The female reproductive system consists of external and internal structures. Other anatomic structures that affect the female reproductive system include the hypothalamus and pituitary gland of the endocrine system.
The female reproductive organs release a stored egg (or ovum) at monthly intervals, with two possible outcomes each time: to allow shedding of the uterine lining at menstruation, or to enable fertilization, implantation, and nurture of a developing embryo.
Anatomy and Functions:
The internal structures consist of the vagina, uterus, ovaries, and fallopian or uterine tubes.
The vagina, a canal lined with mucous membrane, is 7.5 to 10 cm (3 to 4 inches) long and extends upward and backward from the vulva to the cervix. Anterior to it are the bladder and the urethra, and posterior to it lies the rectum. The anterior and posterior walls of the vagina normally touch each other. The upper part of the
vagina, the fornix, surrounds the cervix (the inferior part of the uterus).
The uterus, a pear-shaped muscular organ, is about 7.5 cm (3 inches) long and 5 cm (2 inches) wide at its upper part. Its walls are about 1.25 cm (0.5 inch) thick. The size of the uterus varies, depending on parity (number of viable births) and uterine abnormalities (eg, fibroids, which are a type of tumor that may distort the uterus).
The ovaries lie behind the broad ligaments, behind and below the fallopian tubes. They are oval bodies about 3 cm (1.2 inches) long. At birth, they contain thousands of tiny egg cells, or ova. The ovaries and the fallopian tubes together are referred to as the adnexa.
Functions of the Female Reproductive System:
The ovaries are paired, oval organs, each one about the size of an almond, that sit at the ends of the fallopian tubes. Female germ cells (eggs, or ova) mature in the ovaries and are regularly released in a process known as ovulation.
Each month 10 or more follicles, the protective casings surrounding each egg .
start to ripen, but usually just one releases its egg from either the right or the left ovary—right is favored 60 percent of the time. The egg travels down
the fallopian tube to the uterus and is shed from the body along with the uterine lining during the woman’s next menstrual period. If, however, the egg is fertilized in the fallopian tube, the resulting cell mass may implant in the wall of the uterus.
◊An unfertilized egg stays in the reproductive tract for between 12 and 24 hours after ovulation◊
Immature ova are protected within layers of cells called ovarian follicles. The smallest, primordial follicles, have just a single layer of cells. Each month, some of these develop to become mature (Graafian) follicles. Just before ovulation, one mature follicle moves toward the surface of the ovary and bursts through to release its egg.
Its remnants form a body called the corpus luteum and, if the egg is not fertilized, this shrinks to a small, white body called the corpus albicans. At birth, girls have around 1 million follicles per ovary. These will degenerate to about 350,000 by puberty, and 1,500 by menopause.
The Menstrual Cycle:
A menstrual cycle is counted from the first day of menstruation and usually lasts 28–32 days. Just prior to ovulation, which usually occurs on day 14, the uterine lining (endometrium) gradually thickens in preparation for a possible pregnancy. If fertilization does not occur, the outer endometrial layer (functionalis) is shed as menstrual blood. The inner layer (basalis) remains and regenerates the functionalis with each new cycle. If an egg is fertilized, the whole endometrium remains to protect the embryo.
HORMONAL CONTROL: The reproductive cycle is controlled by two hormones from the pituitary gland in the brain. Follicle-stimulating hormone (FSH) causes ovarian follicles to ripen and produce estrogen. When estrogen levels are high enough, a surge of luteinizing hormone (LH) from the pituitary prompts final maturation of the egg and its release from the ovary. After ovulation, as estrogen levels fall, FSH production increases to repeat the cycle.
FUNCTION OF THE CERVIX: The cervix connects the uterus with the vagina and forms a vital barrier to the outside. It secretes mucus that varies in form and function throughout the reproductive cycle. For most of the cycle and during pregnancy, the mucus is thick and sticky to protect the uterus from infection. It also forms an impenetrable barrier to sperm. During a woman’s fertile period, rising levels of estrogen make the mucus thin and stretchy (sort of like egg white), to enable sperm to pass through the cervix and reach the ovulated egg.