In short: The female reproductive system consists of external organs, such as the labia, clitoris and hymen, and internal organs: the vagina (about 10 cm long), the uterus (7.5 × 5 cm), the two fallopian tubes (about 11 cm each) and the two ovaries, which produce oestrogen and progesterone. A girl is born with about two million eggs, and only one matures in each cycle.

It is formed from external and internal organs:

A-External female genital organs:

It is formed of organs around the vaginal opening:

Pubis:

It is the groin folds covered with hair, in mature adult woman it is horizontal in shape, it is not present in childhood, and it gets smaller after menopause. Hair growth at this area is one of the signs for puberty.

Labia majora.
Labia minora.

Clitoris:

It is equivalent to the penis in the male external genital organs; the visible part (glans) is small, but most of the clitoris lies under the skin, extending about 9–11 cm in total, and it is formed from tissues highly supplied with blood vessels that become engorged during sexual arousal.

Hymen:

It has different shapes, usually an incomplete membrane with an opening that allows menstrual blood to come out. It is elastic and may stretch or tear at first intercourse, but many women have no bleeding or visible tear, so the appearance of the hymen cannot reliably show whether intercourse has taken place.

Bartholin’s gland:

It lies at both sides of the vagina, and its function is to secret mucosal secretions that help in lubrication during intercourse.

Urethral orifice:

It lies just below clitoris.

Genital Area Hygiene

Video of Female Reproductive System

B-Internal Female Genital Organs:

Vagina:

It starts from the hymen till the cervix, it is lined with folded skin, and it’s around 10cm in length, but it is stretchable and becomes longer during labor and intercourse.

Uterus:

It’s like an inverted pear in shape, 7.5cm in length, 5cm in width, it starts from the cervix then uterine body and it’s lined by endometrium which is a special layer that lines the inside of the uterus, and gets thickened before each cycle in response to hormonal changes, then sheds out with cycle in the form of menstrual blood followed by formation of a new layer.

Fallopian tubes:

Extend from uterine body to the ovary with an average length of 11cm, and ends with a finger like processes, it is lined with certain type of cells that helps in transporting the oocyte from the ovary to the uterus, fallopian tubes are the sites where fertilization and the early stages of fetal development happen.

Cross Section of Female Pelvis

Video of Female Reproductive System

Ovary:

There are two ovaries at both sides of fallopian tubes they are formed from the external layer (cortex) that contain the follicles and inner layer (medulla) in between there are blood vessels and nerves, ovaries are equivalent to testis in the male, ovaries produce two hormones estrogen and progesterone .

Internal female genital organs

We will try to explain simply and as clear as we could what is the regular monthly cycle and what are the physiological changes that happen during each cycle, several hormones from different body organs control menstruation.

The most important of which are:

-At the base of the brain there is a gland called hypothalamus which secrets GNRH hormone.

-Just beneath the hypothalamus there is the pituitary gland that secrets two hormones FSH and LH, their secretion is under the effect of GNRH hormone.

-LH and FSH have a direct effect on the ovary to stimulate follicular growth and maturation, eventually ovulation at middle cycle and one oocyte is ready to be fertilized. The fertilized oocyte passes through fallopian tube to reach the endometrium, where the fetus grows, so if any blockage in one or both of fallopian tubes will affect pregnancy rate and any disturbance or decrease in the secretion of any previous hormone will affect fertilization.

Let’s explain it in details:

The hypothalamus starts secreting GNRH hormone in a pulsatile manner; this will induce the pituitary gland to secrete FSH and LH hormone, so its secretions differ during different stages of the cycle. During the first half of the cycle (before ovulation) GNRH is secreted every 1-1.5 hour, but after ovulation it is secreted much less frequent (every 4 hours).

Glandular Control of Menstrual Cycle

During the first half of the cycle there are low levels of estrogen, this will stimulate GNRH secretion which will stimulate the pituitary gland to secret FSH and LH hormones, these hormones induce the ovary to start follicular production, as the follicles grow, their surrounding cells start to secrete estrogen hormone so its level in blood will start to increase gradually during this time one of the follicles will be mature more than the other follicles and will grow faster and secret larger amounts of estrogen, rising level of estrogen causes a decrease in FSH and LH secretion, since the dominant follicle is capable of rapid growth, and fertilization it continues to grow even though FSH levels are falling, while the other follicles stop growing.

