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osteoporosis and p. 467
osteoporosis and p. 467
osteoporosis and p. 467
for osteoporosis p. 467
osteoporosis p. 467
osteoporosis with p. 249
for osteoporosis p. 467
osteoporosis p. 467
osteoporosis p. 467
osteoporosis p. 249
osteoporosis p. 467
osteoporosis p. 467
osteoporosis p. 467
osteoporosis p. 467
bisphosphonates p. 495
corticosteroids p. 118
Cushing syndrome p. 352
denosumab p. 120
as drug reaction p. 249
estrogen p. 467
Gaucher disease p. 86
heparin p. 440
homocystinuria p. 83
hormone replacement therapy p. 674
lab values in p. 467
menopause p. 646
pituitary prolactinomas p. 333
raloxifene for p. 447, 674
teriparatide for p. 496
thiazides for p. 627
vertebral compression fractures p. 733
osteoporosis and p. 467
osteoporosis prophylaxis p. 467
Osteo- refers to bones and -porosis means pores. So, osteoporosis is when there’s a higher breakdown of bone in comparison to the formation of new bone which results in porous bones, meaning a decrease in bone density to the point of potential fracture.
Looking at a cross-section of a bone, there’s a hard-external layer known as the cortical bone and a softer internal layer of spongy bone or trabecular bone that is composed of trabeculae. The trabeculae are like a framework of beams that give structural support to the spongy bone. The cortical bone, in turn, is made up of many functional, pipe-like units called osteons, which run through the length of the bone. In the center of these osteons, there are hollow spaces called Haversian canals, which contain the blood supply and innervation for the bone cells. Around the Haversian canals, there are concentric lamellae, which look a bit like tree rings. The lamellae have an organic part, which is mostly collagen, and an inorganic part called hydroxyapatite, which is mostly calcium phosphate. In between neighboring lamellae, there are spaces called lacunae, which contain bone cells called osteocytes.
At first glance, bone may appear inert and unchanging, but it’s actually a very dynamic tissue. In fact, spongy bone is replaced every 3 to 4 years and compact bone is replaced every 10 years, in a process called bone remodeling, which has two steps: bone resorption, when specialized cells called osteoclasts break down bone, and bone formation, which is when another type of cells called osteoblasts form new bone.
Bone remodeling as a whole is highly dependent on serum calcium levels, which, in turn, are kept in the normal range by a balance between parathyroid hormone, or PTH, calcitonin and vitamin D. Parathyroid hormone is produced by the parathyroid glands in response to low serum calcium, and it increases bone resorption to release calcium into the bloodstream. On the other hand, calcitonin is produced by the thyroid gland in response to high serum calcium, so it opposes the action of PTH - therefore promoting bone formation and decreasing bone resorption. Finally, vitamin D promotes calcium absorption in the gut, so it increases serum calcium, promoting bone formation and decreasing bone resorption.
Osteoporosis refers to decreased bone density due to increased bone resorption compared to bone formation. Commonly affected bones include vertebrae, forearm, and hip. Osteoporosis is typically asymptomatic until a broken bone occurs; such breaks may occur spontaneously or with minor stress because of the disease's unremarkable progression. The treatment involves bisphosphonate drugs like alendronate and risedronate.
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