ECR L31
THE OVARY & THE FEMALE REPRODUCTIVE TRACT I
27/01/2000
Dr S MILLIGAN

One double sided handout was given which covers this lecture and the next (ECR L32)

Females are different to males because there are ovarian cycles after puberty and until menopause, rather than a constant production, like there is in males.

In a normal, non-lactating, non-contraceptive pill taking, etc. female:

Ovaries produce eggs and hormones (oestradiol - E2 and progesterone). The hormones feedback onto the reproductive tract, mammaries, cardiovascular system, liver, bone etc. - they feedback to the pituitary and hypothalamus, and this all occurs in a cyclical nature.

MENSTRUAL CYCLE

Reflects the shedding of the uterine lining. It is an external reflection of what the ovaries are doing.

a) Variations in cycle length are normal (24 to 32 days is OK)
b) Variations can be due to:

variations in follicular phase
anovulatory cycles
variations in luteal phase

c) Changes with age are normal

Ovulation is a critical event. Fertility can’t be determined just by knowing when menstruation occurs. Events just before and after ovulation are important (days pre- and post-ovulation).

CRITICAL STEPS IN THE OVARIAN CYCLE

Follicular growth (follicles)
Ovulation (egg)
Maintenance of the corpus luteum (major endocrine role is to secrete progesterone and a small amount of oestradiol)
Either: luteal regression (with menstruation); or pregnancy (with continued luteal maintenance - no menstruation)

CONTROL OF OVARIAN FUNCTION

The follicle is 1.5 to 2cm in diameter, and can be viewed with ultrasound. In the follicular phase, the dominant follicle, along with its contained oocyte develop. Why is there normally just one oocyte in humans? See later for explanation, but control is required to prevent this. Hormones are produced: what hormones? From where? How are they controlled? What are the effects?

The oocyte in the follicle is still haploid - it hasn’t completed meiosis (stuck at the first meiotic division) and dormant. The follicle is supplying the oocyte through the zona pellucida. Around the oocyte and zona pellucida is the "cumulus" and fluid.

The main follicle output is oestradiol (E2) from granulosa cells. To get it out of the follicle, it is driven by LH and FSH, which need to be in a correct balance. LH stimulates thecal cells to make androgens, therefore androgens are a natural part of the female ovarian production.

In polycystic ovarian syndrome there is a too high production of androgens, caused by LH/FSH imbalance, and causes excess hair growth.

FSH takes androgens and supplies them as precursors to oestradiol.

1) When do follicles start growing? 60 days previous to the start of the menstrual cycle. Early growth control isn’t really known.
2) How many follicles are growing? 30 to 50 follicles, only one getting to the mature state (dominant follicle).

Reducing the driving force all the time. Not all the follicles are the same. The least advanced follicles require the most FSH:

Therefore FSH is the limiting factor. To induce multiple ovulations, give the patient FSH-like drugs.

NB: as the follicle grows, E2 is produced which feeds back (negatively) on to the hypothalamic-pituitary axis. E2 is involved in uterine growth, fallopian tubes, cervix, vagina.