Bone Part 2 Cholesterol UV light Vit D3 liver 25 OH D3 kidney 1 25 OH 2D3 cholecalciferol calcidiol Calcidiol major form found in blood Calcitriol active hormone calcitriol Functions of Vitamin D regulates calcium and phosphorus functions of calcium nonosseous functions not relating to bone osseous Calcium Functions Non osseous 1 enzyme activations blood clotting muscle contraction requires mg nerve impulses hormones Osseous 99 bone formation calcium activates protein kinase C which is involved in phosphorylating enzymes to activate or inactivate metabolic pathways Functions of Phosphorus skeletal energy ATP Phosphorylase reactions therefore controlling enzyme activities How does Vitamin D maintain calcium transcaltachia increased intestinal calcium abs or transcellular calcium flux that occurs as a result of calcitriol binding to intestinal membranes trans across cal calcium tachia rapidly intestine increase Ca absorption osteoblasts increase Ca to bone from blood skeletal muscle increase Ca muscle from blood How does Vitamin D calcitriol maintain calcium with Parathyroid hormone PTH stimulates parathyroid gland to stimulate PTH low serum Ca stimulates PTH which stimulate 1 hydroxylase which converts calcidiol to calcitriol Three main target tissues 1 intestine 2 bone 3 kidney Intestine Intestinal absorption of calcium increased synthesis of CaBP calbindin will increase Ca absorption calcitriol acts as a steroid hormone to stimulate transcription of mRNA s for CaBP changes to brush border increases Ca absorption transcaltachic response rapid increase in Ca absorption via endocytosis Intestinal absorption of phosphorus by increasing activity of alkaline phosphatase calcitriol increase enzyme activity therefore increase absorption Bone resorption Kidney reabsorption calcitriol stimulates reabsorption of calcium and phosphorus from bone calcitriol stimulates calcium reabsorption in the distal renal tubules of the kidneys Low Blood Calcium stimulates PTH and activates 1 hydroxylase in kidney to convert calcidiol to calcitriol which acts by itself or in combination with PTH to increase calcium reabsorption in kidneys to increase calcium blood levels also breaks down bone so calcium and phosphorus come into blood in intestines stimulating calcium absorption To Raise Blood Calcium low serum calcium signals parathyroid gland to secrete PTH PTH signals Kidney Bone Calcitriol 1 Calcidol calcitriol 2 Reabsorptionof calcium 1 Stimulates reabsorption of bone 1 Intestine increase absorption 2 Bone resorption of bone To Decrease Blood Calcium high blood calcium calcitonin signals thyroid gland to secrete calcitonin 1 Kidney decreases 1 hydroxylase decreases reabsorption 2 Bone stimulates osteoblasts inhibits osteoclasts Functions of Vitamin D regulates calcium and phosphorus functions of calcium nonosseous osseous Nonosseous Function insulin secretion thyroid hormone synthesis proliferation and differentiation of immune cells Treatment of psoriasis inhibits proliferation of keratinocytes enhances differentiation of epidermis Vitamin D Deficiency Children Ricketts failure of bone to mineralize epiphyseal cartilage grows but no bone matrix long bones of legs will bow in or out spinal pelvic and thoracic deformities Adults Osteomalacia vitamin D deficiency decrease calcium absorption decline in serum calcium increase PTH PTH promotes bone resorption Bone matrix is spared but remineralization is impaired results in bone pain and soft bones poor dietary intake more time spent indoors impaired synthesis of cholecalciferol in skin and reduced activity of 1 hydroxylase Risk for Deficiency Elderly climate skin pigmentation fat malabsorption renal disease breastfed infants decreased renal activity decreased 1 hydroxylase American academy of pediatrics supplement 400 IU Treatment Vitamin D supplements Toxicity overexposure to sun excessive dietary intake general symptoms include nausea vomiting diarrhea weakness headache severe symptoms hypertension renal dysfunction calcification of soft tissues kidney heart lungs blood vessels Calcium Absorption Small Intestine calbindin transport protein saturable requires energy and magnesium regulated by vitamin D occurs in duodenum and proximal jejunum Paracellular passive primarily in jejeunum and ileum occurs between cells rather than throught them Large intestine passive Calcium deficiency Rickets secondary to vitamin D deficiency Tetany intermittent muscle contractions that fail to relax especially of the arms and legs muscle pain numbness and spasms Osteoporosis Type 1 postmenopausal women 50 65 yrs Type II men and women over 70 vertebrae hips pelvis long bones demineralization of cortical and trabecular bone loss of trabecular bone in vertebrae and distal radius due to loss of estrogen Calcium Toxicity Hypercalcemia increase of calcium levels in blood that can lead to deposition of calcium in soft tissues Constipation increased risk of kidney stones Anorexia muscle weakness spasms hallucinations personality changes changes in cardiovascular and neuromuscular function will usually see with hypokalemia hypocalcemia low vit D levels Magnesium Function used in over 300 enzyme reactions as a structural cofactor or as an allosteric activator of enzyme activity glycolysis hexokinase PFK Krebs cycle decarboxylation HMP shunt transketolase beta oxidation required for initiation for acetyl coA synthetase macronutrient metabolism energy production magnesium provides stability to ATP Deficiency hypomagnesemia symptoms At risk renal disease diabetes excessive alcohol refeeding syndrome parathyroid disease Toxicity excessive intake will not cause toxicity except in causes of renal failure high levels of Mg salts can cause diarrhea and dehydration acute toxicity muscular paralysis cardiac and or respiratory failure Phosphorus Functions skeletal tissue and formation of bone laid down on collagen to form bone High phosphorus low calcium hyperparathyroidism PTH increases bone reabsorption Functions 1 Skeletal laid down on collagen to form bone where most of body s P is found 2 Structural cell membranes phospholipids 3 DNA and RNA Energy 4 high energy phosphate bonds 5 creatine phosphate 6 Second messengers cAMP glycogenolysis glycogenesis 7 Enzyme regulation phosphorylase reaction Phosphorus excretion urine 67 90 high P intake increased urinary excretion feces Deficiency rare anorexia bone loss muscle weakness cardiac dysfunction At risk malnourished refeeding syndrome aka
View Full Document
Unlocking...