Metabolism 2 Study Guide 3 Farrel Bone 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 On the 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 by secreting 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 the bone 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 The main 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 out that 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 activity is 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 Phosphorus is 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 serum level of calcium and it does this by acting on the osteoblasts to release RANKL which will turn on the osteoclasts to break down bone to release the calcium into the blood stream 6 Explain everything about bone remodeling Bone is constantly being broken
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