cartilage)
  • ***Support + Protection
  • Muscle attachment: systems of lever –> locomotion / limb movement
  • ***Reservoir of Ca / PO4
  • Harbours ***Bone marrow
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4
Q

***Bone vs Cartilage

A

Bone:

  1. Matrix
    - Inorganic (Calcified: hydroxyapatite crystal)
    - Organic (    Collagen type 1 with proteoglycan and glycoprotein)
  2. Hard
  3. Highly vascularized
  4. ***Growth: Appositional only
  5. Cells: osteoblast, osteoclast, osteocyte
  6. Covering: Periosteum
  7. Nutrition: ***Haversian system / osteon (canaliculi)

Cartilage:

  1. Matrix:
    - Non-calcified
    - **    Collagen type 2 (    *hyaline cartilage)
  2. Resilient
  3. Avascular
  4. ***Growth: Appositional + Interstitial
  5. Cells: chondroblasts, chondrocytes
  6. Covering: Perichondrium
  7. Nutrition: ***Diffusion through matrix
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5
Q

Appositional growth (外面) vs Interstitial growth (入面)

A

Bone: only appositional growth (calcified matrix is inexpandible)
- from periosteum + endosteum

Interstitial growth: only possible in cartilage (expandible)

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6
Q

***Bone cells

A
  1. Osteoblasts
    - Bone forming
    - line all bone surfaces
    - derived from **Osteoprogenitor cells (骨幹細胞) (from mesenchymal stem cells) in Periosteum / Endosteum
    - produce **    Organic matrix (Osteoid: Collagen type 1)
    - produce **Ca, PO4-based mineral for Osteoid Calcification
    - characteristics of cells actively synthesizing protein
    - Active stage:
    - -> cuboidal to columnar shape
    - -> **    Basophilic cytoplasm
    - -> ***high alkaline phosphatase activity (regulator of mineralisation)
    - Inactive stage:
    - -> flattened
    - -> low alkaline phosphatase activity
    - once surrounded by newly synthesized matrix –> Osteocytes
  2. Osteocytes
    - **Maintenance of bone matrix (osteocytic osteolysis: transient bone breakdown)
    - **    trapped inside bone matrix (Lacunae) it produced
    - below bone surface (never on bone surface)
    - maintain contact with adjacent osteocytes by thin cytoplasm located in **Canaliculi (microscopic canals between the lacunae of ossified bone: nutrition and communication)
    - average half life of 25 years
    - **    incapable of division
    - death of osteocytes –> resorption of bone matrix
  3. Osteoclasts
    - Bone resorption
    - Removal of bone matrix
    - **Secrete acid, collagenase, other proteolytic enzymes to resorb bone
    - **    Large, **multinucleated mobile cells
    - from **    Granulocyte / Monocyte progenitor cells (吞噬細胞)
    - from **Fusion of circulating monocytes
    - **    Acidophilic cytoplasm
    - Ruffled border to ↑ SA of resorption
    - in Depressions of bone surfaces (    Howship’s lacunae (清除左既痕跡) - resorbed by osteoclasts)
    - ***Clear zone: region of cytoplasm that surrounds the ruffled border to isolate the region of osteolytic activity
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7
Q

Osteoblasts and Osteoclasts

A
  • control dynamic balance of bone tissue

- critical in maintenance, remodeling and repairing of bone

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8
Q

Periosteum and Endosteum

A
  1. Line ***ALL surfaces of bone (exposed bony surface will be resorbed by osteoclasts)
  2. Continuous supply of ***osteoblasts (appositional growth)
  3. Provide nutrition to bone cells (blood vessels in Periosteum)
  4. Important for growth, remodeling and repairing of bone
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9
Q

Periosteum

A
  • cover external surfaces of bone
  • Outer (fibrous) layer: ***Collagen fibres + Fibroblasts
  • Inner (cellular) layer: ***Osteoprogenitor cells (differentiate into Osteoblasts: appositional growth)
  • Sharpey’s fibres - anchor the periosteum to the bone
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10
Q

Endosteum

A
  • cover internal surface of bone
  • line ***marrow cavity
  • ***Osteoprogenitor cells (differentiate into osteoblasts: appositional growth)
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11
Q

Types of bone (according to arrangement of collagen fibres)

A
  1. Primary bone (immature/woven bone)

2. Secondary bone (mature/lamellar bone)

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12
Q

Primary bone vs Secondary bone

A

Primary bone:

  • Primary bony tissue in:
    1. Embryo
    2. During bone repairing
  • ***Random disposition of collagen
  • Temporary: will be replaced by secondary bone

Secondary bone:
- Organised ***Lamellar disposition of collagen (一圈一圈)

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13
Q

Types of bone (according to gross structure in cross section)

