Osteoporosis Medical Background
Transcript: Medical Background Bone Structure Bone Introduction In the human body at birth, there are approximately 270 bones present; many of these fuse together during development, leaving a total of 206 separate bones in the adult, not counting numerous small Sesamoid bone. The largest bone in the body is the femur or thigh-bone, and the smallest is the stapes in the middle ear. Bone Cells Bone Cells Remodeling Remodeling Approximately 10% of the skeletal mass of an adult is remodeled each year. Bone is constantly being created and replaced in a process known as remodeling. This ongoing turnover of bone is a process of resorption followed by replacement of bone with little change in shape. Remodeling This is accomplished through osteoblasts and osteoclasts. Cells are stimulated by a variety of signals, and together referred to as a remodeling unit. The purpose of remodeling is to: 1- Regulate calcium homeostasis 2- Repair micro-damaged bones from everyday stress 3- Shape the skeleton during growth. Remodeling The action of osteoblasts and osteoclasts are controlled by a number of chemical enzymes that either promote or inhibit the activity of the bone remodeling cells, controlling the rate at which bone is made, destroyed or changed in shape. The cells also use Paracrine Signaling to control the activity of each other. For example, the rate at which osteoclasts resorb bone is inhibited by Calcitonin and Osteoprotegerin (OPG). Calcitonin is produced by parafollicular cells in the thyroid gland, and can bind to receptors on osteoclasts to directly inhibit osteoclast activity. Remodeling Osteoprotegerin is secreted by osteoblasts and is able to bind RANK-L, inhibiting osteoclast stimulation. Osteoblasts can also be stimulated to increase bone mass through increased secretion of osteoid and by inhibiting the ability of osteoclasts to break down osseous tissue. Increased secretion of osteoid is stimulated by the secretion of growth hormone by the pituitary, thyroid hormone and the sex hormones (estrogens and androgens). Remodeling These hormones also promote increased secretion of osteoprotegerin. Osteoblasts can also be induced to secrete a number of cytokines that promote reabsorption of bone by stimulating osteoclast activity and differentiation from progenitor cells. Vitamin D, Parathyroid hormone & Stimulation from osteocytes induce osteoblasts to increase secretion of RANK-ligand and interleukin 6, which cytokines then stimulate increased reabsorption of bone by osteoclasts. Remodeling These same compounds also increase secretion of macrophage colony-stimulating factor by osteoblasts, which promotes the differentiation of progenitor cells into osteoclasts, and decrease secretion of osteoprotegerin. Calcium Ca++ Calcium Ca++ Measurement in blood Calcium Foods rich in calcium include dairy products, such as yogurt and cheese, sardines, salmon, soy products, kale, and fortified breakfast cereals. Because of concerns for long-term adverse side effects, including calcification of arteries and kidney stones, both the U.S. Institute of Medicine (IOM) and the European Food Safety Authority (EFSA) set Tolerable Upper Intake Levels (ULs) for combined dietary and supplemental calcium. Calcium Bone Calcium is the most abundant mineral in the human body The average adult body contains in total approximately 1 kg, 99% in the skeleton in the form of calcium phosphate salts. Calcium From the IOM: 1- People of ages 9–18 years are not to exceed 3 g/day combined intake. 2- For ages 19–50, not to exceed 2.5 g/day. 3- For ages 51 and older, not to exceed 2 g/day. EFSA set the UL for all adults at 2.5 g/day, but decided the information for children and adolescents was not sufficient to determine ULs The body regulates calcium homeostasis with two pathways; one is signaled to turn on when blood calcium levels drop below normal and one is the pathway that is signaled to turn on when blood calcium levels are elevated The amount of calcium in blood (more specifically, in blood plasma) can be measured as total calcium, which includes both protein-bound & free calcium. In contrast, ionized calcium is a measure of free calcium. An abnormally high level of calcium in plasma is termed hypercalcemia and an abnormally low level is termed hypocalcemia, with "abnormal" generally referring to levels outside the reference range. Homeostasis Osteoporosis Osteoporosis World War II, also known as the Second World War, was a global war that lasted Osteoporosis is a disease in which bone weakening increases the risk of a broken bone. It is the most common reason for a broken bone among the elderly. Osteoporosis is defined as a bone density of 2.5 standard deviations below that of a young adult which measured by dual-energy X-ray absorptiometry (DEXA) Osteoporosis Osteoporosis Osteoporosis may be due to lower-than-normal maximum bone mass & greater-than-normal bone loss. Bone loss increases after menopause due to lower levels of estrogen. Osteoporosis may
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