Rising level of estrogen helps in more maturation of the follicle, and in building up the endometrium. Estrogen level continues to increase until it causes a sudden increase in LH level, which is important in the final maturation of the follicle. 36 hours after this sudden increase ovulation happens during normal cycle, LH increase at day 12 of cycle and ovulation at day 14, after ovulation the oocyte is released, the follicle shrink to form the corpus luteum at outer layer of the ovary and it continue to secret estrogen and progesterone.

Menstrual cycle:

Both estrogen and progesterone decrease pituitary gland secretion of FSH and LH. If there is fertilization corpus luteum continue to secret estrogen and progesterone to prepare the endometrium to be ready for the fertilized ovum, from around the 7th–10th week of pregnancy the placenta gradually takes over the secretion of estrogen and progesterone, and the corpus luteum then regresses.

If there is no fertilization (or pregnancy), corpus luteum disappears and shrink gradually 10 days after ovulation which result in drop in the level of estrogen and progesterone, a few days later (about 14 days after ovulation) the endometrium sheds out in the form of menstrual bleeding, and the drop in hormonal level result in increase in GNRH, and initiation of new cycle.

It should be mentioned here that each follicle is formed from the oocyte surrounded by fluid, at the first half of cycle it is small in size, but at time of ovulation it reaches 16-26mm; this increase in size is due to increase in amount of fluid around the oocyte, (this increase in size can be followed using ultrasound), 36 hour before ovulation it grows faster, once LH level increase, ovulation happens. Regarding endometrial changes; at the first half of cycle (proliferative phase) when estrogen level is high, the endometrium increase in thickness and in blood supply, and then the endometrial glands start to secret mucosal substances that nourish the endometrium to be ready for the fertilized ovum this phase is called secretory phase if there is no pregnancy, the corpus luteum dissolves, estrogen and progesterone level decrease which leads to shedding of the endometrium and menstruation.

Ovulatory Cycle

Ovulatory and Endometrial changes during the Menstrual Cycle

Dear readers:

You may have some questions that cross your minds, we are glade to answer what we think is important for you?

How many oocytes does the woman have at birth?

At birth both ovaries contain around 2million oocyte; these remain dormant till puberty and most of them would have atresia, that is why at puberty their number decrease to 400.000 oocyte, the process of atresia continue, it is a lifelong process even during pregnancy, during each menstrual cycle about 20 follicle starts to grow, but only one follicle reaches maturation, and the rest of them disappear.

There are many factors that affect the rate of atresia, some are genetic and hereditary factors, but some are related to the environment like irradiation, medication, and smoking; that’s why the age of menopause (the age when menstruation stops) differs from one woman to another, that’s when all the oocytes go into atresia.

What is the follicle?

It is some sort of a sac filled with fluid that contains the oocyte inside.

How does ovulation happen? How could the oocyte come out of the follicle?

LH hormone is secreted from the pituitary gland; when the level of this hormone increase, it leads to formation of something like a hole in the membrane of the follicle, the oocyte comes out to be catch by the fimbrial end of the fallopian tube (finger like processes mentioned before).

Stages Of Oocyte Maturation

Video Stages Of Oocyte Maturation

Video Oocyte Formation

Does ovulation happen in alternating manner between each ovary?

Not exactly like that, ovulation whether from the right or left ovary is a random process, and you can never know which ovary will have the ovulation from till one or two days prior to ovulation and that can be done using ultrasound.

This question is so important for women with only one fallopian tube, most of the time the tube catches the oocyte from the ipsilateral ovary, but there are reported cases of pregnancy in women with one tube (on the left for example) and one ovary on the other side (on the right side) which is an indirect evidence that the fallopian tube can catch the oocyte from the contralateral ovary.

What is the regular menstrual cycle?

It is the cycle whose length is between 24 and 38 days, counted from the first day of one period to the first day of the next, with bleeding that lasts up to 8 days (most often 3–7 days) and a moderate amount of blood.

Does having a regular cycle means necessarily that ovulation happened?

Usually yes, but there are some exceptions in which the follicle grows incompletely, but still has the capability to secrete the hormones necessary for endometrial changes and menstruation.

Irregular cycles often mean that ovulation is not happening every month, but many women with irregular cycles still ovulate some of the time.

Dr Najeeb Layyous F.R.C.O.G

Consultant Obstetrician, Gynecologist and Infertility Specialist