Allen Emily Project

7/29/2019 Allen Emily Project

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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=shockwaveFlash


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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.swf


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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:

http://courses.washington.edu/bonephys/Gallery/movies/newBMUbu.swfhttp://courses.washington.edu/bonephys/Gallery/movies/newBMUbu.swf


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Estrogen Deficient Bone

TurnoverClick on me to watch video athttp://courses.washington.edu/bonephys/Gallery/movies/lilmenopause.gif

http://courses.washington.edu/bonephys/Gallery/movies/lilmenopause.gifhttp://courses.washington.edu/bonephys/Gallery/movies/lilmenopause.gifhttp://courses.washington.edu/bonephys/Gallery/movies/lilmenopause.gif


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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

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