Embed Notice

Aside from this, the phases of the estrus cycle are similar to the menstrual cycle. One or more ovarian follicles develop, and the endometrium begins to build up. The animal ovulates, releasing one or more eggs. At this point, either pregnancy occurs, or if it does not, hormonal changes signal that the endometrium isn't needed this cycle.

In animals with a menstrual cycle, at this point menstruation is triggered. In animals with an estrus cycle, the endometrium is reabsorbed.