MLAB 2401: Clinical ChemistryKeri Brophy-Martinez

Overview:Mineral and Bone Metabolism

Calcium Homeostasis Organs involved

◦Small intestine◦Skeleton

Hydroxyapatite ( calcium+ phosphorus+ hydroxide)

◦KidneysOrigin

◦DietReservoir

◦Bone

Forms of CalciumBound to albumin–45%

◦Reversible process◦Binding is pH dependent

Free “ionized”–50%Complexes with anions -5%

Ionized CalciumFree calcium in bloodTightly regulatedBiologically active formAdvantage

◦Not associated with proteins or anions

Functions of CalciumNerve impulse transmissionCofactor in certain enzymesCoagulation of bloodSkeletal mineralizationPreservation of cell membrane

integrity and permeability

Regulation of Calcium Homeostasis

Parathyroid hormone- PTHVitamin D3

Calcitonin

Parathyroid Hormone- PTHOriginates from the parathyroid glandSecretion 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

Regulation of Calcium Homeostasis

Vitamin D3/ CholecalciferolSynthesis occurs in skin, liver, kidneysAffects gut, bone, and parathyroidActions/ 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

Vitamin D: Where Does it Come From?Sources of:

◦ Diet Animal tissues and products ( liver) Irradiated milk

◦ Sunlight

CalcitoninSecreted by the thyroid glandSecreted when blood calcium rises

Inhibits PTH and Vitamin DInhibits bone resorption,

promotes bone formation

PhosphorousOrigin

◦Diet◦Bone◦Phosphate ion is distributed equally.

Intracellular Component of macromolecules

ExtracellularInverse relationship with Calcium

Functions of PhosphorousComponent of bones & teethEssential part of cell membranesContributes to enzyme functionStorage and transfer of energyComponent of many compounds

Phosphorous RegulationKidneys

◦Excrete or reabsorbOther factors

◦PTH Increases renal excretion

◦Vitamin D increases levels Phosphate absorption in intestine Phosphate reabsorption in kidneys

◦Growth Hormone, calcitonin, acid-base status

Magnesium2nd most abundant intracellular

cationLocation

◦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

Forms of MagnesiumFree or ionized (~55%)Bound to proteins (~30%)Complexed with phosphate,

citrate and other ions (~15%)

Functions of MagnesiumImportant co-factor in reactions

using ATP◦Carbohydrate metabolism◦Muscle contraction◦Blood coagulation

Membrane stabilizationNerve conductionMaintenance of potassium

Magnesium RegulationPrimary regulatory factor

◦Amount of magnesium in the plasmaRegulatory control

◦Kidney Excrete or reabsorb magnesium

depending on condition◦Parathyroid hormone Increases renal reabsorption Enhances absorption in intestines

ReferencesBishop, 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/vita

min-d-cold-flu-correlation.htmlSunheimer, R., & Graves, L. (2010). Clinical

Laboratory Chemistry. Upper Saddle River: Pearson .