Morula
Also known as: compaction
A solid ball of ≈12–32 blastomeres ("mulberry") formed ≈3–4 days after fertilisation, in which compaction separates inner from outer cells; it enters the uterine cavity at about day 4.
Overview
At about the 8-cell stage the blastomeres flatten against each other and become tightly linked by E-cadherin and tight junctions — compaction. This creates, for the first time, cells with different positions: outer cells, which become polarised and form the trophoblast, and inner cells, which form the inner cell mass. By ≈day 3–4 the embryo is a morula of about 16 cells, still enclosed by the zona pellucida, and it passes through the uterotubal junction into the uterine cavity.
- Location
Distal uterine tube, entering the uterine cavity at ≈day 4.
Function
- First segregation of embryonic (inner) and trophoblast (outer) lineages.
Clinical significance
Tubal transport
If tubal transport is delayed (cilia damaged by infection or smoking, scarring), the embryo may develop to the implantation stage while still in the tube — ectopic pregnancy.
Compiled from standard anatomy and physiology references — see the Reproductive System sources. For education only; not medical advice.