Amniotic sac - wikipedia Amniotic sac Amniotic sac 10 - week - old human fetus surrounded by amniotic fluid within the amniotic sac The amniotic sac opened during afterbirth examination. Dorlands / Elsevier s_01 / 12716695 Anatomical terminology ( edit on Wikidata ) The amniotic sac, commonly called the bag of waters, sometimes the membranes, is the sac in which the 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 fetal membranes, the amnion, encloses the amniotic cavity, containing the amniotic fluid and the fetus. 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, to the placenta. Amniocentesis is a medical procedure where fluid from the sac is sampled to be used in prenatal diagnosis of chromosomal abnormalities and fetal infections. Contents 1 Structure 1.1 Development 1.2 Birth 2 Function 3 Clinical significance 4 References 5 External links Structure Amniotic cavity in human embryo 1.3 mm. long The amniotic cavity is the closed sac between the embryo and the amnion, containing the amniotic fluid. The amniotic cavity is formed by the fusion of the parts of the amniotic fold, which first makes its appearance at the cephalic extremity, and subsequently at the caudal end and sides of the embryo. As the amniotic fold rises and fuses over the dorsal aspect of the embryo, the amniotic cavity is formed. Development At the beginning of the second week, a cavity appears within the inner cell mass and when it enlarges it becomes the amniotic cavity. The floor of the amniotic cavity is formed by the epiblast. Epiblast migrates between the epiblastic disc and trophoblast. In this way the epiblastic cells migrate between the embryoblast and trophoblast. The floor is formed by the epiblast which later on transforms to ectoderm while the remaining cells which are present between the embryoblast and trophoblast are called amnioblasts ( flattened cells ). These cells are also derived from epiblast which is transformed into ectoderm. The amniotic cavity is surrounded by a membrane, called the amnion. As the implantation of the blastocyst progresses, a small space appears in the embryoblast, which is the primordium of the amniotic cavity. Soon amniogenic ( amnion forming cells ) amnioblasts separate from the epiblast and line the amnion, which encloses the amniotic cavity. The epiblast forms the floor of the amniotic cavity and is continuous peripherally with the amnion. The hypoblast forms the roof of the exocoelomic cavity and is continuous with the thin exocoelomic membrane. This membrane along with hypoblast forms the primary yolk sac. The embryonic disc now lies between the amniotic cavity and the primary yolk sac. Cells from the yolk sac endoderm form a layer of connective tissue, the extraembryonic mesoderm, which surrounds the amnion and yolk sac. Birth If, after birth, the complete amniotic sac or big parts of the membrane remain coating the newborn, this is called a caul. When seen in the light, the amniotic sac is shiny and very smooth, but tough. Once the baby is pushed out of the mother 's uterus, the umbilical cord, placenta, and amniotic sac are pushed out in the after birth. Function The amniotic sac and its filling provide a liquid that surrounds and cushions the fetus. It allows the fetus to move freely within the walls of the uterus. Buoyancy is also provided. Clinical significance Chorioamnionitis is inflammation of the amniotic sac ( chorio - + amnion + - itis ), usually because of infection. It is a risk factor for neonatal sepsis. During labor, the amniotic sac must break so that the child can be born. This is known as rupture of membranes ( ROM ). Normally, it occurs spontaneously at full term either during or at the beginning of labor. A premature rupture of membranes ( PROM ) is a rupture of the amnion that occurs prior to the onset of labor. An artificial rupture of membranes ( AROM ), also known as an amniotomy, may be clinically performed using an amnihook or amnicot in order to induce or to accelerate labour. References Jump up ^ `` Blackwell 's Nursing Dictionary ''. Retrieved 11 March 2016. Jump up ^ What is the amniotic sac ?, NHS Jump up ^ Larsen, WJ ( 2001 ). Human Embryology ( 3rd ed. ). Churchill Livingstone. p. 40. ISBN 0 - 443 - 06583 - 7. Jump up ^ The word amniocentesis itself indicates precisely the procedure in question, Gr. ἀμνίον amníon being the `` inner membrane round the foetus '' and κέντησις kéntēsis meaning `` pricking '', i.e. its puncture in order to retrieve some amniotic fluid. Jump up ^ `` Diagnostic Tests -- Amniocentesis ''. Harvard Medical School. Archived from the original on 2008 - 05 - 16. Retrieved 2008 - 07 - 15. External links https://www.mun.ca/biology/scarr/Amniotic_egg.html http://staff.um.edu.mt/acus1/IMPLANTATION.htm Membranes of the fetus and embryo Embryo Trophoblast Cytotrophoblast Syncytiotrophoblast Intermediate trophoblast Allantois Decidua Decidual cells Chorionic villi / Intervillous space Amnion sac cavity Fetus Umbilical cord Umbilical artery Umbilical vein Wharton 's jelly Circulatory Placenta Chorion Other Blastocoel Heuser 's membrane Vitelline duct Gestational sac Pregnancy and childbirth Planning Birth control Natural family planning Pre-conception counseling Conception Assisted reproductive technology Artificial insemination Fertility medication In vitro fertilisation Fertility awareness Unintended pregnancy Testing 3D ultrasound Obstetric ultrasonography Pregnancy test Home testing Prenatal diagnosis Prenatal Anatomy Amniotic fluid Amniotic sac Endometrium Placenta Development Fundal height Gestational age Human embryogenesis Maternal physiological changes Postpartum physiological changes Care Nutrition Environmental toxicants In pregnancy Prenatal Concomitant conditions Drinking Diabetes mellitus Smoking Vaping SLE Sexual activity during pregnancy Procedures Amniocentesis Cardiotocography Chorionic villus sampling Nonstress test Abortion Childbirth Preparation Adaptation to extrauterine life Bradley method Hypnobirthing Lamaze Nesting instinct Roles Doula Men 's roles Midwife Obstetrician Perinatal nurse Delivery Bloody show Childbirth positions Home birth Multiple birth Natural childbirth Pelvimetry / Bishop score Cervical dilation Cervical effacement Position Presentation Breech Cephalic Shoulder Rupture of membranes Unassisted childbirth Uterine contraction Water birth Postpartum Child care Congenital disorders Sex after pregnancy Obstetric history Gravidity Parity TPAL Retrieved from `` https://en.wikipedia.org/w/index.php?title=Amniotic_sac&oldid=796962079 '' Categories : Body fluids Developmental biology Embryology Obstetrics Human anatomy Midwifery Hidden categories : Medicine infobox template using Dorlands parameter Use dmy dates from April 2017 Talk Contents About Wikipedia Català Dansk Deutsch Ελληνικά Español Français Հայերեն Ido Italiano עברית Norsk Polski Português Simple English کوردی Svenska தமிழ் 中文 Edit links This page was last edited on 24 August 2017, at 03 : 43. 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Question: what is the function of the amniotic sac
Answer: the sac in which the fetus develops in amniotes