QS Study

Fetoplacental Unit is the interaction between the placenta and the fetal adrenal cortex in the production of steroids. It is a functional compartment responsible for synthesizing hormones that maintain pregnancy. The androgen dehydroepiandrosterone (DHEA) is an important steroid produced by the adrenal gland during fetal development. The fetus, placenta, and mother are interdependent and constitute a functional unit called the fetoplacental unit.

Fig: Fetoplacental Unit Mechanism


(a) The placenta synthesizes pregnenolone and progesterone from cholesterol. Placental progesterone also diffuses into the fetus where it is converted to corticosteroids.

(b) Some progesterone enters the fetal circulation and provides the substrate for the formation of cortisol and corticosteroid in the fetal adrenal gland. DHEA synthesis in the spiny mouse brain changes from predominantly neuronal in fetal life to white matter in the adult brain.

(c) Some of the pregnenolone enters the fetus with the pregnenolone synthesized in the fetal liver for the formation of dehydroepiandrosterone sulfate (DHEAS) and 16-hydroxy dehydroepiandrosterone sulfate (16- OHDHEAS) in the fetal adrenal.

(d) DHEAS and 16-OH-DHEAS are transported back to the placenta, where DHEAS forms estradiol and 16-OH DHEAS form estriol. The principle of estrogen formed is estriol.

(e) Estriol, the major circulating hormone in pregnancy is synthesized from DHEAS. The conversion requires mainly two enzymes: 16a hydroxylase and aromatase.

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