Calcium
د- هديل فاضل فرهود
@Introduction:
Ca constitute 1.5-2% of total body wt & 39% of body minerals. The body of healthy humans cotains about 1250 g , About 99% of which is presented in bones & teeth as deposits of ca phosphate & ca hydroxide.
The remaining 1% is found in extracellular fluid, soft tissue & as component of various membrane structure.
@Food sources:
*milk & diary products are the best source.
*leafly green vegetables such as turnip greens & kale are important sources of ca *beans , shellfish & fish of the sardine & canned salmon with the bone,
*meet & cereal green are poor sources .
*Numerous calcium-fortified foods are available, including soy milk, soy yogurt, and soy cheese, as well as calcium precipitated tofu and calcium-fortified cereals, breakfast bars, pastas, waffles, and juices . Calcium bioavailability in most of these sources is equivalent to that of milk. As an example, one 8-ounce (240 mL) glass of calcium-fortified orange juice provides 300 mg of calcium, equivalent to an 8-ounce glass of milk. The fractional absorption of calcium from calcium-fortified breakfast cereal was equivalent to that of milk .
@Absorption of Ca:
Most of the ca absorbed in the proximal small intestine usually 20-30 % of ingested ca.
Factors increase ca absorption:*
1- increase need: growth, pregnancy, lactation, exercise, ca deficiency.
2- vit D.
3- hydrochloric acid in the stomach (ca salt are more soluble in acid than in basic solution.
4- lactose: milk sugar lactose has beneficial effect on ca absorption.
*Factors decrease ca absorption:
1- vit D deficiency.
2- oxalate, phytate, fiber.
3-excessive GI motility, laxative, antacids.
4- antibiotics as penicillin, tetracycline.
5- aging.
@Excretion of Ca:
175 mg in the urine , 125 mg in the feces & 20 mg from the skin. Excretion is increased in high protein diet, postmenopausal women, intake of caffeine & theophylline , prolong immobilization, alcohol, cigarret smoking, drugs such as CS , diuretics.
@Function of Ca:
1- ca is principle component of the skeleton & provide the strength & rigidity of skeleton & teeth.
2- increase perimability of cell membrane(tranismission of ions across the membrane like Na, K, Cl).
3- activate a number of enzymes including pancreatic lipase, adenosine triphosphate & protiolytic enzymes.
4- regulate the contraction & relaxation of muscles including the heart beat, & for tranismission of nerve impulse.
5- catalyse two steps in clooting blood.
6- aids in absorption of vit B12 from the illum.
7- intracellular ca has many important function including glycogen breakdown, muscle contraction, hormone secretion & cell division.
@Ca requirement:
Adults ------------------------800mg/day.
Infant(up to 1 year)--------400-600 mg/day.
Children(1-10 years)-------800 mg/day.
11-18 years-------------------1200mg/day.
Pregnant & lactating-------1200mg/day.
@Results of ca deficiency:
a- bone deformity (osteomalacia, osteoporosis, rickets)
b- tetany & muscle cramp.
c- Osteopenia of prematurity
Osteoporosis
A disease characterized by a low bone mass & micro-architectural deterioration of bone tissue, leading to enhance fragility & a consequent increase in fracture risk . it classify into :
* primary :which is divided into : type I : postmenopausal osteoporosis ( in women within 15-20 years of menopausal without estrogen )
Type II : age associated senile osteoporosis ( around age 70 )
Secondary : result from disease process ( parathyroid disease , CRF ,chronic diarrhea , hyperthyroidism ) or from certain drugs ( phenytoin , phenobarbiton , thyroid hormone , corticosteroids , tetracycline )
Risk factors for osteoporosis :
1- age > 60 years.
2- race (white > black), female > male.
3- low body wt. < 58 kg.
4- endocrine diseases like DM, pituitary disease, thyrotoxicosis & hyperparathyroidism.
5- low ca intake for long time.
6- estrogen depletion( early menopause)
7- smoking, alcoholism, physical inactivity, excessive caffeine intake, excess fibers.
8- personal history of fracture in adult & genetic factors (there appears to be evidence for strong heredity role in the development of bone mass by the age of 25 years that is independent of the consumption patterns of ca & other minerals.
9- inflammatory disease: ankylosing spondylitis, rheumatoid arthritis & inflammatory bowel disease.
10- GI diseases: malabsorption, chronic liver disease.
11- drugs: CS , anticonvulsants.
Prevention & treatment :
1- increased intake of ca by diet & supplementation , increased vit D intake.
2- estrogen replacement most effective when use in 1st 5-8 years within menopause.
3-encorregment of exercise
4- reduce the likelihood of factors associated with bone loss(smoking, alcohol abuse, certain drugs).
Osteomalacia
Characterized by failure to maintain bone matrix & reduce in mineral content of bone & softening of bone & deformity mainly in limbs, spines, thorax, pelvis, on X-ray pseudo fractures (looser s zone) is seen, general aches & sometimes fractures following minimal trauma.
Its associated with concurrent lack of vit D & imbalance of ca & phosphorous intake.
Most often observed in female at childbearing age with depleted ca due to repeated pregnancies with low intake of ca or in female with inadequate exposure for sun light or in elderly.
Rickets
Associated with malformation of bone because of deficient mineralization of organic matrix . vit D is specific for prevention of rickets.
Tetany
Extreme low level of ca in the blood & increase irritability of nerve fibers & cause muscle cramps.
OSTEOPENIA OF PREMATURITY —
Osteopenia of prematurely, also called metabolic bone disease of prematurely, is defined as postnatal bone mineralization that is less than intrauterine bone density at a comparable gestational age . Osteopenia occurs commonly in preterm infants; the incidence and severity increase with decreasing birth weight . Characteristic radiographic changes are seen in 55 percent of infants with birth weight <1000 g . High bone turnover appears to be more important than decreased bone formation in the pathogenesis of this disorder .
In addition to immaturity, the major predisposing factor is deficiency of Ca and P because of inadequate intake. Other risk factors include prolonged parenteral nutrition and medications that affect mineral metabolism, such as caffeine, loop diuretics, and corticosteroids . Decreased bone mineralization also occurs in infants who are small-for-gestational age or are born to diabetic mothers
Clinical features — Osteopenia typically develops in premature infants at three to 12 weeks of age. The condition is not clinically apparent and is detected by routine laboratory monitoring.