Physiology of Bone Remodeling Outcomes 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

Technical Requirements Flash Player Can be downloaded for free at the following URL http://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=shockwaveFlash

Types of Bone Cells Osteocytes Osteoclasts 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 Sequence Video courtesy of Dr Susan Ott, from website: http://courses.washington.edu/bonephys/opmovies.html Click on me if you cannot get this video to play in PowerPoint:

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 Click on me if you cannot get this video to play in PowerPoint:

Estrogen Deficient Bone Turnover Click on 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: Factors you can 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; 1989:179-213)

Bone Density Decreases in Men and Women (expressed as percent control of peak bone mass) Gambert SR, Schultz BM, Hamdy RC.  Osteoporosis:  clinical features, prevention, and treatment.  Endocrinol Metab Clin North Am.  1995;    24:317-71

Thinking Question Can men develop osteoporosis? 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 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? What hormone would you want to use to treat an osteoporotic patient?