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SGUL - Physiology 2 > MSS: Cellular Structure Of The Bone > Flashcards

MSS: Cellular Structure Of The Bone Flashcards

1
Q

What does the skeleton consist of?

A
  • Axial and Appendicular skeleton
  • Axial: Skull, neck, vertebral column, Thoracic cage
  • Appendicular: Upper and Lower limbs, Pectoral and Pelvic girdle
  • Articulated by cartilaginous joints
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2
Q

What is the importance of bones?

A
  • Physical support, maintain posture, space, and delineation of spaces
  • Protection of vital structures, e.g. brain, heart, lungs
  • Mechanical basis of movement. Attachment for muscles and tendons, allows for leverage
  • Storage of salts, including calcium, resource sink
  • Haematopoiesis, location of red bone marrow, new blood cells
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3
Q

What is a bone made out of?

A
  • Connective tissues, covered by hyaline cartilage or periosteum
  • Organic framework layered with inorganic minerals
  • Combination of organic/inorganic gives strength and flexibility
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4
Q

What is the organic components of the bone?

A

Organic (35%): collagen fibres (ossein) and some ground substance forming the bone matrix.

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5
Q

What is the inorganic components of the bone?

A

Inorganic (65%): Mostly calcium hydroxyapatite (Ca10(PO4)6(OH)2) crystals which calcify the ossein
- Main storage of calcium, phosphorus
- Minerals are removed and added as the body needs

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6
Q

Describe the organic components of the bone in more detail

A
  • Type 1 collagen (85-90%), some collagen V, trace III, XI, XIII
  • Ground substance from non collagenous proteins
  • Key to development, remodelling, Growth, Repair
    4 major groups
  • Proteoglycan macromolecules
  • Multiadhesive glycoproteins
  • Bone-specific, vitamin K–dependent proteins
  • Growth factors and cytokines
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7
Q

What are the 3 classifications of the bone?

A

Anatomical, Microscopic structure and Macroscopic structure

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8
Q

List some of the anatomical classifications of the bone

A
  • Flat
  • Long
  • Short
  • Irregular
  • Sesamoid
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9
Q

List some of the macroscopic structures of the bone

A
  • Cancellous (spongy, medullary)
  • Cortical (compact)
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10
Q

List some of the microscopic structures of the bone

A
  • Woven (primary, immature)
  • Lamellar (secondary, mature)
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11
Q

Describe the microscopic structure of the bone in more detail (PART 1)

A

Woven bone (immature, primary bone)
- Random assortment of collagen fibres interlacing
- Temporary bone, in fetuses or where the bone is being repaired after a break
- Can also be found where remodelling happens, attachments of tendons and alveolar sockets of teeth

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12
Q

Describe the microscopic structure of the bone in more detail (PART 2)

A

Lamellar bone (mature, secondary)
- Organised concentric layers (lamellae)
- Organised into osteons
- Circular in compact bone
- Fewer cells and ground substance, more mineralised

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13
Q

Describe the Macroscopic structure of the bone in more detail

A

Cortical (compact) bone forms exterior
- 80% of bone (by mass)
- Very dense
- Most of the strength of the bone

Cancellous (spongy) bone deep to the cortical, forming the interior
- Network of bony trabeculae, lighter, supports cortical bone while minimising weight
- Spaces filled with marrow

  • Medullary cavity in long bones, lined with cortical, full of marrow
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14
Q

Describe the structure of the cancellous bone

A
  • Lighter, weaker and more flexible
  • Set up in trabeculae, when mature these run in the direction of stress
  • Higher surface area to volume ratio, more suitable for metabolic activity
  • Space between the trabeculae filled in with bone marrow, red or yellow
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15
Q

What are some anatomical bone classifications?

A

Check lecture video

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16
Q

What are the Periosteum anatomical properties of the bone?

A

Lines external surface of bones
•Exception: where articulating, then hyaline cartilage

Inner cellular layer
- Contains osteoprogenitors (stem cells) if actively growin/remodelling bone
- In grown bone, contains periosteal cells

Outer fibrous layer
- Collagen fibres arranged parallel to bone surface
- Exception: where ligaments and tendons attach, extend oblique/right angles and continuous with collagen in these

17
Q

What are the bone cavities anatomical properties of the bone?

A
  • Lined with endosteum, usually 1 cell layer of bone lining cells and osteoprogenitors
  • Marrow cavity, and spaces between spongy bone trabeculae
  • Contain red and yellow marrow
  • Red marrow: centre of haematopoiesis
  • Yellow marrow: in adults less new blood cells needed, adipose tissue. Can revert
  • In adults, red marrow in limited locations
18
Q

Describe the osteoprogenitor bone cells

A
  • From mesenchymal stem cells in bone marrow
  • On external and internal surfaces, and vascular canals
  • Runt-related transcription factor 2 (RUNX2) triggers differentiation
19
Q

What is the use of IGF 1 and IGF 2 in Osteoprogenitor cells?

