User:Anacambursano/sandbox

Function
The fetal membrane surrounds the fetus during the gestational period and ensures maintenance of pregnancy to delivery, protection of the fetus as well as being critical in maintaining the conditions necessary for fetal health.

Barrier function
The fetal membranes separate maternal tissue from fetal tissue at a basic mechanical level. The fetal membrane is composed of a thick cellular chorion covering a thin amnion comprised of dense collagen fibrils. The amnion is in contact with the amniotic fluid and ensures structural integrity of the sac due to it's mechanical strength. The underlying chorion is fused to the decidua at the maternal-fetal interface. This interaction is vital in controlling the local immune systems which in turn is vital for maintaining a semi-allogeneic fetus. At the end of gestation, a 'weak zone' develops in the foetal membrane overlying the cervix due to collage remodelling. This eventually leads to rupture of the fetal membrane and the onset of labour.

Signalling of fetal maturation and parturition
As pregnancy advances to term, the fetal membranes undergo weakening. The amnion is vital in the synthesis of prostaglandins which reach the myometrium and create and initiate parturition. The chorion expresses chemicals that balance synthesis and metabolism of these prostaglandins to ensure that the myometrium is not activated pre-term. Prostaglandin E2 is thought to be synthesized by cells in the amnion and is essential in dilation of the cervix at the initiation of parturition. Glucocorticoids have been implicated in fetal maturation, regulation of immune response and many other pregnancy associated changes. As well as it's function in parturition, Prostaglandin E2 is vital for fetal lung maturation. Additionally, there is an abundance of 11β-hydroxysteroid dehydrogenase 1 expressed in the foetal membranes. This enzyme converts biologically inactive cortisone into active cortisol, another chemical vital for fetal maturation and labour initiation.