M edSci 4
10/8/08
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Bone
LECTURE 4 —
Structure and Function
Learning Outcomes
Outline
• Rigid for support and
transmission of forces
To be able to:
• Properties of Bone
• General structure
1.
list the names and functions
of the principal bone cells
2.
describe the events of the
principal stages of bone
formation
3.
state the origin of new bone
cells in growth and repair
4.
Outline the hormonal
regulation of serum calcium
concentration.
• Bone formation
– Roles of cells
• Bone as a calcium reservoir
• Calcium regulation (bone)
Medic al Sc ienc es Physiology 2008/09
• Rigidity conferred by
large concentration of
inorganic calcium salts in
the matrix
• Important role as calcium
reservoir.
Stanfield & Germann 21.11
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Medic al Sc ienc es Physiology 2008/09
Dr Alan Tuffery — Physiology
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Dr Alan Tuffery — Physiology
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Cells and Terminology
Bone Formation
Osteoblasts
Chondrocyte in lacuna
• Most commonly by replacement
of cartilage
– i.e. ‘intracartilaginous
ossification’
• Two processes:
• No blood vessels
• Semisolid matrix
• Little/no Ca2+ salts
1. Increase in length of the ‘bone’
• by addition of cartilage on
outside
2. Replacement of cartilage by
bone
• at epiphyseal disc.
Medic al Sc ienc es Physiology 2008/09
Dr Alan Tuffery — Physiology
• Anatomical bone
– Epiphysis — heads of the bone
– Diaphysis — shaft of the bone
www.gcarlson.com
Hyaline cartilage
• Chondrocytes — cartilage cells
• Bone cells
– Osteoblasts — immature, boneforming cells; become…
– Osteocytes — mature bone cells;
maintain bone
– Osteoclasts — break down bone
Osteoclasts
• Trabeculae/spicules — little spikes
of cartilaginous matrix/bone.
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Dr Alan Tuffery — Physiology
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M edSci 4
10/8/08
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Growth of Cartilage
Summary of Bone Formation
Ross Fig. 8.12
• Growth in length by addition of
cartilage
• Formation of bone under
periosteum (CT sheath)
• Primary ossification centre
• Bone formation at interface
• Secondary ossification centre
creates epiphyseal disc
• Removal of discs — growth
stops.
Sherwood 18-11
Medic al Sc ienc es Physiology 2008/09
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Medic al Sc ienc es Physiology 2008/09
Dr Alan Tuffery — Physiology
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Dr Alan Tuffery — Physiology
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Erosion of Bone
Bony
spicule
osteocyte
Mature (compact) Bone
• Structural units —
osteons —
• Erosion of bony spicules
by osteoclasts —
marrow
osteoblasts
osteoclast
• cylinders composed
of bony lamellae
(rings)
• large, eosinophilic (red),
multinucleate;
• Enclosed osteoblasts
are osteocytes
• Osteons are dynamic
• Central and transverse
canals contain blood
vessels and nerves.
• (Marrow cavity filled
with early blood cells).
Sherwood 19-20
Medic al Sc ienc es Physiology 2008/09
Dr Alan Tuffery — Physiology
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M edSci 4
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Remodelling of Bone
Bone and Calcium Regulation
Bone Turnover (Susan Ott, 2006)
• In bone formation
• 99% of body’s calcium is
in bone (~1 kg)
– Bone formed on
cartilaginous trabeculae
– Bony spicules eroded by
osteoclasts
– Bone added on outside
(periosteum)
– Bone removed from
inside (endosteum)
• Stable calcium-ion
concentration [Ca2+] in
interstitial fluid vital for
membrane function
Sherwood. 19-21
Ground section
• Throughout life
– Bone responds to forces
– Bone is Ca2+ reservoir.
http://courses.washington.e du/bonephys/ophome.html
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Medic al Sc ienc es Physiology 2008/09
Dr Alan Tuffery — Physiology
• Calcium-ion
concentration maintained
by balance of osteogenic
and osteoclastic activity.
Spaces (lacunae)
occupied by
osteocytes and their
processes (in
canaliculi) are filled
with carbon in
preparation
See Sherwood pp 735-740
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Medic al Sc ienc es Physiology 2008/09
Dr Alan Tuffery — Physiology
Slide 11
Bone & Calcium
Slide 12
(negative feedback loop)
Parathyroid Hormone (PTH)
Write down the item next to italics
PTH is vital
Stimulus — [Ca2+] falls
• Two Ca2+ compartments
1. Controlled variable
– Bone fluid
2. Sensor
• fast exchange — pumps
– Mineralised bone
[Ca2+]IF
3. Integrator
Sherwood. 19-21
• Slow — osteoclasts.
PTH
4. Signal
5. Effectors
2+ pumps, osteoclasts
Osteoclast
Ca
6. Compensatory response
Medic al Sc ienc es Physiology 2008/09
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Sherwood
Dr Alan Tuffery
Fig. 1-7
— Physiology
Medic al Sc ienc es Physiology 2008/09
[Ca2+]IF rises.
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Slide 13
Do not attempt to learn this!
Slide 14
Hormonal Regulation of Bone
Bone Growth
Increased growth
Vitamin D
– Promotes differentiation
of osteoblasts
Growth Hormone
– Increase osteoblast function
Decreased breakdown
Oestrogen
– Inhibits osteoclasts
Calcitonin
– Inhibits osteoclast function
(minor role in
Ca2+
Vitamin D (cholecalciferol)
An example of complex interactions
Bone Loss
Increased breakdown
Parathyroid hormone (PTH)
• A (steroid) hormone
– stimulates osteoclasts
Thyroid
absorption from gut
– Stimulates osteoclasts
• PTH increases
Vitamin A
Vitamin D activation
– Stimulates osteoclasts
Decreased growth
• Vitamin D increases
Cortisol
• Vitamin D is
activated by kidney
• PTH inhibits renal
Ca2+ reabsorption
the sensitivity of
– Osteoblast death
(apoptosis).
bone to PTH.
regulation)
Medic al Sc ienc es Physiology 2008/09
Renal Effects
• Essential for Ca2+
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Learning Outcomes — 1
Learning Outcomes — 2
To be able to :
1.
list the names and functions of the principal bone cells
•
•
•
2.
To be able to :
Osteoblasts — form bone
Osteocytes — mature bone cells (enclosed)
Osteoclasts — break down bone
3. state the origin of new bone cells in growth and repair
• Growth: ‘stem’ cells from ingrowth of CT and blood vessels
• Repair: ‘stem’ cells in the periosteum
describe the events of the principal stages of bone formation
•
Cartilage growth, erosion; bone deposition, remodelling
3.
state the origin of new bone cells in growth and repair
4.
Outline the hormonal regulation of serum calcium
concentration
Medic al Sc ienc es Physiology 2008/09
Dr Alan Tuffery — Physiology
4. Outline the hormonal regulation of serum calcium
concentration
• PTH (vital) — fall in [Ca2+], activates osteoclasts
• Calcitonin (extreme demand) — rise in [Ca2+] inhibits
ostoeoclasts.
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M edSci 4
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Fracture Repair
Remodelling
• Recall that:
http://courses.washington.e du/bonephys/ophome.html
– all CT cells are closely related
– stem cell is mesenchymal.
• Precursor cells in periosteum.
• Fracture triggers differentiation and
growth of CT and blood vessels…
• …Repair and remodelling.
Medic al Sc ienc es Physiology 2008/09
Dr Alan Tuffery — Physiology
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