Why is this process of moving molecules in and out of cells through a protein channel called "facilitated" diffusion?

Because it uses a carrier at the cell membrane

Explanation:

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

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