Blastocyst formation involves flux of:
Blastocyst cavitation requires transepithelial fluid transport generating blastocoel. Outer trophectoderm cells differentiate into polarized epithelium sealed by tight junctions expressing Na/K ATPase pumps on basolateral membranes. Active pumping of sodium ions into nascent intercellular spaces creates electrochemical and osmotic gradient driving water influx via aquaporins 3 and 9, inflating cavity. Potassium is pumped oppositely, calcium important for adhesion not flux, chloride follows passively. Inhibition of Na/K pump with ouabain prevents blastocoel expansion, embryo remains morula. Hen
Ref: Watson & Barcroft, Philos Trans 2001: Sodium pump role in blastocoel formation and trophectoderm transepithelial transport.
