Estrogen is a hormone secreted by the ovary. It is secreted in
greater amounts after menstruation and before ovulation. Among its
many effects, it causes up regulation of receptors in the uterus
for another hormone secreted by the ovary called progesterone.
Progesterone is secreted after ovulation. A major effect of
progesterone is to cause the uterus to become ready for the embryo
to attach to its wall following ovulation. Pregnancy cannot occur
unless the embryo attaches to the wall of the uterus. Predict the
consequences if the ovary secretes too little estrogen.