Female Reproductive System: Functions and Cycles
The Female Reproductive System
The female reproductive system consists of the following organs:
Ovaries
Two ovaries are located on both sides of the body in the abdominal cavity. They are responsible for producing eggs (female gametes or sex cells). The ovaries also produce female sex hormones, regulating the sexual cycle and the development of secondary sexual characteristics in women.
Oviducts (Fallopian Tubes)
These two ducts connect the ovaries to the uterus. Fertilization occurs within the oviducts.
Uterus
The uterus is where implantation of the egg and embryo development occur. The inside is lined by a highly vascular epithelium called the endometrium, which undergoes changes during the menstrual cycle. The uterus has a narrowing called the cervix, which connects with the vagina.
Vagina
The vagina is the tube that connects the uterus to the outside. Its flexible nature allows it to receive the penis during sexual intercourse and dilate for childbirth. The vaginal opening is partially covered by a membrane called the hymen.
Vulva
The vulva is the external part of the female reproductive tract. It consists of two pairs of folds called the labia majora and labia minora. These folds cover the vaginal orifice and the urethra. At the front of the junction of the labia majora is a small erectile organ called the clitoris.
Puberty and Reproduction
During childhood, the reproductive system is inactive. When puberty is reached (usually between 9 and 16 years old), the brain, through the hypothalamus, sends a signal to activate the system.
Differences in male and female sexual organs are known as primary sexual characteristics. These are present at birth and distinguish males from females.
To initiate maturation, the hypothalamus signals the pituitary gland to produce FSH (follicle-stimulating hormone) and LH (luteinizing hormone). These hormones travel through the blood to the sexual organs, stimulating their development and the release of sex hormones that cause internal and external changes.
After puberty, the ovaries begin to produce eggs. This production is controlled by FSH and LH. In girls, these hormones are released at regular intervals as part of the reproductive cycle.
Secondary Sexual Characteristics
In our species, the most important secondary sexual characteristics are:
In women: Growth of underarm and pubic hair, breast development, accumulation of fat in the hips and thighs, and widening of the hips to facilitate delivery.
In men: Growth of facial, armpit, chest, and pubic hair, a deeper voice, and further development of bones and muscles.
The Reproductive Cycle
The female reproductive system undergoes monthly changes to prepare for possible pregnancy. These changes are part of a reproductive cycle with two components: the ovarian cycle and the menstrual cycle.
The Ovarian Cycle
At birth, girls have immature egg cells housed in Graafian follicles within their ovaries.
After puberty, the hypothalamus and pituitary gland send hormonal messages to the ovaries to produce estrogen and progesterone. These hormones stimulate meiosis, and approximately every 28 days, an egg matures in one of the ovaries and is released into the fallopian tube (ovulation).
The Menstrual Cycle
Parallel to the ovarian cycle, the uterine lining (endometrium) thickens to prepare for a fertilized egg. If fertilization doesn’t occur, the endometrium is shed from the uterus and expelled through the vagina along with the unfertilized egg during menstruation (also called menses or period).
The female reproductive cycle proceeds as follows:
Menstruation lasts between three and five days. Simultaneously, the pituitary gland releases FSH, stimulating estrogen secretion and the growth of several follicles in one ovary. Only one follicle reaches maturity, while the others degenerate.
Around day 14, the pituitary gland releases a surge of LH, causing the mature follicle to rupture and release the egg (ovulation). The empty follicle becomes the corpus luteum, which releases progesterone.