Bone structure and function

 

Power point presentation for FRCS basic science course (click here) Be patient 12mb

Function

    1. Mechanical role

    2. Ionic reservoir

    3. Haemopoietic reservoir

 

Structure

Cells 10 %

(Functional)

 1. Osteoclasts
2. Osteoblasts
3. Osteocytes
4. Bone lining cells
   
   

Matrix 90%

(Structural)

 1. Organic 40%
2. Inorganic 60%

 

Cells (10%)

  1. Osteoclasts

  2. Osteoblasts

  3. Osteocytes

  4. Bone lining cells

1. Osteoclasts

Multinucleate giant cells of haemopoetic origin (monocyte progenitors)

Resorb bone

Resorb bone by forming howships lacunae, Integrins attach to bone sealing the space, produce H+ via carbonic anhydrase lowering the PH increasing solubility of hydroxyapatite. Organic matrix resorbed by proteolysis.

 

2. Osteoblasts

Osteoblasts form bone.

Undifferentiated mesenchymal cells, line bone surfaces.

Osteblasts affected by several things:

  • IL

  • PDGF

  • IDGF

  • PTH

  • 1.25 Dihydroxy Vit D

  • Glucocorticoids

  • Oestrogen

3. Osteocytes

90% of cells, osteoblasts trapped in the matrix

Maintain bone, control extracellular Ca2+ and P

Stimulated by Calcitonin, Inhibited by PTH

 

4. Bone lining cells

Bone lining cells are made from osteoblasts along the surface of  bones. Bone-lining cells are thought to regulate the movement of Ca2+ and P into and out of the bone.
 

Matrix

  1. Organic (40% of matrix)

  2. Inorganic 60% of matrix)

1. Organic (40%)

Collagens (90%) - Collagen in bONEone type ONE, polypeptide triple helix, tropocolagen bond together to form fibrils.

Proteoglycans

Non collagenous matrix proteins

    Glycoproteins

    Phospholipids

    Phosphoproteins

Growth factors

Cytokines

 

2. Inorganic (60%)

Most Hydroxyapatite (Ca10(PO4)6(OH)2)

 

Microscopic structure

  1. Primary Immature Woven

  2. Secondary Mature Lamellar

1. Primary Immature Woven

Location

    Embryonic skeleton

    Neonatal skeleton

    Growing metaphysis in under 4 yr olds

    Near sutures of skull

    In tooth sockets

    Some tendon insertions

    Callus

Properties

    Isotropic - uniform physical properties in all directions

    Soft

    Flexible

    Rapid deposition/ turnover

    High No of cells

 

2. Secondary Mature Lamellar bone

Location

    Throughout adult skeleton

Properties

    Anisotropic - properties differ based on the direction that is measured

    Hard

    Rigid

    Slow deposition/ turnover

    Low No. of cells

 

Macroscopic structure of Secondary lamellar bone

May be Cortical or Cancellous, (Note Woven bone has no particular macroscopic structure.)

 

Cortical bone

    80% of adult skeleton

    20 times stiffer than cancellous bone

    Lamellae in concentric rings aligned with lines of force

    Complex arrangement of canals (Haversian system)

 

Cancellous bone

    20% of adult skeleton

    20 times less stiff than cortical bone

    Lamellae also present aligned with lines of force

    No Haversian system

 

Bone  blood supply

Receives 5-10% of Cardiac output

3 sources blood supply

  1. Endosteal (Nutrient artery)

  2. Periosteal

  3. Metaphyseal epiphyseal system

 

1. Endosteal (Nutrient artery)

Nutrient artery enters diaphysis pierces through to medullary cavity sends ascending and descending arterioles. Centrifugal high pressure supplies inner 2/3rds

 

2. Periosteal

Low pressure on periosteum, supplies outer 1/3rd of cortex

 

3. Metaphyseal epiphyseal system

Periarticular vascular plexus eg. geniculate arteries.

 

References

McCarthy I.; The physiology of bone blood flow: a review.; J Bone Joint Surg Am. 2006 Nov;88 Suppl 3:4-9
 

Page created by: Lee Van Rensburg
Last updated: 11/09/2015