Editing Blastocoel (section)

== In mammals==
After fertilization, the [[zygote]] undergoes several rounds of [[Cleavage (embryo)|cleavage]] divisions forming daughter cells known as [[blastomere]]s. At the 8- or 16-cell stage, the embryo undergoes [[Cleavage (embryo)#Compaction|compaction]] and forms the [[morula]]. Eventually, the [[morula]] is a solid ball of cells that has a small group of internal cells surrounded by a larger group of external cells. Then blastomeres undergo [[cellular differentiation]] with internal cells adopting the [[inner cell mass]] fate and the external layer becoming [[trophectoderm]]. The inner cell mass will go on to become the actual embryo. The external, surrounding cells develop into [[trophoblast]] cells, which only contribute to extra-embryonic tissues. At this stage there is no [[lumen (anatomy)|lumen]] within the embryo. In a process called [[Cavitation (embryology)|cavitation]], [[trophectoderm]] cells transport fluid into the embryo to create a blastocoel, the fluid-filled [[lumen (anatomy)|lumen]]. The membranes of the [[trophectoderm]] cells contain sodium (Na<sup>+</sup>) pumps, Na<sup>+</sup>/K<sup>+</sup>- ATPase and Na<sup>+</sup>/H<sup>+</sup> exchangers, that pump sodium into the embryo. The oviduct cells stimulate these trophoblast sodium pumps as the fertilized egg travels down the fallopian tube towards the uterus.<ref name="Wiley">{{cite journal |last1=Wiley |first1=Lynn M. |title=Cavitation in the mouse preimplantation embryo: and the origin of nascent blastocoele fluid |journal=Developmental Biology |volume=105 |issue=2 |pages=330–42 |year=1984 |pmid=6090240 |doi=10.1016/0012-1606(84)90290-2 }}</ref> The accumulation of sodium pulls in water through [[osmosis]].<ref name="CIBA"/> The accumulation of water breaks open cell-cell contacts via [[hydraulic fracturing]].<ref name="science.org">{{cite journal | url=https://www.science.org/doi/full/10.1126/science.aaw7709 | doi=10.1126/science.aaw7709 | title=Hydraulic fracturing and active coarsening position the lumen of the mouse blastocyst | date=2019 | last1=Dumortier | first1=Julien G. | last2=Le Verge-Serandour | first2=Mathieu | last3=Tortorelli | first3=Anna Francesca | last4=Mielke | first4=Annette | last5=De Plater | first5=Ludmilla | last6=Turlier | first6=Hervé | last7=Maître | first7=Jean-Léon | journal=Science | volume=365 | issue=6452 | pages=465–468 }}</ref> To form a single lumen, the fluid from multiple water pockets collects into a single entity in process akin to [[Ostwald ripening]].<ref name="science.org"/> The blastocoel further expands and the inner cell mass becomes positioned on one side of the trophoblast cells forming a mammalian blastula, called a [[blastocyst]]. The axis formed by the [[inner cell mass]] and the blastocoel is the first axis of symmetry of mammalian embryo and determines its attachment point to the uterus.