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1. Describe bone physiology and the bone remodeling cycle.
Transcript of 1. Describe bone physiology and the bone remodeling cycle.
Marissa, Jeremy and
University at Buffalo
State University of New York
1. Describe bone physiology and the bone remodeling cycle. Be sure to emphasize the two types of bone tissue and the roles of osteoblasts and osteoclasts.
Bone is living, growing tissue that is continuously remodeling itself. Bone is composed largely of a
mineral matrix of calcium and phosphate salts as well as collagen fibers and water
. Calcium is essential for maintaining the necessary level of bone mass to
support the structures of the body. The body is constantly using calcium for the heart, blood, muscles and nerves.
Calcium is also lost through normal bodily processes such as waste and the shedding of hair, fingernails, sweat and skin
The process of bone remodeling occurs through the actions of osteoclasts and osteoblasts.
Osteoclasts are cells that remove old bone, and this process is called bone resorption
Osteoblasts are cells that then refill the bone cavities with new bone, and they are also responsible for bone mineralization/calcification
Bone remodeling occurs rapidly in childhood, where rate of formation exceeds absorption.
2. Explain the relationship between calcium and bones.
Calcium is vital to the strength of bones.Almost
99 percent of the body's calcium is stored in the bones
. Thus, bones serve as calcium reservoirs for the body. Calcium
affect bone strength and can cause bone loss to worsen
. Calcium needs are greatest in childhood and adolescence. With older age comes a decreased efficiency in absorbing calcium, so it's important to consume enough calcium as one gets older.
3. Explain how the body controls calcium levels in the bones and blood. Be sure to describe the roles of parathyroid hormone (PTH) and calcitonin in detail.
• Rising blood Ca 2+ levels trigger the thyroid to release calcitonin.
• Calcitonin stimulates calcium salt deposit in bone
• Falling blood Ca 2+ levels signal the parathyroid glands to release PTH.
• PTH signals osteoclasts to degrade bone matrix and release Ca 2+ into the blood.
4. Explain specifically how osteoporosis affects the bone matrix and the normal bone remodeling cycle.
In osteoporosis, the
net rate of bone resorption exceeds the rate of bone formation
, resulting in a decrease in bone mass. More specifically, an imbalance in this process will lead to brittle bones or osteoporosis. The increased porosity of the matrix makes the bone less elastic and stable and increases the risk of fracture.
1. Define "perimenopausal."
Perimenopause, or menopause transition, begins
several years before
menopause. It's the time
when the ovaries gradually begin to make less estrogen
. It usually starts in a woman's 40s, but can start in her 30s or even earlier.
Perimenopause lasts up until menopause,
the point when the ovaries stop releasing eggs
. In the last 1 to 2 years of perimenopause, this drop in estrogen speeds up. At this stage, many women have menopause symptoms.
2. Explain how menopause affects a woman's hormonal levels
Ovaries are the source of
estrogen and progesterone
, the two key hormones that control the reproductive system, including the menstrual cycle and fertility in women. Women are born with all the eggs you will ever have. The eggs are in the follicles, which are found in the ovaries. During
, the number of
ovarian follicles declines and the ovaries become less responsive
to the two other hormones involved in reproduction—
Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH)
. As your ovaries age and release fewer hormones, FSH and LH can no longer perform their usual functions to regulate your estrogen, progesterone and testosterone. These inevitable changes in your hormones and natural
decline of estrogen and progesteron
levels during menopause can significantly affect your health for years to come.
3. Explain how estrogen affects calcium levels in bones.
Estrogen has a significant effect on bone health.
Estrogen retards the bone resorbing effects of PTH
and has been shown to decrease bone loss. Estrogen
helps to deactivate osteoclastic
maintain normal rates of bone formation
that occurs with menopause causes a net
increased rate of bone resorption, and thus a loss of bone density
. This occurs because a lack of estrogen causes osteoclast population explosions and increased osteoclast life spans and it decreases the estrogen-receptor signaling on osteoblasts, thus decreasing their productivity. Estrogen deficiency can thus lead to excess loss of calcium from bones.
4. Explain how smoking affects estrogen levels. How does this in turn affect calcium levels?
Smokers have lower levels of estrogen compared to nonsmokers. Thus, they experience the bone health risks associated with estrogen deficiencies. Smoking also may decrease calcium absorption from one's diet.
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