![]() ![]() At this point in development, the primary function of amniotic fluid is the expansion of the amniotic sac, which allows room for the fetus to grow unimpeded. Gradually, the coelomic cavity shrinks as the amniotic cavity expands and completely disappears by week 12. This arrangement suggests that the coelomic fluid is essentially an extension of the placenta, providing the embryo with nutrients until the amniotic cavity becomes large enough to take over later in development. The exocoelomic cavity forms inside the extraembryonic mesoderm alongside the placental chorionic plate and is now believed to be an essential transfer interface and reservoir of nutrients for the embryo because coelomic fluid has shown to have ultrafiltrate of maternal serum as well as products derived from the placenta and secondary yolk sac. Before it disappears, the coelomic cavity acts as a transfer area as well as a reservoir of nutrients for the growing embryo. The coelomic fluid within the coelomic cavity stays in direct contact with the mesenchyme of the developing placenta villi during the first trimester. The formation of the coelomic cavity begins during the fourth week of gestation when the exocoelomic cavity splits the extraembryonic mesoderm into the splanchnic mesoderm lining and the somatic mesoderm. In early gestation, two fluid-filled sacs surround the embryo: the exocoelomic cavity and the amniotic cavity. During the embryonic period, amniotic fluid derives from both fetal and maternal factors such as water from maternal serum, coelomic fluid, and fluid from the amniotic cavity however, during late gestation, amniotic fluid is largely produced by fetal urine and lung secretions. ![]() The composition of amniotic fluid changes from early gestation to late gestation. Early gestation is the embryonic period which is from the start of fertilization to 8 weeks, and late gestation, which encompasses the fetal period 8 weeks to birth. ![]() The development of amniotic fluid organizes into early gestation and late gestation. ![]()
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