The female reproductive system
The female system produces eggs, supports a developing pregnancy, and cycles roughly monthly under hormonal control.
Anatomy
The ovaries, beside the uterus, produce eggs (oocytes) and the hormones oestrogen and progesterone. Uterine (fallopian) tubes carry eggs toward the uterus and are the usual site of fertilisation. The uterus has a muscular wall (myometrium) and a lining (endometrium) that thickens each cycle. The cervix opens into the vagina, the birth canal.
Oogenesis
Unlike sperm production, egg production starts before birth: a female is born with about 1-2 million immature eggs, arrested partway through meiosis. Only about 400-500 will be ovulated in a lifetime. Meiosis completes only if the egg is fertilised, and divides cytoplasm unequally, producing one large egg and small polar bodies.
The ovarian cycle
Each month, FSH stimulates several follicles to develop, usually one becoming dominant. A surge of LH around day 14 of a typical 28-day cycle triggers ovulation, releasing the egg. The empty follicle becomes the corpus luteum, which secretes progesterone and oestrogen. If no pregnancy occurs, it degenerates after about 10-14 days.
The uterine (menstrual) cycle
The endometrium cycles alongside the ovary. During menstruation (days 1-5), the lining is shed. In the proliferative phase, rising oestrogen rebuilds it. After ovulation, in the secretory phase, progesterone makes it rich in blood vessels and glands, ready for an embryo. When progesterone falls, the lining is shed again.
Hormonal feedback
Moderate oestrogen normally inhibits LH and FSH (negative feedback), but high, sustained oestrogen just before ovulation flips to positive feedback, causing the LH surge. Hormonal contraceptives work mainly by providing steady oestrogen and/or progestin that prevent this surge, stopping ovulation.
Mammary glands
Breasts contain mammary glands that produce milk after childbirth. Prolactin stimulates milk production, and oxytocin, released when a baby suckles, triggers milk ejection. Breast cancer is the most commonly diagnosed cancer in women worldwide; screening helps find it early.
Menopause
Menopause, usually between ages 45 and 55, occurs when the ovaries run out of responsive follicles and stop cycling; it is confirmed after 12 months without periods. Falling oestrogen can cause hot flushes and sleep problems and speeds bone loss, raising osteoporosis risk.
Female health topics
Endometriosis occurs when endometrial-like tissue grows outside the uterus, causing pain. Polycystic ovary syndrome (PCOS) involves hormonal imbalance and irregular ovulation, a common cause of reduced fertility. Cervical cancer is mostly caused by human papillomavirus (HPV), which vaccination and screening greatly reduce.
Key takeaways
Ovaries make eggs and hormones; fertilisation usually occurs in the uterine tubes; the endometrium prepares for implantation. Females are born with all their immature eggs. FSH develops follicles; an LH surge triggers ovulation; the corpus luteum makes progesterone. The uterine cycle has menstrual, proliferative, and secretory phases. Oestrogen switches to positive feedback before ovulation. Menopause ends cycling.
Flashcard
Makes eggs, oestrogen, progesterone
Check your understanding
What triggers ovulation?