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

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

3. Forms of Calcium Bound to albumin–45% Free “ionized”–50%
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. Physiology of vitamin D in the body.
Michal L. Melamed, and Ravi I. Thadhani CJASN 2012;7:
©2012 by American Society of Nephrology

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

13. Sufficiency Of Vitamin D
Levels of vitamin D on the decline
Sun avoidance/ use of sun screen
Deficiency of vitamin D in the diet
Obesity

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

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

16. 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

17. 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

18. Magnesium 2nd most abundant intracellular cation Location Origin
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

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

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

21. 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

22. References
Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry: Techniques, principles, Correlations. Baltimore: Wolters Kluwer Lippincott Williams & Wilkins.
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Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson .