Transcript Allen-Emily-Project

Physiology of Bone Remodeling
Outcomes
1. Compare and contrast the function of osteoblasts and
osteoclasts during bone growth, repair, and remodeling.
2. Explain the roles of calcitonin, parathyroid hormone and
calcitriol in bone remodeling and blood calcium regulation.
3. Contrast the remodeling processes of a child (birth to
adolescence) and an adult (middle to old age).
From: HAPS learning Outcomes Module F
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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 blood
cells
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 structural
cells
• Lining Cells
– Cover bone not undergoing bone remodeling
– Regulate movement of calcium into and out of bone
– Removal of these cells necessary for osteoclasts to
resorb bone
Bone Remodeling
Osteoblast
Osteoclast
“Lining Cell”
Bone Remodeling Sequence
Video courtesy of Dr Susan Ott, from website: http://courses.washington.edu/bonephys/opmovies.html
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So what does bone remodeling look like?
Photo courtesy of Dr Susan Ott, From: http://courses.washington.edu/bonephys/opgallery.html
Normal Bone Turnover
Video courtesy of Dr Susan Ott, from website: http://courses.washington.edu/bonephys/opmovies.html
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Estrogen Deficient Bone
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me to watch video at
http://courses.washington.edu/bonephys/Gallery/movies/lilmenopause.gif
Video courtesy of Dr Susan Ott, from website: http://courses.washington.edu/bonephys/opmovies.html
Why is bone remodeling important to study?
Osteoporosis, or porous bone, is a disease characterized by
low 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.
Normal Bone
Osteoporotic bone
Reprinted from Dempster, DW et al. J Bone and Mineral Research 1986:
1:15-21
Risk Factors
Factors you cannot
change:
•
•
•
•
•
Gender
Age
Body Size
Ethnicity
Family history
Factors you can
change:
• Sex hormone levels
• Anorexia
• A diet low in calcium
and vitamin D
• Use of certain
medicines, such as
glucocorticoids or
some anticonvulsants
• An inactive lifestyle
• Cigarette smoking
• Excessive use of
alcohol
Bone Mass Changes with Age
in Females
(Wasnich RD et al. Osteoporosis: critique and practicum. Honolulu: Banyan Press; 1989:179-2
(expressed as percent control
of peak bone mass)
Bone Density Decreases in
Men and Women
Gambert SR, Schultz BM, Hamdy RC. Osteoporosis: clinical features, prevention,
and treatment. Endocrinol Metab Clin North Am. 1995; 24:317-71
Thinking Question
See webct discussion forum for help
• Can men develop osteoporosis?
• What approximate years of life are
osteoblasts most active?
Hormonal Regulation of Calcium
• Why is the body so concerned about blood
calcium 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
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
If blood calcium levels are high…
Thyroid gland
Calcitonin
Stimulates Calcium deposits
In bone
Thus lowering blood calcium levels
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
Thinking Questions
See webct discussion forum for help
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?