الفهرس 
premature &low birth weight infantsOnly 14 pages are availabe for public view
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Abstract
The major physiologic control of bone mineralization in
infancy involves calciwn and phosphorus. Calcitropic hormones
(parathyroid honnone, calcitonin and
1, 25 dihydroxyvitamin D)
modulate the response
of major end organs - intestine, kidney and
bone
- to balance the need to maintain a relatively stable
extracellular biochemical environment with the need for adequate
mineralization
of the bone. Clinical bone demineralization occurs
primarily
in extremely premature infants (Koo a11d Tsa11g, 1984).
Parathyroid honnone is a polypeptide secreted by the
parathyroid glands to defend against hypocalcemia by controlling
the level
of ionized calcium in extracellular fluid through its direct
actions on mineral transport
in bone and kidney and its secondary
actions on mineral transport
in intestine (mediated by l, 25 (OH),
D) and it serves as a principal regulator of process of
mineralization rather than calcitonin (Aurbach et aL, 1992).
The principal matemal adjustrnent of calcium homeostasis
during pregnancy is through an increase in parathyroid honnone
secretion which maintains the serum cakium concentrations in
the face of placental calcium transfer. The placenta transports
calcium ions actively, making the fetus hypercalcemic relative to
its mother, which in tum stimulates calcitonin release and perhaps
suppresses parathyroid hormone secretion
by the fetus (Pitkill,
1985).