Final answer:
After ovulation, the endometrium thickens due to the increased secretion of progesterone and estrogen by the corpus luteum, preparing for the possible implantation of a fertilized egg.
Step-by-step explanation:
Immediately following ovulation, the endometrium begins to thicken in preparation for the potential implantation of a fertilized egg. This thickening is critical for a potential pregnancy as it creates a nourishing environment for an embryo to grow. The hormones progesterone and estrogen play a significant role in this process. The corpus luteum, which is what remains of the follicle after ovulation, starts to secrete more progesterone, which maintains the endometrium. If the egg is fertilized, it will travel through the fallopian tube and reach the uterus, where it may implant into the thickened endometrial lining, leading to pregnancy.