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MLAB 2401: Clinical Chemistry Keri Brophy -Martinez

MLAB 2401: Clinical Chemistry Keri Brophy -Martinez. Overview: Mineral and Bone Metabolism. Calcium Homeostasis . Organs involved Small intestine Skeleton Hydroxyapatite ( calcium+ phosphorus+ hydroxide) Kidneys Origin Diet Reservoir Bone. Forms of Calcium. Bound to albumin–45%

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MLAB 2401: Clinical Chemistry Keri Brophy -Martinez

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  1. MLAB 2401: Clinical ChemistryKeri Brophy-Martinez Overview: Mineral and Bone Metabolism

  2. Calcium Homeostasis • Organs involved • Small intestine • Skeleton • Hydroxyapatite • ( calcium+ phosphorus+ hydroxide) • Kidneys • Origin • Diet • Reservoir • Bone

  3. Forms of Calcium • Bound to albumin–45% • Reversible process • Binding is pH dependent • Free “ionized”–50% • Complexes with anions -5%

  4. Ionized Calcium • Free calcium in blood • Tightly regulated • Biologically active form • Advantage • Not associated with proteins or anions

  5. Functions of Calcium • Nerve impulse transmission • Cofactor in certain enzymes • Coagulation of blood • Skeletal mineralization • Preservation of cell membrane integrity and permeability

  6. Regulation of Calcium Homeostasis • Parathyroid hormone- PTH • Vitamin D3 • Calcitonin

  7. Parathyroid Hormone- PTH • Originates from the parathyroid gland • Secretion based on levels of free calcium • Activities/Roles • Stimulation of osteoclastic bone reabsorption and release of calcium and phosphate from bone • Stimulation of calcium reabsorption and inhibition of phosphate reabsorption from the renal tubules • Stimulation of renal production of 1,25(OH)2 vitamin D3, which increase intestinal absorption of calcium and phosphate

  8. Regulation of Calcium Homeostasis

  9. Vitamin D3/ Cholecalciferol • Synthesis occurs in skin, liver, kidneys • Affects gut, bone, and parathyroid • Actions/ Roles • Increases plasma calcium and phosphate concentration by increasing the absorption of calcium and phosphate from the gastrointestinal tract • Increases bone resorption and enhances the effects of PTH in the nephron to promote renal tubular calcium reabsorption • Stimulates osteoclasts to metabolize bone calcium

  10. Vitamin D: Where Does it Come From? • Sources of: • Diet • Animal tissues and products ( liver) • Irradiated milk • Sunlight

  11. Calcitonin • Secreted by the thyroid gland • Secreted when blood calcium rises • Inhibits PTH and Vitamin D • Inhibits bone resorption, promotes bone formation

  12. Phosphorous • Origin • Diet • Bone • Phosphate ion is distributed equally. • Intracellular • Component of macromolecules • Extracellular • Inverse relationship with Calcium

  13. Functions of Phosphorous • Component of bones & teeth • Essential part of cell membranes • Contributes to enzyme function • Storage and transfer of energy • Component of many compounds

  14. Phosphorous Regulation • Kidneys • Excrete or reabsorb • Other factors • PTH • Increases renal excretion • Vitamin D increases levels • Phosphate absorption in intestine • Phosphate reabsorption in kidneys • Growth Hormone, calcitonin, acid-base status

  15. Magnesium • 2nd most abundant intracellular cation • Location • 50-60% found in bone • 40-50% muscle & soft tissue • 1% in the RBC • Origin • Diet • Nuts, hard water, meat, green vegetables, fish, dry cereal

  16. Forms of Magnesium • Free or ionized (~55%) • Bound to proteins (~30%) • Complexed with phosphate, citrate and other ions (~15%)

  17. Functions of Magnesium • Important co-factor in reactions using ATP • Carbohydrate metabolism • Muscle contraction • Blood coagulation • Membrane stabilization • Nerve conduction • Maintenance of potassium

  18. Magnesium Regulation • Primary regulatory factor • Amount of magnesium in the plasma • Regulatory control • Kidney • Excrete or reabsorb magnesium depending on condition • Parathyroid hormone • Increases renal reabsorption • Enhances absorption in intestines

  19. References • Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry: Techniques, principles, Correlations. Baltimore: Wolters Kluwer Lippincott Williams & Wilkins. • http://rickets.stanford.edu/ • http://scrink.com/blog/wellness/2009/02/vitamin-d-cold-flu-correlation.html • Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson .

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