A
  1. Compact bone (cortical bone) ***without cavities
  2. Cancellous bone (spongy bone) with ***intercommunicating marrow cavities

Most bones are composed of spongy bone at the core covered by compact bone

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14
Q

Compact bone (Cortical bone)

A

Anatomical / Functional unit: ***Osteon (Haversian system)

  • Concentric lamellae of bone surrounding ***Haversian canal (contain blood vessels, nerves, loose CT)
    —> Bring nutrition to osteocytes in compact bone (through canaliculi)
  • ***Transverse Volkmann’s canals: allow osteon to communicate with other osteons and with the marrow cavity (no concentric lamellae)
  • Complex pattern due to continuous process of bone remodeling
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15
Q

Cancellous bone (Spongy bone)

A

Anatomical / Functional unit:

  • **Trabecula
  • Anastomosing bony ***spicules
  • form meshwork of ***intercommunicating spaces
  • ***Highly vascular
  • contain ***red bone marrow
  • weaker, ***more flexible and greater SA
  • suitable for metabolic activity
  • ***Interconvertible with compact bone
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16
Q

Osteogenesis

A

according to origins of development

  1. Intramembranous ossification: most flat bones
  2. Endochondral ossification: most long bones

–> no major difference in histological structure!

17
Q

***Intramembranous ossification (由mesenchyme tissue入面lay bone)

A
  • source of Flat bones
  • takes place within condensation of mesenchymal tissue (membranous structure)
  • ***No intermediate stage of cartilage
  • ***Direct differentiation of mesenchymal cells into osteogenic cells to deposit bones
  • Steps:
    1. Mesenchymal cells ***directly differentiate into osteoblasts
  1. New bone matrix synthesized and mineralized by osteoblasts
  2. Osteoblasts trapped —> Osteocytes
  3. Surrounding CT becomes Periosteum of new bone
  4. Replacement of primary bone to form secondary bone (involves bone resorption and bone formation)
  5. **Thickening of flat bone by **appositional growth
18
Q

***Endochondral ossification (由cartilage入面lay bone)

A
  • takes place within cartilage
  • responsible for formation of Long and Short bones
  • ***Cartilage then replaced by bone
  • important for ***elongation of long bone
  • Steps:
    1. ***Proliferation + Hypertrophy of chondrocytes
  1. **Death of chondrocytes —> **Calcification of cartilage
  2. ***Resorption of cartilage by Osteoclasts from surrounding periosteum (derived from perichondrium)
  3. Invasion of ***Osteogenic bud (osteoprogenitor cells and blood vessels) from periosteum
  4. Osteoprogenitor cells differentiate into Osteoblasts
  5. Synthesis of new bone matrix onto surface of calcified cartilage (basophilic in appearance) (向外伸展lay new bone)
  6. Remodeling to replace new bones by mature bones
  7. Osteoclasts resorb bone within diaphysis —> creating hollow medullary cavity
19
Q

***5 zones of epiphyseal (growth) plate from epiphyseal side of epiphyseal cartilage

A

***RPHCO

  1. Resting zone (最出)
    - resting hyaline cartilage
  2. Proliferative zone
    - chondrocytes divide rapidly and form columns of stacked cells ***along long axis of the bone (∴向longitudinal發展)
  3. Hypertrophic cartilage zone
    - chondrocytes undergo hypertrophy
  4. Calcified cartilage zone
    - death of chondrocytes and calcification of cartilage
  5. Ossification (resorption) zone (最入)
    - bone formation by osteoblasts (from osteogenic bud) —> lay bone onto calcified cartilage
20
Q

Parts of bone

A
  1. Epiphysis (2 ends of long bone, covered with articular cartilage)
  2. Metaphysis (narrow portion between epiphysis and diaphysis, contains the growth plate during childhood)
  3. Diaphysis (main / midsection, made up of compact bone)
21
Q

Bone remodeling

A
  • constant lifelong process
  • involve both bone resorption and formation
  • adjusting bone architecture
  • repairing fractures and micro-damage
  • important in maintaining plasma ***Ca homeostasis
22
Q

***Balance between bone formation and resorption

A
  1. Growth hormone / IGF-1
    - ↑ chondrocyte + osteoblasts proliferation
  2. Calcitonin
    - ↓ osteoclast activity (bone resorption), ↓ plasma Ca level
  3. Testosterone / estrogen
    - ↑ bone formation
    - ↓ bone resorption
  4. Parathyroid hormone
    - ↑ bone resorption —> ↑ plasma Ca level
    - ↑ Ca absorption in kidney (and small intestine)
23
Q

***Bone repairing

A
  1. Inflammatory stage
    - Inflammatory cells and Fibroblasts infiltrate bone
    - Granulation tissue formation
    - Vascular tissue ingrowth
    - Mesenchymal cells migration
  2. Reparative stage
    - ***Callus formation (fibrous and cartilaginous)
    - Woven bone formation and endochondral ossification
  3. Remodeling stage
    - remodeling to original bone shape

