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Aspects of Praematurity and Dysmaturity - Groningen 10-12 May 1967 (Paperback, Softcover reprint of the original 1st ed. 1968)
Loot Price: R1,562
Discovery Miles 15 620
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Aspects of Praematurity and Dysmaturity - Groningen 10-12 May 1967 (Paperback, Softcover reprint of the original 1st ed. 1968)
Series: Nutricia Symposia, 2
Expected to ship within 10 - 15 working days
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The concept of the foeto-placental unit as an integrated endocrine
organ has been defined recently by many in vivo studies at the
17th- 20th week of gestation. A functioning foeto-placental unit is
necessary for most of the increased oestrogen production of
pregnancy and for the provision of glucocorticoids and aldosterone
to the foetus. Neither the foetus nor the placenta alone have the
necessary enzyme systems for the synthesis of these groups of
steroids. However, when the foetus and placenta function as a unit,
all of the enzyme systems are present for the synthesis of these
steroids from circulating cholesterol. The placenta, but not the
mid-gestation foetal adrenal, can synthesize physiologically
significant amounts of pregnenolone from circulating cholesterol.
Part of the pregnenolone is converted to progesterone in the
placenta by the 3 -HSD system (absent in the foetus). The
progesterone is transferred to the foetus where it is transformed
by C-II, C-17, C-18 and C-21 hydroxylases (all absent in the
placenta) to cortisol, corticosterone and aldosterone. Pregnenolone
transferred from the placenta to the foetus undergoes
171X-hydroxylation, side chain splitting and sulfurylation (absent
in the placenta) and is converted to DHAS. The DHAS may undergo
161X-hydroxylation (absent in the placenta) in the foetal liver and
be transported to the placenta as 161X-OH-DHAS. There it is
subjected to a neutral steroid sulfatase (absent in the foetus) and
is converted to oestriol by action of the 3 -HSD system and the
aromatizing enzyme system."
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