Corpus luteum follicle-stimulating hormone (FSH). A new corpus luteum develops with each menstrual cycle. The "corpus luteum" develops from an ovarian follicle during the luteal phase of the menstrual cycle or oestrous cycle, following the release of a secondary oocyte from the follicle during ovulation. The follicle first forms a corpus hemorrhagicum before it becomes a corpus luteum, but the term refers to the visible collection of blood, left after rupture of the follicle, that secretes progesterone. While the oocyte (later the zygote if fertilization occurs) traverses the Fallopian tube into the uterus, the corpus luteum remains in the ovary. The corpus
Estrous cycle that releases sex hormones including estrogens and progesterone. However, species vary significantly in the detailed functioning. One difference is that animals that have estrous cycles resorb the endometrium if conception does not occur during that cycle. Animals that have menstrual cycles shed the endometrium through menstruation instead. Another difference is sexual activity. In species with estrous cycles, females are generally only sexually active during the estrus (oestrus) phase of their cycle . This is also referred to as being "in heat". In contrast, females of species with menstrual cycles can be sexually active at any time in their cycle, even