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Physiology of Bone Remodeling
Outcomes1. Compare and contrast the function of osteoblasts and
osteoclasts during bone growth, repair, and remodeling.
2. Explain the roles of calcitonin, parathyroid hormone andcalcitriol in bone remodeling and blood calcium regulation.
3. Contrast the remodeling processes ofa child (birth toadolescence) and an adult (middle to old age).
From: HAPS learning Outcomes Module F
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Technical Requirements
Flash Player
Can be downloaded for free at the following
URL
http://www.adobe.com/shockwave/download/
download.cgi?P1_Prod_Version=shockwaveF
lash
http://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=shockwaveFlashhttp://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=shockwaveFlashhttp://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=shockwaveFlashhttp://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=shockwaveFlashhttp://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=shockwaveFlashhttp://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=shockwaveFlash7/29/2019 Allen Emily Project
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Types of Bone Cells
Osteocytes Sense mechanical strain, to direct osteoclast and
osteoblast activity
Derived from osteoblasts that develop into osteocytes
while the bone is being formed Are connected to each other through long fingerlike
extensions
Osteoclasts Dissolve and resorb bone
Large multi-nucleated cells
Derived from bone marrow and related to white bloodcells
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Types of Bone Cells Cont.
Osteoblasts Refill cavity from osteoclast with secretion called
osteoid
Catalyze the mineralization of osteoid
Become lining cells when finished filling a cavity
Derived from bone marrow and related to structuralcells
Lining Cells Cover bone not undergoing bone remodeling
Regulate movement of calcium into and out of bone
Removal of these cells necessary for osteoclasts toresorb bone
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Bone RemodelingOsteoblast
Osteoclast
Lining Cell
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Bone Remodeling Sequence
Click on me if you cannot get this video to play in PowerPoint:
Video courtesy of Dr Susan Ott, from website: http://courses.washington.edu/bonephys/opmovies.html
http://courses.washington.edu/bonephys/Gallery/movies/newBMUbu.swfhttp://courses.washington.edu/bonephys/Gallery/movies/newBMUbu.swf7/29/2019 Allen Emily Project
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Photo courtesy of Dr Susan Ott, From: http://courses.washington.edu/bonephys/opgallery.html
So what does bone remodeling look like?
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Normal Bone Turnover
Click on me if you cannot get this video to play in PowerPoint:
Video courtesy of Dr Susan Ott, from website: http://courses.washington.edu/bonephys/opmovies.html
http://courses.washington.edu/bonephys/Gallery/movies/newBMUbu.swfhttp://courses.washington.edu/bonephys/Gallery/movies/newBMUbu.swf7/29/2019 Allen Emily Project
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Estrogen Deficient Bone
TurnoverClick on me to watch video athttp://courses.washington.edu/bonephys/Gallery/movies/lilmenopause.gif
Video courtesy of Dr Susan Ott, from website: http://courses.washington.edu/bonephys/opmovies.html
http://courses.washington.edu/bonephys/Gallery/movies/lilmenopause.gifhttp://courses.washington.edu/bonephys/Gallery/movies/lilmenopause.gifhttp://courses.washington.edu/bonephys/Gallery/movies/lilmenopause.gif7/29/2019 Allen Emily Project
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Why is bone remodeling important to study?
Osteoporosis, or porous bone, is a disease characterized bylow bone mass and structural deterioration of bone tissue,
leading to bone fragility and an increased susceptibility to
fractures especially of the hip, spine and wrist.
Reprinted from Dempster, DW et al. J Bone and Mineral Research 1986:1:15-21
Normal Bone Osteoporotic bone
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Risk Factors
Factors you cannotchange:
Gender
Age
Body Size Ethnicity
Family history
Factors you canchange:
Sex hormone levels
Anorexia
A diet low in calciumand vitamin D
Use of certain
medicines, such as
glucocorticoids or
some anticonvulsants
An inactive lifestyle
Cigarette smoking
Excessive use of
alcohol
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(Wasnich RD et al. Osteoporosis: critique and practicum. Honolulu: Banyan Press; 1989:179-
Bone Mass Changes with Age
in Females
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Gambert SR, Schultz BM, Hamdy RC. Osteoporosis: clinical features, prevention,
and treatment. Endocrinol Metab Clin North Am. 1995; 24:317-71
Bone Density Decreases in
Men and Women
(e
xpressedaspercentcontrol
of
peakbonema
ss)
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Thinking Question
Can men develop osteoporosis?
What approximate years of life are
osteoblasts most active?
See webct discussion forum for help
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Hormonal Regulation of Calcium
Why is the body so concerned about bloodcalcium levels?
Many Reasons! Calcium is very important for many cell signaling
events It is necessary for:
Nerve signaling
Coagulation Secretion by neurons and glands
Cell division
Muscle contraction
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If the blood calcium levels are low
Parathyroid gland
(located on posterior
Of thyroid gland)
Parathyroid hormone (PTH)
Osteoclasts degrade
Bone matrix
Release Calcium into the bloodstream
Raising Calcium levels
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If blood calcium levels are high
Thyroid glandCalcitonin
Stimulates Calcium deposits
In bone
Thus lowering blood calcium levels
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Calcitrol
Active form of Vitamin D
Release is stimulated by high PTH levels
and low blood calcium and phosphate
levels
Inhibits calcitonin release and increases
absorption of calcium and phosphate in
the GI tract and reabsorption of calcium in
the kidneys
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Thinking Questions
1. One problem with extended duration
space travel is that while astronauts are
in space their bone density decreases.Thinking about what you have learned
about bone cells, which cells could be
causing this bone loss?
2. What hormone would you want to use to
treat an osteoporotic patient?
See webct discussion forum for help