Metabolism 2 Study Guide 3Bone Health 1. What are the cell types that we need to know for the bones?- Bone is divided into two class, depending on its composition. There is trabecular bone and cortical bone. These are the two classes of bone, but the bone cells are of more importance. To understand osteoblasts and osteoclasts, which is the next cell, we have to review that bone is continuously being remodeled in the body. What this means is that, even as you read this, certain cells are breaking down your bone. Why would this ever be beneficial? Bone is always being rebuilt, so after bone breakdown (called resorption) bone is rebuilt. The first cell is called osteoblasts, which is made in the bone marrow. This are the cells responsible for rebuilding the bone after it is resorped (think Blasts-Build bone). They do this by responding to calcitonin—this is the hormone has the responsibility of lowering blood calcium. The blood calcium will enter the matrix of the bone and this is how blood calcium is lowered. Onthe other end, parathyroid hormone is responsible of raising blood calcium, so when this hormone is present, osteoblast action will decrease—because to raise blood calcium, the calcium is released from the bone. Calcitriol is the active form of vitamin D that also works to raise blood calcium level. It tells the osteoblasts to release a compound called RANKL, which will then signal osteoclasts to get to work. This is the next cell to talk about. Osteoclasts are the bone breakdown cells. These cells are large and nucleated and they work bysecreting lysosomes (highly acidic cells that destroy other cells/debris), and proteases to breakdown the protein. Parathyroid hormone or PTH signal this cell to work and break down thebone the release calcium into the blood stream. So the main purpose of the PTH is to raise the blood level of calcium. Calicitriol also acts by telling the osteoblasts to release RANKL, and this tells the osteoclasts to get to work. Osteocytes are the bone cells (-cytes are the main cell in any system), and these form the bone membrane. They work by letting calcium, phosphorus, and magnesium enter the bone and attach to certain proteins. The calcium then makes the bone matrix—the hydroxyapatite. Themain proteins to know are collagen, osteonectin (binds to calcium and the collagen), and osteopotin (binds the hydroxyapatite that is formed and all the bone cells). So you can figure outthat the osteoblasts tell the osteocytes to work and that is how bone is formed. The other cells are the fibroblasts—make the collagen protein. The chondrocytes—make the base for the tendons and ligaments. Then the reticulocytes. 2. What is bone remodeling?- As talked about above, bone is always being broken down and rebuilt, for growth and repair. Throughout life, bone has to adapt to your body as you grow or to repair itself if you injure it. It also has to regulate you blood calcium level. You will reach your peak bone mass around early adulthood. As an adolescent, you bone activityis the greatest, as you are growing the most in this stage. Since bone activity is the greatest, this is the period that you build bone density---so be active these years! The denser the bone gets during this period, the slower it will degrade when it starts to break down in later life. For women, bone loss is accelerated of menopause - Some factors that affect bone mass are: Activity as you guessed. Protein intake, as collagen etc is protein Sodium intake Smoking is bad for everything Alcohol unfortunately Calcium intake (Duh)3. What is the DRI for all the minerals involved in bone health and where are they found?- Multiple minerals and one vitamin is involved in bone health—calcium, phosphorus, magnesium, and vitamin D. Men and women need 1000 ug/day in early adulthood (age 19-30). As they are growing, they need more for the increased bone activity; so 1300 ug/day at age 9-18. After age 50 when they start to lose bone density, they still need a greater amount at around 1200 ug/day. Vitamin D is constant at 5000 IU, except once they past age 50. Then it doubles to 10000 IU. We always want to maintain bone density, thus the increases when bone starts to dergrade. Phosphorus is constant at 700 ug/day, except when growing. Then it is 1250 ug/day Magnesium is greater for men in adulthood, ranges when growing, and greater past age 50.- Calcium, as we know, is found in dairy products, vegetables, some seafood, and in foods it is fortified in. There are three forms that is can be supplemented as: calcium citrate (around 35%) calcium monophosphate (around 25%) and calcium carbonate (around 40%). - Phosphorus is mostly found in its organic form in meat and poultry, and dairy. In plants, it is inorganic. - Magnesium is widespread in coffee, nuts, and veggies. - Vitamin D is in beef, dairy, made via sunlight, fish, and plants. This is just memorization of all the sources.4. What is important about vitamin D and its structures?- Vitamin D has different forms, but we only care about the D3 form.- There are the ergocalciferol form and the cholecalciferol form; D2 and D3. D2 is the form that is in plants and what is commercially available BUT this is not the active form. In plants, sterols act with irradiation to form D2 D3 is the active form and is found in animal products. It is made via cholesterol in the body.o In order to get to the active form, cholesterol acts with uv light (this is how sunlight forms vitamin D, so we need cholesterol) and it forms D3 (remember this is cholecalciferol!)o Once the cholecalciferol is formed, it will form calcidiol in the liver. Then the calcidiol will travel to the kidney to form 1-hydroxylase briefly and then calcitriol. Calcitriol is the product that we want and it is the active form of vitamin D. 5. What does vitamin D do and how does it work?- Vitamin D is used to maintain calcium and phosphorus levels in the body. Calcium has the function in blood clotting and muscle contraction (this is beyond its role in bone formation). If we remember back to muscle contraction with the sarcomeres and such, calcium is required to even start the process of contraction. These functions are called the non-osseous functions. Phosphorusis also involved in the bone health; it is the only major ion along with calcium. - Now for how calcitriol, the active vitamin D works: Calcitriol is used to increase the
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