Corpus luteum

In the cycle of egg maturation, ovulation is the step at which the ovum is released into the fallopian tube. 

Up to this point, the premature egg is encapsulated in the follicle which remains behind during ovulation which becomes the corpus luteum.

If the egg is fertilised, the corpus luteum will trigger increased production of the hormones progesterone and estrogen for about 10 weeks.

If the egg is not fertilised, the corpus luteum will only increase the production of these hormones for 2 weeks.