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Magnesium

Magnesium. Dietary sources Daily Requirements Metabolism Important functions and Deficiency diseases. Learning Objectives. MAGNESIUM Mg At. No. 12 Atomic Mass: 24. Magnesium. MAGNESIUM. Magnesium is the 4th most abundant and important cation in humans.

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Magnesium

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  1. Magnesium

  2. Dietary sources Daily Requirements Metabolism Important functions and Deficiency diseases Learning Objectives

  3. MAGNESIUMMgAt. No. 12 Atomic Mass: 24

  4. Magnesium

  5. MAGNESIUM • Magnesium is the 4th most abundant and important cation in humans. • It is extremely essential for life and is present as intracellular ion in all living cells and tissues

  6. DIETARY SOURCES • Magnesium is widely distributed in vegetables • Found in porphyrin group of chlorophyll of vegetable cells • Found in almost all animal tissues. • Other important sources are cereals, beans, potatoes, almonds and dairy products

  7. Recommended Dietary Allowances Infants 0 – 0.5 50 mg 0.5 – 1.0 70 mg Children 1 – 3 150 mg 4 – 6 200 mg 7 – 10 250 mg

  8. Recommended Dietary Allowances AdultsMaleFemale 11 – 14 350 300 15 – 18 400 300 19 – 22 350 300 23 – 50 350 300 51+ 350 300 Pregnancy and Lactation+ 150 mg

  9. ABSORPTION • Average daily intake in humans is 250-300 mg, much of which is obtained from green vegetables. • Roughly 1/3 of dietary Mg is absorbed • Remainder is passively excreted in feces.

  10. ABSORPTION • Absorption takes place primarily in small intestine beginning within hour after ingestion • Continues at a steady rate for 2 to 8 hours • By that time 80% of total absorption has taken place .

  11. FACTORS AFFECTING ABSORPTION • Size of Mg load: Absorption is doubled when normal dietary Mg requirement is doubled and vice versa. • Dietary calcium:Increased absorption in calcium deficient diets. • Decreased absorption occurs in presence of excess of Ca. • A common transport mechanism from intestinal tract for both Ca and Mg suggested.

  12. FACTORS AFFECTING ABSORPTION • Motility and mucosal state: In hurried bowel, absorption is decreased. • Absorption decreases in damaged mucosal state. • Vit-D: helps in increased absorption. • Parathormone: increases absorption. • Growth hormone: increases absorption

  13. OTHER FACTORS: • High protein intake and Neomycin therapy increases absorption. • Fatty acids, phytates and phosphates decrease absorption.

  14. Excretion • Magnesium is lost from the body in feces, sweat and urine. 2/3rd of orally taken Mg is lost through these routes • Sweat loss: Currently it is drawing attention; 0.75 mEq of Mg is lost daily in perspiration in normal health with normal diet. Loss is much increased with visible frank sweating. • Urine: Regulation of Mg balance is principally dependant on renal handling of the ion. In a normal healthy adult with normal diet 3 to 17 mEq are excreted daily.

  15. Factors Affecting Renal Excretion • Calcium intake:Increased dietary calciumincreases excretion of Mg. • Parathormone (PTH):diminishes excretion. • Antidiuretic hormone (ADH): increases Mg excretion • Growth hormone (G.H): also increases excretion of Mg. • Aldosterone: increases excretion

  16. Factors Affecting Renal Excretion • Thyroid hormones: 80% greater excretion in hyperthyroidism. • Alcohol ingestion: oral ingestion of as little as 1.0 ml of 95% alcohol per kg, increases urinary excretion 2 to 3-fold. The increased excretion partially accounts for Mg-deficiency in chronic alcoholics with Delirium tremens. • Administration of acidifying substances (NH4Cl) is followed by increased urinary elimination of Mg.

  17. FUNCTIONS Role in Enzyme Action: • Mg is involved as a cofactor and as an activator to wide spectrum of enzyme actions. It is essential for: • Peptidases, Hexokinases,Fructokinase and PF kinase • Ribonucleases, Adenyl Cyclase, cAMP and ATP requiring enzymes, Glycolytic enzymes and • Co-carboxylation reactions.

  18. FUNCTIONS Neuromuscular Irritability: • Mg exerts an effect on neuromuscular irritability similar to that of Ca, • High levels depress nerve conduction and • Low levels may produce tetany (hypomagnasemic tetany). • Thus it helps maintain the electrical potential in nerves and muscle

  19. FUNCTIONS Constituent of Bones and Teeth: • About 70% of body magnesium is present as apatites in bones, dental enamel and dentin. • Is involved in active transport across cell membrane

  20. DISTRIBUTION • Total body Magnesium is about 20 grams. • Mainly in intracellular Fluid. • 75% complexed with Calcium in bones

  21. Distribution • Total body magnesium is approx 20 grams • Approximately 2/3rd occurs in bones • 1/3rd is in ECF and soft tissues. • Plasma level: 1.5 to 1.8 mEq/L, which is rigorously maintained within normal limits. • 15% is exchangeable

  22. Blood • Magnesium exists in blood partly bound to proteins. • Under conditions of physiological pH roughly 1/3 is “protein-bound” • The remainder 2/3rd is ionic. • C.S. Fluid: Concentration of Mg is high than in plasma.

  23. Plasma Mg in Diseases: Hypermagnaesemia: Raised values have been reported in: • Uncontrolled Diabetes mellitus • Adreno-cortical insufficiency • Hypothyroidism • Advanced renal failure, and • Acute renal failure.

  24. Plasma Mg in Diseases: Hypomagnaesemia: Low values are observed in: • Malabsorption syndrome and kwashiorkor, • Prolonged gastric suction • Hyperthyroidism • Portal cirrhosis

  25. Plasma Mg in Diseases: Hypomagnaesemia: • Prolonged use of diuretics • Chronic alcoholism • Delirium tremors • Renal diseases • Primary aldosteronism

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