The female reproductive tract has two major components: the ovaries, which produce the mature ovum and secrete progestins, androgens, and estrogens,- and the ductal system, which transports ovum, is the place of the union of the sperm and egg, and maintains the developing conceptus until delivery. The morphology and function of these struc tures change in a cyclic manner under the influence of the reproductive hormones.
The ovaries are in the pelvic portion of the abdominal cavity on both sides of the uterus and are anchored by ligaments (Fig. 38.3). An adult ovary weighs 8 to 12 g and consists of an outer cortex and an inner medulla, without a sharp demarcation. The cortex is surrounded by a fibrous tissue, the tunica albuginea, covered by a single layer of surface epithelium continuous with the mesothelium covering the other organs in the abdominal cavity. The cortex contains oocytes enclosed in follicles of various sizes, corpora lutea, corpora al-bicantia, and stromal cells. The medulla contains connective
Early corpus luteum Stroma
and interstitial tissues. Blood vessels, lymphatics, and nerves enter the medulla of the ovary through the hilus.
On the side that ovulates, the oviduct (fallopian tube) receives the ovum immediately after ovulation. The oviducts are the site of fertilization and provide an environment for development of the early embryo. The oviducts are 10 to 15 cm long and composed of sequential regions called the infundibulum, ampulla, and isthmus. The infundibulum is adjacent to the ovary and opens to the peritoneal cavity. It is trumpet-shaped with finger-like projections called fimbria along its outer border that grasp the ovum at the time of follicular rupture. Its thin walls are covered with densely ciliated projections, which facilitate ovum uptake and movement through this region. The ampulla is the site of fertilization. It has a thin musculature and well-developed mucosal surface. The isthmus is located at the uterotubal junction and has a narrow lumen surrounded by smooth muscle. It has sphincter-like properties and can serve as a barrier to the passage of germ cells. The oviducts transport the germ cells in two directions: sperm ascend toward the ampulla and the zygote descends toward the uterus. This requires coordination between smooth muscle contraction, ciliary movement, and fluid secretion, all of which are under hormonal and neuronal control.
The uterus is situated between the urinary bladder and rectum. On each upper side, an oviduct opens into the uterine lumen, and on the lower side, the uterus connects to the vagina. The uterus is composed of two types of tissue. The outer part is the myometrium, composed of multiple layers of smooth muscle. The inner part, lining the lumen of the uterus, is the endometrium, which contains a deep stromal layer next to the myometrium and a superficial epithelial layer. The stroma is permeated by spiral arteries and contains much connective tissue. The epithelial layer is interrupted by uterine glands, which also penetrate the stromal layer and are lined by columnar secretory cells. The uterus provides an environment for the developing fetus, and eventually, the myometrium will generate rhythmic contractions that assist in expelling the fetus at delivery.
The cervix (neck) is a narrow muscular canal that connects the vagina and the body (corpus) of the uterus. It must dilate in response to hormones to allow the expulsion of the fetus. The cervix has numerous glands with a columnar epithelium that produces mucus under the control of estradiol. As more and more estradiol is produced during the follicular phase of the cycle, the cervical mucus changes from a scanty viscous material to a profuse watery and highly elastic substance called spinnbarkeit. The viscosity of the spinnbarkeit can be tested by touching it with a piece of paper and lifting vertically. The mucus can form a thread up to 6 cm under the influence of elevated estradiol. If a drop of the cervical mucus is placed on a slide and allowed to dry, it will form a typical ferning pattern when under the influence of estradiol.
The vagina is well innervated, and has a rich blood supply. It is lined by several layers of epithelium that change histologically during the menstrual cycle. When estradiol levels are low, as during the prepubertal or postmenopausal periods, the vaginal epithelium is thin and the secretions are scanty, resulting in a dry and infection-susceptible area. Estradiol induces proliferation and cornifi-
cation (keratinization) of the vaginal epithelium, whereas progesterone opposes those actions and induces the influx of polymorphonuclear leukocytes into the vaginal fluids. Estradiol also activates vaginal glands that produce lubricating fluid during coitus.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.