A
  • IGF 1 and IGF 2 stimulate osteoprogenitor proliferation + differentiation to osteoblasts
  • Also bone morphogenic factors
  • Also Pulsed electromagnetic stimulation (witchcraft)
20
Q

Describe the role of Osteoblasts in bone cells

A
  • Secretes type 1 collagen and bone matrix proteins (form osteoid)
  • Involved in the calcification process

Secretes small matrix vessels
- Single layer in contact with forming bone

Some become embedded in the forming bone
- Specialise into osteocytes

21
Q

Describe the role and structure of Osteocytes in bone cells (PART 1)

A
  • Mature bone cell enclosed by bone matrix it secreted as an osteoblast
  • Smaller, more processes
  • Following mineralisation, it occupies a lacuna (space) conformed to its shape
22
Q

Describe the role and structure of Osteocytes in bone cells (PART 2)

A
  • Cytoplasmic processes extend through canaliculi
  • Communiocate with other osteocytes/bone cells via gap junctions
  • Metabolically active, maintain bone, actively detect and respond to mechanical forces
  • Flexing of bone moves interstial fluid through canniculi
23
Q

What are bone lining cells?

A
  • Also osteoblast derived
  • Flat cells, few organelles
  • In sites where no bone remodelling is taking place, cover the bone surface
  • Periosteal cells on external surface
  • Endosteal cells on internal surface
  • Maintain and nutritionally support embedded osteocytes
  • Regulate calcium/phosphate flow
24
Q

What are osteons?

A
  • The functional unit of compact bone
  • Lamellae arranged in concentric circles around central canal, containing ANV
  • Canniliculi diffuse nutrients through interstitial fluid to osteocytes
  • Also Volkmann canals link up Haversion canals
  • One central canal and all surrounding circles of lamellae are one osteon
  • Arranged in direction of stress
  • Interstitial lamellae fill gaps (old osteons)
25
Q

What are packets also known as?
What do they rely on?

A
  • Trabecular osteons called packets
  • Rely on diffusion from bone marrow through canaliculi
  • no need for haversian canals
26
Q

Describe Osteoclasts as bone cells

A
  • Found where bone is being resorbed, directly on the bone in resorption bays
  • Large, multinucleated, acidophilic
  • Not related to osteoblasts, formed by fusion of macrophage progenitor cells
  • Ruffled border where absorption takes place
  • Clear zone forms a ring around resorption zone and seals
  • Carbonic acid decalcifies, lysosomes break down bone proteins
27
Q

How does Osteoclast activation work?

A
  • Osteoclast precursors express RANK receptor molecule
  • Reacts to RANK ligand (RANKL), from stromal cell surfaces or activated T lymphocytes (inflammation)
28
Q

How is Osteoclast activation compromised?

A
  • RANK-RANKL pathway blocked by osteoprotegerin (OPG)
  • Produced by osteoblasts, regulated by many bone metabolic regulators
  • Therefore, little osteoclasts when new bone being made
  • OPG/RANKL system mediates bone resorption/remodelling
29
Q

What is the theory about bone remodelling?

A
  • Dynamically changing organ, small portions constantly being remodelled
  • Every 7 year, whole skeleton replaced. Process called bone remodelling
30
Q

Watch lecture to view how bone remodelling takes place

A
31
Q

What are the 2 different types of bone formation?

A
  • Intramembranous ossification
  • Endochondral Ossification
32
Q

What is the Intramembraneous ossification method of bone formation?

A

Intramembraneous ossification
- Simple method, bone forms straight from mesenchyme
- Flat bones of skull and face, mandible, clavicle

33
Q

What is the endochondral ossification method of bone formation?

A
  • Uses cartilage precursor as a framework
  • Axial and weight bearing bones
  • Only refers to initial setting down of bone
  • Remodelling by appositional growth
  • Long bones later use intramembranous as well
34
Q

Describe Intramembraneous ossification in more detail (Part 1)

A
  • Within embryonic connective tissue precursor, the mesenchyme
  • Ossification centre appears, aggraegation of osteoprogenitors
  • Osteoblasts accumulate at periphery, produce ostoid inwards, trapping osteocytes
35
Q

Describe Intramembraneous ossification in more detail (Part 2)

A
  • Forms woven bone, in two plates (outer and inner) with thick trabeculae
  • Spaces lined with osteoblasts and endothelial cells
  • Woven bone eventually replaced by lamellar bone. Blood vessels carry bone marrow cells to spaces between trabeculae
36
Q

Describe Endochondral Ossification in a bit more detail

A
  • Mesenchymal cells differentiate into chondrocytes
  • Produce hyaline cartilage model of bone
37
Q

Describe what occurs during Endochondral Ossification bone formation (PART 1)

A
  • Cuff of bone forms (around diaphysis in long bone)
  • Chondrocytes continue to grow and mature (zone of hypertrophy)
  • Chondrocytes in midregion become hypertrophic, then synthesise TNAP
  • Causes calcification of cartilage to occur (not mineralisation)
  • Calcified cartilage matrix inhibits diffusion, chondrocytes die off
38
Q

Describe what occurs during Endochondral Ossification bone formation (PART 2)

A
  • Calcified cartilage matrix inhibits diffusion, chondrocytes die off (zone of calcified cartilage)
  • Osteoprogenitor cells and blood vessels from periosteum invade, proliferate and differentiate into osteoblasts, which start to lay down bone matrix (resorbtion zone).
39
Q

Describe what occurs during Endochondral Ossification bone formation (PART 3)

A
  • Secondary ossification centres form after birth in epiphysis
  • Continues until only physis (growth plate) is left of original cartilage framework
  • New cartilage produced (zone of proliferation) and resorbed (zoned od resorption) to grow bone
  • Plate maintained until maximal growth achieved, then epiphysial closure takes place (epiphyseal and diaphyseal marrow cavities become confluent)

SGUL - Physiology 2 (37 decks)

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