Female reproductive cycle - T3 W5

The ovarian cycle

•A series of events that take place within the ovaries.

•Involves the maturation of an egg and its release into a Fallopian tube.

•Length of cycle is highly variable – usually ranges from 20 to 40 days, with an average cycle length of 28 days.

Ovarian cycles stages

•Follicles at different stages of maturation are distinguishes by their size and by their structure:

⚬Primary follicles – have a single layer of epithelial cells surrounding a primary oocyte

⚬Secondary follicles – have multiple layers of epithelial cells surrounding a secondary oocyte.

⚬Mature follicles (previously called a Graafian follicle) have a fluid-filled cavity. Just before ovulation, the secondary oocyte inside the follicle resumes meiosis and stops at metaphase II.

Ovarian cycle phases - Follicular phase

⚬If the cycle is 28 days on average, the follicular phase occurs over the first 14 days of the ovarian cycle.

⚬This phase involves the maturation of the ovarian follicle; from the primary follicle, to the secondary follicle, to the mature follicle.

⚬The follicular phase ends with ovulation on day 14 of the ovarian cycle.

Ovarian cycle phases - Ovulation

⚬Occurs on day 14.

⚬Ovulation occurs when the ballooning ovary wall ruptures and expels the secondary oocyte into the peritoneal cavity.

⚬This secondary oocyte is then swept up into the Fallopian tube by the fimbriae.

Ovarian stages phases - Luteal phase

⚬Days 14-28.

⚬After ovulation, the ruptured follicle collapses.

⚬The remaining cells enlarge and form a new structure called the corpus luteum (‘yellow body’).

⚬The corpus luteum is an endocrine gland and produces and releases two hormones (more on this later!).

⚬If pregnancy does not occur, the corpus luteum starts degenerating after about 10 days and its hormonal output ends.

⚬All that ultimately remains is a scar called the corpus albicans (‘white body’).

Ovarian cycle phases - diagram

Menstrual cycle

•While the ovarian cycle is occurring, the uterus is also going through a series of changes called the menstrual cycle.

•The changes in the uterine lining, the endometrium, are in preparation for a developing embryo in case the egg released at ovulation is fertilised.

•The average length of the menstrual cycle is also 28 days.

Menstrual cycle phases - menstruation

⚬Shedding of the uterine lining.

⚬The thick, functional layer of the endometrium detaches from the uterine wall, a process accompanied by bleeding.

⚬The detached tissue and blood pass out through the vagina as the menstrual flow.

⚬On average 5 days.

Menstrual cycle phases - Proliferative Phase

⚬The endometrium rebuilds itself.

⚬New layer grows and thickens, its glands enlarge, and its spiral arteries increase in number.

⚬Becomes velvety, thick and vascularised.

⚬From the end of menstruation until approximately day 14.

Menstrual cycle phases - Secretory Phase

⚬The endometrium prepares for an embryo to implant.

⚬Endometrial glands enlarge, coil and begin secreting nutrients into the uterine cavity.

⚬These nutrients will sustain the embryo until it has implanted in the blood-rich endometrial lining.

⚬Days 14-28.

Ovarian + menstrual cycle diagram

Menarche

Onset of menstruation

menopause

Cessation of menstruation