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CALCIUM

CALCIUM. FCSFN 648. Introduction. Ca is the most abundant mineral in the body Ca (latin “calx” means limestone) was known as early as the first century when the Ancient Romans prepared lime as calcium oxide. Distribution & function in the body - bone . Over 99% Ca exists in the skeleton

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CALCIUM

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  1. CALCIUM FCSFN 648

  2. Introduction • Ca is the most abundant mineral in the body • Ca (latin “calx” means limestone) was known as early as the first century when the Ancient Romans prepared lime as calcium oxide

  3. Distribution & function in the body - bone • Over 99% Ca exists in the skeleton • Structural role • Functional role • Castatus can be assessed by measuring BMC by bone densitometry

  4. Distribution & function in the body - bone • Bone remodeling occurs throughout life • Bone formation is > than resorption during growth (especially adolescence)* in girls - 90% total BMC (17 y) & 99% (26 y)* boys - occurs 18.5 y • In W onset of bone loss occurs * 48 y (spine) & 37 y (femoral neck) • Maximal loss in W occurs * bet 54-58 (hips, spine etc)

  5. Distribution & function in the body - bone • On average - bone Ca pool turns over every 5-6 y • 2 types of bones * cortical* trabecular • Cortical bone

  6. Distribution & function in the body - bone • Trabecular bone

  7. Functions • Mineralization - bone & teeth • Blood clotting

  8. Functions • Other functions

  9. Solubility • Ca is absorbed only in ionized form (Ca+2) • Ca in food & dietary supplements - insoluble salts • Solubility - mildly acidic pH • Solubility doesn’t ensure better absorption • In alkaline pH, Ca may complex with minerals or other dietary components

  10. Calcium location & quantity • Average adult ~ 1 kg Ca (99% - skeleton)as calcium phosphate salts • ECF has ~ 22.5 mmol of which 9 mmol is inthe serum • Every 24 hours, 500 mmol Ca is exchanged bet bone & ECF

  11. Normal ranges • Normal serum levels (8.5-10.5 mg/dL) • Normal ionized level (4.5-5.6 mg/dL) • Amount of total calcium is dependent on albumin • Biologic effect of Ca is determined on the amount of ionized Ca rather than the total calcium

  12. Corrected Ca level • Corrected Ca level is used when albumin is abnormal • Corrected Ca (mg/dL) = measured total Ca (mg/dL) + 0.8 (4.0 - serum albumin [g/dL]), where 4.0 represents the average albumin level • With hypoalbuminemia corrected level is higher than the total Ca

  13. Absorption • Absorption - Ca has to be in the ionized form • Generally 20-50% ingested Ca is absorbed • Amount of Ca absorbed depends • Intake

  14. Absorption • Physiological factors

  15. Absorption • Occurs along the length of the small intestine • Generally 2 routes of absorption • Other route of absorption

  16. Saturable system (Transcellular) • This is active & saturable system (fig) • Takes place mainly in the duodenum & proximal jejunum • Occurs actively when Ca is in short supply (↓ dietary) • Ca moves from brush border into the enterocyte as unbound Ca+2 • Ca+2 binds with intracellular protein (calbindin or CPB) which takes Ca+2 into the mitochondria & other subcell compartments • Ca+2 leaves the enterocyte in exchange for Naor by calcium activated ATPase

  17. Saturable system (Transcellular) • Saturable process occurs

  18. Passive & Non-saturable (Paracellular) • This is passive & non-saturable system • Takes place mostly jejunum & ileum • Is dependent on vit D • Occurs passively when there is adequate dietary Ca • Ca enters into the enterocyte with the help of vit D

  19. Colon • Bacteria in the colon releases Ca bound fermentable fibers • ~ 4% (~ 8 mg/d) of dietary Ca is absorbed by this route • Amount is higher in people who are unable to absorb more Ca from the small intestine

  20. Factors that enhance Ca absorption • ↑ lactose • ↑ vit D • ↑ acidic environment • ↓ stress • Distribution of Ca intake • ↑ physiological need

