Fetal membranes

Fetal membranes are structures that form around an embryo or fetus during pregnancy in mammals, including humans. They are composed of the amnion, the chorion, the yolk sac, and the allantois. These membranes play crucial roles in the protection, nourishment, and development of the fetus.

Structure

The fetal membranes are composed of four main components:

• Amnion: This is the innermost layer of the fetal membranes. It forms a protective sac around the fetus and is filled with amniotic fluid, which cushions the fetus and maintains a constant temperature in the womb.

• Chorion: This is the outermost layer of the fetal membranes. It contributes to the formation of the placenta, which provides oxygen and nutrients to the fetus.

• Yolk sac: In humans, the yolk sac is responsible for the initial circulation and is a source of primordial germ cells. It also contributes to the development of the umbilical cord.

• Allantois: This structure is involved in early fluid exchange between the embryo and the yolk sac.

Function

The primary function of the fetal membranes is to protect and nourish the fetus. The amnion and chorion create a barrier against physical impact, bacterial infection, and maternal immune cells. The chorion and its villi also facilitate the exchange of nutrients and waste products between the mother and fetus.

The yolk sac provides nutrition to the early embryo before the placenta is fully formed. The allantois aids in gas and waste exchange.

Clinical significance

Damage or disease in the fetal membranes can lead to complications in pregnancy, such as preterm birth, intrauterine growth restriction, and preeclampsia. In some cases, the membranes may rupture prematurely, a condition known as premature rupture of membranes (PROM).

See also

• Placenta
• Amniotic fluid
• Umbilical cord