Practice question

Blastocyst stage is defined by formation of fluid-filled blastocoel cavity segregating embryonic lineages. After compaction outer cells polarize, establish E-cadherin-mediated adherens junctions and tight junctions sealing intercellular spaces. Basolaterally positioned Na/K ATPase pumps sodium into intercellular clefts, water follows osmotically via aquaporins causing intercellular spaces to coalesce into single cavity. Expansion of blastocoel positions inner cell mass at embryonic pole and trophectoderm surrounding cavity. Cavity formation marks preparation for hatching, implantation competency, lineage differentiation essential for survival, nutrient exchange and epithelial transport functions.