The female reproductive system consists of the paired ovaries and fallopian tubes, the uterus, the vagina, and the external genital structures. The egg cells, or ova, are produced in the ovaries and travel though the fallopian tubes to the uterus, where a fertilized ovum can implant and grow. The ovaries produce hormones necessary for the secondary sex characteristics and for maintenance of pregnancy. The breasts or mammary glands are accessory organs of the reproductive system that are able to provide milk for the infant.
FIGURE. Female reproductive system.
The ovaries are oval structures about 1 inch long, each housing several hundred thousand primary follicles present at birth. Close to 400 of these follicles will produce mature ova. The mature follicle responds to LH from the anterior pituitary, causing ovulation. During this time, the ruptured follicle, at this stage called the corpus luteum, secretes progesterone and estrogen. The corpus luteum, now called the ovum, is pulled into one of the two fallopian tubes where it is propelled toward the uterus. The fallopian tubes are each about 4 inches in length and are composed of ciliated epithelial tissue capable of moving the ovum toward the uterus. Fertilization usually occurs in the fallopian tubes; if it does not, the ovum dies within 24 to 48 hours. The fertilized ovum becomes a zygote and is swept into the uterus in about 4 to 5 days.
The uterus is pear shaped, about 3 inches long and 2 inches wide. During pregnancy, the uterus expands significantly to allow the developing fetus to grow. The upper portion of the uterus is called the fundus; the body is the central part, and the cervix is the lower end of the uterus. The two-layer lining of the uterus is the endometrium. One layer is permanent, but the other layer, known as the functional layer, is regenerated and lost during each menstrual cycle. Under the hormonal action of estrogen and progesterone, blood vessel growth thickens the functional layer in preparation for a possible pregnancy. If fertilization does not occur, this layer sloughs off in menstruation. During pregnancy, the endometrium also forms the maternal portion of the placenta.
The vagina is a muscular tube about 4 inches in length that extends from the cervix to the vaginal opening in the perineum. It is posterior to the urethra and anterior to the rectum. The vagina receives the penis and its semen during sexual intercourse, provides the exit for menstrual flow, and is the birth canal at the end of pregnancy. The vulva includes the clitoris, labia majora and minora, and Bartholin glands. The clitoris is erectile tissue that responds to sexual stimulation. The Bartholin glands keep the mucosa of the vagina moist and lubricated during sexual intercourse. Both the labia majora and minora are paired folds of skin on either side of the urethral and vaginal openings that prevent drying of their mucous membranes.
FIGURE. Vulva of female external genitals; inferior view of the perineum. (From Scanlon, VC, and Sanders, T: Essentials of Anatomy and Physiology, ed 5. FA Davis, Philadelphia, 2007, p 467, with permission.)
The breasts or mammary glands produce milk to nourish the infant. After birth, the alveolar glands produce milk that enters the lactiferous ducts on its way to the nipple. Milk formation is dependent on hormone action of prolactin from the anterior pituitary. Also, the infant’s sucking at the nipple stimulates the hypothalamus to send impulses to the posterior pituitary gland to secrete oxytocin, causing the release of milk. The pigmented area around the nipple is called the areola.
FIGURE. The breast. (From Scanlon, VC, and Sanders, T: Essentials of Anatomy and Physiology, ed 5. FA Davis, Philadelphia, 2007, p 467, with permission.)