The female reproductive system is designed to carry out several functions. It produces the female egg cells necessary for reproduction, called the ova or oocytes. The system is designed to transport the ova to the site of fertilization.
Conception, the fertilization of an egg by a sperm, normally occurs in the Fallopian tubes. The next step for the fertilized egg is to implant into the walls of the uterus, beginning the initial stages of pregnancy.
If fertilization and/or implantation does not take place, the system is designed to menstruate (the monthly shedding of the uterine lining). In addition, the female reproductive system produces female sex hormones that maintain the reproductive cycle.
The main external structures of the female reproductive system include:
The labia majora enclose and protect the other external reproductive organs. The labia majora contain sweat and oil-secreting glands. After puberty, the labia majora are covered with hair.
They lie just inside the labia majora, and surround the openings to the vagina (the canal that joins the lower part of the uterus to the outside of the body) and urethra (the tube that carries urine from the bladder to the outside of the body).
These glands are located beside the vaginal opening and produce a fluid (mucus) secretion.
The two labia minora meet at the clitoris, a small, sensitive protrusion that is comparable to the penis in males. The clitoris is covered by a fold of skin, called the prepuce, which is similar to the foreskin at the end of the penis. Like the penis, the clitoris is very sensitive to stimulation and can become erect.
The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. It also is known as the birth canal.
- The uterus is a hollow, pear-shaped organ.
- The uterus is divided into two parts: the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus.
- The corpus can easily expand to hold a developing baby. A channel through the cervix allows sperm to enter and menstrual blood to exit.
- Uterus has three layers:
The endometrium makes up the inner lining of the uterus. It is a mucosal lining and changes in thickness throughout the menstrual cycle.
The myometrium is the middle uterine layer. This is the thickest layer of the uterus. The myometrium is made up of thick smooth muscle tissue.
The perimetrium (or serous coat of uterus) is the outer serosa layer of the uterus, equivalent to peritoneum. It is embrionically derived from visceral peritoneum.
The ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones.
These are narrow tubes that are attached to the upper part of the uterus and serve as tunnels for the ova (egg cells) to travel from the ovaries to the uterus. Conception, the fertilization of an egg by a sperm, normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants into the lining of the uterine wall.
The menstrual cycle is a process that human women go through about every 28 days. During this time, the women’s ovaries create a mature ovum (egg). Then the woman’s body prepares for pregnancy by thickening the walls of the uterus. If the woman does not become pregnant during this time, the egg and the lining of the uterus come out of the woman’s body during menstruation.
The menstrual cycle process is controlled by four major hormones: FSH (follicle stimulating hormone); LH (luteinising hormone); estrogen; and progesterone. These hormones prepare the uterus to receive a fertilized egg and control its development.
The menstrual cycle has three stages: the Follicular stage, Ovulation, and the Luteal (or premenstrual) stage.
- This stage is the start of the menstrual cycle, and is counted as day one of the cycle.
- This stage starts when the amount of progesterone and estrogen in a woman’s blood drop. This causes the endometrium – the thick lining of the uterus – to leave the woman’s body through menstruation.
- It will appear as bleeding from the vagina. This stage lasts from 4–6 days.
- At the start of this stage, the pituitary gland will begin to release more FSH. This will continue for 3-4 days. The FSH makes several follicles grow in one of the ovaries. Each follicle contains an immature ova (egg).
Ovulation happens if rising levels of LH make the ovum mature. The follicle that contains the ovum swells and breaks open. The ovum is released into the Fallopian tube.
The follicle cells that used to hold the ovum now release progesterone into the body. This causes the endometrium to get even thicker.
If the ovum is fertilized during Ovulation, it will become a zygote. It will also move from the ovarian duct into the uterus. The levels of estrogen and progesterone in the body remain high. The zygote grows into an embryo and implants itself into the endometrium tissue of the uterus.
If not fertiized
Until around day 22, estrogen levels increase a little. However, after day 22, the corpus luteum stops making progesterone, and the levels of both progesterone and estrogen in the body start to drop. The amount of progesterone and estrogen in the body are at their lowest around the 28th day of the menstrual cycle.