Calcium Metabolism and Hypocalcemia

Posted by e-Medical PPT Sunday, August 19, 2012
Calcium metabolism
99% of total body calcium in the bone .
1% in ICF ,ECF ,& cell membranes .
Calcium weight is 400mg/kg in infant & 950mg/kg in adult .

physiologic functions :
   1.blood coagulation .
      2.muscle contraction .
        3.neuromuscular transmission .
          4.Skeletal growth & mineralization
Ionized Ca is physiologically important .

Serum CA level is determined by net absorption (GI) & excretion (RENAL).
Each components is tightly regulated-hormonally- to keep normal serum level .
Total CA is usually measured & provides satisfactory assessment of ionized form .

Calcium regulation :mainly by 3 common hormones :
    1}Parathyroid hormone
          2}Vitamin D
              3}Calcitonin
Vitamin D
Actions:
1)increase Ca absorption from intestine.
2) increase PO4 absorption from intestine.
3) increase renal reabsorption of Ca &PO4.
4) increase bone resorption from old bone &mineralize new bone{net resorption} .
Overall effect :increase serum Calcium and Phosphate .

PTH hormone
Major hormone in regulation serum Ca .]
Synthesis & secreted from chief cells of parathyroid gland .
Actions :
1)increase bone resorption..increase serum Calcium and Phosphate .
2)increase renal Calcium reabsorption .
3)increase Calcium absorption from intestine indirectly by increase VITD .
4)decrease Phosphate reabsorption from proximal tubules …increase ionized Calcium .
Overall effect :increase serum Calcium & decrease serum Phosphate.

Hypocalcemia
Causes of hypocalcemia
Specific causes in neonates
Early neonatal hypocalcemia:(within 48-72 hour of birth)
Causes:    1- prematurity: poor intake, decrease response to Vit. D, increase calcitoni, decrease albumin.
    2- birth asphyxia: delayed introduction to feed, increase calcitonin, increased endogenous PO4 load, alkali therapy.
    3- infant of diabetic mother: functional parahypothyroidism induced by Mg defficiency has predominant role
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