 This video will cover the following objective from the reproductive system. Describe the location and structure of the uterine tubes, uterus, vagina, clitoris, and vulva. Describe the three stages of the uterine cycle, menses, proliferative phase, and the secretory phase. Describe the roles of FSH, LH, estrogens, and progesterone in the regulation of the uterine cycle. The external genitalia in women is known as the vulva. The vestibule of the vulva is the region that contains the vaginal opening and the urethral opening. The vestibule of the vulva is located between the labia minora, which are thin, hairless folds of skin, and then there are labia minora, which are the folds of skin forming the lateral borders of the vulva. The clitoris has an external region known as the glands that's located anterior to the urethra in the vulva. There are also internal regions of the clitoris. The bulb of the vestibule is an internal region located deep to the labia surrounding the vagina, and the cruce of the clitoris extends deep along the inferior pubic ramus of the pubic bones. The clitoris becomes engorged with blood during sexual arousal. The clitoris also contains numerous sensory nerve endings responsible for sexual stimulation. The vagina is a muscular tube connecting from the vulva into the uterus, and the inner lining of the vagina is a mucous membrane with a stratified squamous epithelium. The uterus is a pear-shaped organ, and the region of the uterus that connects with the vagina is known as the cervix of the uterus. The uterus is connected to the uterine tubes that transport the oocyte from the ovary, and the uterine tubes are normally the location where fertilization occurs. And then after fertilization, the zygote will continue to develop into an embryo as it moves through the uterine tube and implants into the inner lining of the uterus known as the endometrium, where the embryo will grow and mature into a fetus, and so the uterus will support the maturation of the embryo and fetus until childbirth, when the muscular wall of the uterus can contract in order to force the infant out of the uterus through the vagina. The uterus is stabilized by several ligaments. There's the broad ligament that is an extension of the peritoneal membrane into the pelvic cavity draping along the superior surfaces of the uterus, the uterine tubes, and surrounding the ovaries. Then the round ligaments are extending anteriorly. The round ligaments travel the same pathway through the pelvic cavity to the inguinal canal that the ductus deference travels in males, and this round ligament will anchor the uterus to the anterior wall of the pelvis. This lateral view shows us the relative locations of the uterus, vagina, urinary bladder, and urethra. So the urinary bladder is located just anterior to the uterus, and the urethra connects from the urinary bladder out to the vulva. The urethral opening is just anterior to the vagina. So the vagina connects from the vulva into the cervix of the uterus, and the region of the vagina that surrounds the cervix of the uterus is known as the fornex. The uterine tubes connect into the uterus and function to transport the secondary oocyte after ovulation towards the uterus. Then fertilization will occur inside of the uterine tube, and then the zygote will divide becoming an embryo that will implant into the wall of the uterus. So the inner lining of the uterine tube is a mucous membrane with a ciliated simple columnar epithelium, and the cilia function to help transport the oocyte, sperm, and embryo through the uterine tube. There are three major regions of the uterine tube. The isthmus is the narrow region of the uterine tube attached to the uterus. The ampula is the middle segment of the uterine tube, and is normally the location where fertilization occurs. The infundibulum is the expanded funnel-shaped end of the uterine tube that has numerous finger-like extensions called fimbria that drape around the ovary, the beating of the cilia, as well as peristaltic contractions of the smooth muscle in the wall of the uterine tube, to bring an embryo into the uterus. An embryo will then implant in the inner lining of the uterus known as the endometrium to grow. So the uterus has three layers. The inner layer is the endometrium, a mucous membrane that has two layers to it. So the inner surface of the endometrium is stratum functionalis, and then the lamina propria that anchors the stratum functionalis to the myometrium is known as stratum basalis. And so the basal layer, or stratum basalis, is not shed during menses, and does not have to regrow with each uterine cycle, whereas stratum functionalis regrows during the proliferative phase of the uterine cycle, and then is shed during menstruation. The myometrium is the thick middle layer of the uterus, consisting of smooth muscle and is responsible for the uterine contractions during childbirth. The outer layer of the uterus is the perimetrium, a cirrus membrane, continuous with the broad ligament and the peritoneal membrane. The major regions of the uterus include the body of the uterus, which is the large central compartment of the uterus, and the fundus of the uterus, the superior end of the uterus, just superior to the openings of the uterine tubes, then the inferior narrow region of the uterus is known as the cervix that connects to the vagina. The uterine cycle is a roughly 28 day cycle corresponding to the fluctuations in hormones produced over the ovarian cycle. During the follicular phase of the ovarian cycle, follicle stimulating hormone is stimulating ovarian follicles to start producing estrogen, and estrogen will stimulate proliferation of the stratum functionalis in the endometrium of the uterus, and so this phase of the uterine cycle when the endometrium is growing is known as the proliferative phase of the uterine cycle, when estrogen levels are stimulating that proliferative phase of the uterine cycle. After ovulation, levels of progesterone rise, and progesterone will stimulate the secretory phase of the uterine cycle, so progesterone stimulates the uterine glands to produce secretions and stimulates the maintenance of the stratum functionalis in the endometrium in preparation for implantation of an embryo, but progesterone also has a negative feedback effect to decrease the levels of luteinizing hormone, and as luteinizing hormone levels fall, the corpus luteum will degenerate into corpus albicans and then degrade, causing progesterone levels to decline, and as progesterone levels fall, this will trigger menstruation, the shedding of the stratum functionalis of the endometrium. However, if an embryo does implant into the endometrium, that embryo will start to secrete a hormone known as human chorionic gonadotropin, so the outer layer of cells in the pre-embrio that implants into the endometrium are the trophoblast cells that start to eventually form the placenta. Those cells produce this hormone, human chorionic gonadotropin. Levels of human chorionic gonadotropin rise during the early stages of pregnancy and bind to receptors on cells in the corpus luteum, stimulating the production of progesterone and estrogens. As progesterone levels don't fall during pregnancy, this prevents menstruation, maintaining the endometrium to support the maturation of the embryo into a fetus. Here we see the histology of a fallopian tube, also known as a uterine tube, that has a ciliated columnar epithelium lining the inner mucus membrane, which is then surrounded by a muscularis of smooth muscle. The cilia can beat back and forth to help move a secondary oocyte, or a zygote, or a sperm cell through the uterine tube, and then the smooth muscle in muscularis can perform involuntary waves of contraction that can also facilitate transport through the uterine tube. Here is a higher magnification view of a uterine or fallopian tube with a ciliated columnar epithelium lining the lumen and smooth muscle in the muscularis surrounding that mucus membrane. Here is a view of high magnification focused on the ciliated columnar epithelium lining the mucus membrane of the fallopian tube. Here we see the histology of the uterus at 100 times magnification. The majority of the wall of the uterus is the smooth muscle layer, the myometrium. Adjacent to the myometrium, the deep inner lining of the uterus is a mucus membrane called the endometrium. The endometrium has two layers, a stratum basalis or basal layer adjacent to the myometrium that contains the secretory regions of the uterine ducts and the loose aerial or connective tissue with numerous capillaries that support those glands as well as the epithelium. Stratum functionalis contains the epithelium and the ducts of the uterine glands, and so it's the stratum functionalis that lines the lumen and is shed with menstruation and regrown during the proliferative phase of the uterine cycle.