Calcium
Sources
1- Milk and its products (cheese, yughert)
2- Beans, egg yolk Both Ca and P are required for bone formation and other non-skeletal functions.
Factor affecting Ca absorption
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Factor ↓ Ca absorption
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Factor ↑ Ca absorption
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1- Diet:
↑ Phosphate (in fish) , oxalate (in tomato), Phytate (in cereal) which form insoluble Ca salt
2-Alkalinity
3- Impaired fat absorption: FA form insoluble Ca soap
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1- Diet:
A- High protein diet (A.A. form soluble Ca salt, so easily absorbed)
B-↑ Lactate and citrate in lemon and orange
C- Vitamin D3
2-Acidity
3- Parathyroid hormone
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Body calcium
99 % of Ca present in bones and teeth in the form of hydroxyapatite (Ca10(PO4)6(OH)2
1 % present in body fluid
Blood calcium:
Blood Ca
Blood Ca level 9-11 mg/dl, No Ca in RBC
Plasma Ca is present in 2 forms:
1- Ionized (diffusible) 5-6 mg
It is the active form if ↓ leads to tetany
2- Non Ionized (bound) 4-5 mg, bound to albumin if ↓ no tetany
Factors affecting blood Ca (Ca hemostasis)
Hormonal factor
1- Parathyroid hormone (PTH)
↑ blood Ca by increasing
1- Absorption of Ca from intestine
2- Reabsorption of Ca from kidney
3- Resorbtion ( mobilization of Ca from bone to blood
4- ↑ P excretion
2- Calcitriol (1,25 dihydroxycholecalciferol) active vitamin D3, ↑ Ca by
increasing
1-Absorption of Ca from intestine
2-Reabsorption of Ca from kidney
3-Resorbtion (mobilization of Ca from bone to blood
Factors that decrease Ca level:
3- Calcitonin secreted from C cell of thyroid gland
↓ Ca in blood by deposition in bones
4- Estrogen
Has a role in Ca metabolism in bones as calcitonin ,
↓ Ca in blood by deposition in bones
In menopause , oestomalachia occurs due to ↓ estrogen
Other factors:
1- Solubility product : Optimum absorption of Ca occurs at a ratio of 2:1 or 1:1 with P.
2- pH : Ca is soluble and ionized at normal pH 7.4, alkalosis ↓ Ca
Functions of Ca (role of Ca in metabolism)
1-Enters in structure of bone and teeth
2-Contraction of muscle
3-Transmission of nerve impulse
4- ↓ neuromuscular irritability
so its deficiency leads to tetany that is treated by Ca
5- Blood and milk clotting:
Casein in milk + Ca in presence of rennin forms insoluble Ca paracasinate (milk clot) (give sense of fullness in infants).
6- Combines with calmodulin
which acts as second messenger for some hormone
7-Activates various enzymes (glycogen phosphorylase ,kinase).
Excretion
Mainly in feces, small amount in urine
Requirement
Adult 800 mg/day,
Pregnancy & lactation 800-1200 mg/day
Alterations in serum Ca
Hypercalcemia
Causes
1- Primary hyperparathyrodism due to adenoma in gland
2- Secondary hyperparathyrodism
3- ↑ intake of vitamin D
4- Cancer bones
5- Drugs
Effect hypercalcemia
Stone kidney, vomiting, abdominal cramp, constipation
Hypocalcemia
1-Hypoparathyrodism (primary or surgical removal)
2- Alkalosis
3- Kidney disease
Due to ↓ formation of calcitriol
Calcium Deficiency in bone
1-Rickets: in growing Children.
2- Osteomalacia in adults.