***Overall:
Inflammatory cells + Fibroblast —> Granulation tissue —> Vascular ingrowth —> Mesenchymal migration —> Callus —> Woven bone —> Endochondral ossification —> Remodeling

24
Q

Cartilage

A
  • Avascular
  • obtain nutrient by diffusion through ECM
  • ECM:
  • -> collagen type 2, except fibrocartilage with type 1
  • -> enriched with GAGs + proteoglycans
  • resilient (more compressible than bone)
  • main functions:
    1. support soft tissue
    2. **shock-absorbing
    3. **    joint movement
  • 3 types:
    1. Hyaline cartilage (essential for growth of long bone)
    2. Elastic cartilage
    3. Fibrocartilage
  • Cartilage cells:
    1. Chondroblasts (earliest chondrogenic cells to synthesize and secrete ECM)
    2. Chondrocytes (located in matrix cavities / lacunae)
  • Perichondrium:
  • -> dense CT surrounding most cartilages (except articular cartilage at joint surface)
  • -> vascular supply for cartilage
  • -> Chondrogenic: cells in innermost layer differentiate into chondroblasts
25
Q

Hyaline cartilage (most common)

A
  • bluish-white, translucent
  • temporary skeleton in foetus, gradually replaced by bone
  • present at:
    1. **Epiphyseal plate: responsible for longitudinal growth of bone
    2. **    Articular cartilage at joints
    3. Walls of ***respiratory passages
  • Matrix:
    1. Collagen type 2
    2. Proteoglycan aggregates: proteoglycan-GAGs (**chondroitin sulfate and **keratan sulfate) linked to core proteins associated with ***hyaluronic acid (another type of GAG)
    3. Chondronectin (glycoprotein)
    4. High water content
  • Cells:
    1. Isogenic group
    2. Proliferating chondrocytes accumulated in rows in epiphyseal plate
    3. Fill lacunae completely, shrink during histological preparation
    4. Have organelles typical of protein secretory cells (elaborate rER, well-devloped Golgi) –> synthesize the matrix
26
Q

Elastic cartilage

A
  • found in **auricle of ear, walls of external auditory canal, auditory tube, **epiglottis, ***cuneiform cartilage of larynx
  • abundant network of ***elastic fibres in addition to collagen type 2
  • also possess perichondrium
27
Q

Fibrocartilage

A
  • characteristics intermediate between dense CT and hyaline cartilage
  • found in
    1. **IV disks
    2. **    Ligament attachment to cartilaginous surface of bone
    3. ***Pubic symphysis
  • chondrocytes arranged in long rows (in lacunae)
  • Type 1 collagen aligned in parallel arrangement along chondrocytes
  • less amorphous matrix
  • ***no identifiable perichondrium
28
Q

Chondrogenesis

A

Initial stage: (interstitial growth)

  1. From mesenchyme
  2. Mesenchymal cells differentiate into chondroblasts –> synthesize cartilage matrix (begins from ***centre of mesenchyme)
  3. Chondroblasts separate from each other (Interstitial growth)
  4. Surrounding mesenchymal cells will become future perichondrium which remains chondrogenic

Later stage: (appositional growth)

  1. Cells at inner layer of perichondrium differentiate into chondroblasts (for Appositional growth)
  2. Regeneration of cartilage by perichondrium
29
Q

2 types of cartilage growth

A
  1. Interstitial growth
    - from pre-existing chondroblasts
    - occurs at early phase of cartilage formation
    - at epiphyseal plate
    - impossible in bone
  2. Appositional growth
    - from chondroblasts at inner layer of perichondrium (similar to bone)
30
Q

Appositional vs Interstitial growth

A

Appositional:

  • ***growth from outside
  • chondroblasts in perichondrium secrete matrix (***onto surface of pre-existing cartilage)
  • ↑ Width

Interstitial:

  • ***growth from within
  • chondroblasts divide and secrete matrix (from within lacunae)
  • ↑ Length
  • more matrix —> make cartilage ***more dense
31
Q

Summary types of bones

A

According to shape:

  1. Long bones (humerus)
  2. Short bones (trapezoid, wrist bone)
  3. Flat bones (sternum)
  4. Irregular bones (vertebra)
  5. Sesamoid bones (patella)

According to ***Arrangement of collagen fibres:

  1. Primary bone (immature/woven bone)
  2. Secondary bone (mature/lamellar bone)

According to ***Gross structure in cross section:

  1. Cortical bone (compact bone) without cavities
  2. Spongy bone (cancellous/trabecular bone) with intercommunicating marrow cavities

MSS (32 decks)

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