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10.4 - Female Reproductive Cycles

The female reproductive system is responsible for the production of the female gamete (ovum) and the production of sex hormones. The female reproductive tract also receives the male gamete during copulation (mating).

Endocrine control of the female reproductive system

There are two female reproductive cycles: the ovarian cycle and uterine cycle. The two cycles occur simultaneously but control different aspects of female reproduction. The ovarian cycle controls the maturation and release of an ovum, whereas the uterine cycle controls the preparation of the uterus for a potential fetus.

Ovarian cycle

Controlled by LH and FSH, which are released through the action of gonadotropin releasing hormone (GnRH)
FSH stimulates the growth of a follicle around the maturing ovum; a structure consisting of estrogen-producing cells that also nourish the ovum
LH stimulates ovluation; the release of a mature ovum from the ovary
Estrogen is produced by the follicle until ovulation
Progesterone is produced by the corpus luteum until blood LH levels drop

The ovarian cycle consists of two phases:

Follicular phase - The follicle grows, stimulated by FSH. Follicular cells release increasing amounts of estrogen until ovulation is stimulated by a surge in LH.
Luteal phase - The ruptured follicle is now known as the corpus luteum, which secretes progesterone.

Uterine cycle

Growth of the endometrium stimulated by estrogen (from follicular cells)
Growth and secretion of nutrients from the endometrium stimulated by progesterone (from the corpus luteum)

The uterine cycle consists of three phases:

Menstrual phase - Low estrogen and progesterone trigger the breakdown of the endometrial lining
Proliferative phase - Rising estrogen levels trigger the growth of the endometrial lining
Secretory phase - After ovulation, growth and secretion of the endometrial lining is stimulated by estrogen and progesterone from the corpus luteum

10.4 - Female hormone cycles

Figure 10.4.1 - Female reproductive cycles showing blood hormone concentrations. The ovarian cycle phases (follicular and luteal) control the uterine cycle phases (menstrual, proliferative and secretory) through hormones secreted by the follicle and corpus luteum.