Amniotic sac

This article is about two of the layers of the fetal membranes and their contents. For the other layers, see Fetal membranes.

Amniotic sac
Anatomical terminology

The amniotic sac, also called the bag of waters[1][2] or the membranes,[3] is the sac in which the embryo and later fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo (and later fetus) until shortly before birth. The inner of these membranes, the amnion, encloses the amniotic cavity, containing the amniotic fluid and the embryo. The outer membrane, the chorion, contains the amnion and is part of the placenta. On the outer side, the amniotic sac is connected to the yolk sac, the allantois, and via the umbilical cord, the placenta.[4]

The yolk sac, amnion, chorion, and allantois are the four extraembryonic membranes that lie outside of the embryo and are involved in providing nutrients and protection to the developing embryo.[5] They form from the inner cell mass; the first to form is the yolk sac followed by the amnion which grows over the developing embryo. The amnion remains an important extraembryonic membrane throughout prenatal development. The third membrane is the allantois, and the fourth is the chorion which surrounds the embryo after about a month and eventually fuses with the amnion.[6]

Amniocentesis is a medical procedure where fluid from the sac is sampled during fetal development, between 15 and 20 weeks of pregnancy, to be used in prenatal diagnosis of chromosomal abnormalities and fetal infections.[7]

  1. ^ Freshwater, Dawn; Masiln-Prothero, Sian (22 May 2013). Blackwell's Nursing Dictionary. John Wiley & Sons. ISBN 978-1-118-69087-1. Retrieved 11 March 2016.
  2. ^ "Definition of BAG OF WATERS". www.merriam-webster.com. Retrieved 6 October 2021.
  3. ^ "Premature rupture of membranes: MedlinePlus Medical Encyclopedia". medlineplus.gov. Retrieved 6 October 2021.
  4. ^ Larsen, WJ (2001). Human Embryology (3rd ed.). Churchill Livingstone. p. 40. ISBN 0-443-06583-7.
  5. ^ Wolpert (2015). Principles of development (Fifth ed.). Oxford, United Kingdom. p. 666. ISBN 978-0-19-967814-3.{{cite book}}: CS1 maint: location missing publisher (link)
  6. ^ Carlson, Bruce M. (2014). "Placenta and Extraembryonic Membranes". Human Embryology and Developmental Biology. pp. 117–135. doi:10.1016/B978-1-4557-2794-0.00007-3. ISBN 978-1-4557-2794-0.
  7. ^ "Amniocentesis". nhs.uk. 20 October 2017. Retrieved 6 October 2021.