  21. Absorption enhanced - lactose • From breast milk & formula • Infants fed lactose • Research - rats fed diets with differentCHOs, i.e. 25%* lactose, glucose, sucrose, maltose or starch* lactose only ↑ Ca absorption (Bergeim et al., 1926)

  22. Absorption - enhanced • Vitamin D • Acidic conditions • Lack of stress

  23. Absorption - enhanced • Distribution of Ca intake • Increased physiological need

  24. Factors that inhibit Ca absorption • Non-fermentable fibers • Phytate • Oxalate • Magnesium • Dietary fatty acids • Physical activity • Potassium

  25. Factors that inhibit Ca absorption • Non-fermentable fibers • Phytate • Oxalates

  26. Factors that inhibit Ca absorption • Magnesium • Dietary fatty acids

  27. Factors that inhibit Ca absorption • PA • Potassium

  28. Transport • In the blood, Ca is transported in 3 forms* ~ 40% Ca is bound to protein mainly albumin* ~ 10% is complexed with sulfate, phosphate or citrate* ~ 50% of Ca is found free in blood (ionized Ca+2)

  29. Storage • Skeleton is the major storage site* since ~ 99% of the body's Ca is in the bone • Short term • Long term, chronic removal of skeletal calcium

  30. Excretion • Primarily in the urine and feces • Urinary losses range from 40-200 mg/d occurs: • Urinary Ca excretion is ↓ • Urinary Ca excretion is ↑

  31. Excretion • Most Ca is filtered and reabsorbed by the kidneys

  32. Excretion • Fecal losses range from 45-100 mg/d • ↑ fecal losses are ↑ with • Skin losses 60 mg/d

  33. Regulation - calcium balance (Extracellulary) • The level of ionized calcium in plasma is controlled by 3 factors:* PTH* Calcitonin* Calcitriol (1,25-(OH)2D3 ) (i.e. vit D)

  34. Parathyroid Hormone (PTH) • ↓ in ECF (serum) Ca concentrations • PTH from the PT gland is released • PTH ↑ Ca in the ECF by* ↑ Ca absorption from the intestine (through calbindin)* mobilization of Ca from the bone via stimulation of osteoclasts* ↓ kidney excretion of Ca & ↑ renal tubular reabsorption of Ca

  35. Calcitonin • Calcitonin, is synthesized by the thyroid gland • ↑ serum Ca levels stimulates calcitonin • Calcitonin ↓ serum Ca concentration by* inhibiting osteoclast activity* prevents mobilization of Ca from bone

  36. Calcitriol (1,25-(OH)2D3 ) • Vit D enters circulation after synthesis inthe skin or consumption in the diet • Vit D is transported through the body bound to a vitamin D-binding protein • Vit D is taken to the liver, undergoes hydroxylation  forms 25(OH)D • 25 (OH)D is bound again to the bindingprotein  kidney where it is furtherhydroxylated  1,25(OH)2D3, the most active vitamin D metabolite

  37. Calcitriol (1,25-(OH)2D3 ) • In Ca deficiency, more 1,25 (OH)2D3 is produced causing enhanced* intestinal absorption of Ca* renal reabsorption of Ca* ↑ bone formation & resorption

  38. Regulation - calcium balance (Intracellulary) • Calcium Pumps* ATP dependent calcium pumps found* mitochondria * endoplasmic reticulum * nucleus * these enable movement of Ca from extracellular to intracellular fluid

  39. Interactions with other nutrients • Phosphorus • Magnesium

  40. Interactions with other nutrients • Potassium • Protein

  41. Interactions with other nutrients • Sodium • Fiber

  42. Interactions with other nutrients • Caffeine

  43. Interactions with other nutrients • Alcohol • Sodium & Protein

  44. Deficiency - Causes • Inadequate intake • Poor Ca absorption and/or excessive Ca losses • Observed

  45. Hypo - & Hypercalcemia • Hypocalcemia • Hypercalcemia • Fatal levels:

  46. Deficiency - observed • Disease states • Individuals who have ↑ need

  47. Calcium & disease prevention • Osteoporosis • 2 types of osteoporosis

  48. Calcium & disease prevention • Type I • Type II

  49. Calcium & disease prevention • Hypertension • Cardiovascular Disease • Colon Cancer

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