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LESSON 16

 

Topography and structure of female reproductive organs

 

A woman's reproductive system must produce sex hormones and functional gametes and also be able to protect and support a developing embryo and nourish the newborn infant. The principal organs of the female reproductive system (Figure 28-13 ) are the ovaries, the uterine tubes (Fallopian tubes or oviducts), the uterus, the vagina, and the components of the external genitalia. As in males, a variety of accessory glands secrete into the female reproductive tract.

The ovaries, uterine tubes, and uterus are enclosed within an extensive mesentery known as the broad ligament (Figure 28-14 ). The uterine tubes run along the superior border of the broad ligament and open into the pelvic cavity lateral to the ovaries. The mesovarium, a thickened fold of mesentery, supports and stabilizes the position of each ovary. The broad ligament attaches to the sides and floor of the pelvic cavity, where it becomes continuous with the parietal peritoneum. The broad ligament thus subdivides this part of the peritoneal cavity. The pocket formed between the posterior wall of the uterus and the anterior surface of the colon is the rectouterine pouch; that formed between the uterus and the posterior wall of the bladder is the vesicouterine pouch. These subdivisions are most apparent in sagittal section (Figure 28-13 ).

a

Several other ligaments assist the broad ligament in supporting and stabilizing the position of the uterus and associated reproductive organs. These ligaments lie within the mesentery sheet of the broad ligament and are connected to the ovaries or uterus. The broad ligament limits side-to-side movement and rotation, and the other ligaments (described with the ovaries and uterus) prevent superior-inferior movement.

The Ovaries

The paired ovaries are small, almond-shaped organs located near the lateral walls of the pelvic cavity (Figures 28-13 and 28-14 ). The ovaries (1) produce immature female gametes, or oocytes; (2) secrete female sex hormones, including estrogens and progestins; and (3) secrete inhibin, involved in the feedback control of pituitary FSH production.

The position of each ovary is stabilized by the mesovarium and by a pair of supporting ligaments: the ovarian ligament and the suspensory ligament (Figure 28-14 ). The ovarian ligament extends from the uterus, near the attachment of the uterine tube, to the medial surface of the ovary. The suspensory ligament extends from the lateral surface of the ovary past the open end of the uterine tube to the pelvic wall. The suspensory ligament contains the major blood vessels of the ovary, the ovarian artery and ovarian vein. These vessels are connected to the ovary at the ovarian hilum, where the ovary attaches to the mesovarium.

A typical ovary is a flattened oval that is about 5 cm in length, 2.5 cm in width, and 8 mm in thickness (2 in. x 1 in. x 0.33 in.) and weighs 6-8 g (roughly 0.25 oz). An ovary is pink or yellowish and has a nodular consistency. The visceral peritoneum, or germinal epithelium, covering the surface of each ovary consists of a layer of columnar epthelial cells that overlies a dense connective tissue layer called the tunica albuginea. We can divide the interior tissues, or stroma, of the ovary into a superficial cortex and a deeper medulla. Gametes are produced in the cortex.

Oogenesis

Ovum production, or oogenesis, begins before a woman's birth, accelerates at puberty, and ends at menopause. Between puberty and menopause, oogenesis occurs on a monthly basis as part of the ovarian cycle.

Unlike the situation in the male gonads, the oogonia, or stem cells of females, complete their mitotic divisions before birth. Between the third and seventh months of fetal development, the daughter cells, or primary oocytes, prepare to undergo meiosis. They proceed as far as prophase of meiosis I, but at that time the process comes to a halt. The primary oocytes then remain in a state of suspended development until the individual reaches puberty. At that time, rising levels of FSH trigger the start of the ovarian cycle. Each month thereafter, some of the primary oocytes will be stimulated to undergo further development. Not all primary oocytes produced in development survive until puberty. There are roughly 2 million primordial follicles in the ovaries at birth, each containing a primary oocyte. By the time of puberty, that number has dropped to about 400,000. The rest of the primordial follicles degenerate in a process called atresia.

Although the nuclear events under way during meiosis in the ovaries are the same as those in the testes, the process differs in two important details:

1.                The cytoplasm of the primary oocyte is unevenly distributed during the two meiotic divisions. Oogenesis produces one functional ovum, which contains most of the original cytoplasm, and two or three nonfunctional polar bodies that later disintegrate (Figure 28-15 ).

2.               

3.                The ovary releases a secondary oocyte rather than a mature ovum. The secondary oocyte is suspended in metaphase of meiosis II; meiosis will not be completed unless and until fertilization occurs.

The Ovarian Cycle

Ovarian follicles are specialized structures in which oocyte growth and meiosis I occur. The ovarian follicles are located in the cortex of the ovaries. Primary oocytes are located in the outer portion of the ovarian cortex near the tunica albuginea, in clusters called egg nests. Each primary oocyte within an egg nest is surrounded by a single squamous layer of follicular cells. The primary oocyte and its follicular cells form a primordial follicle. After sexual maturation, a different group of primordial follicles is activated each month. This monthly process is known as the ovarian cycle.

The ovarian cycle can be divided into a follicular phase, or preovulatory phase, and a luteal phase, or postovulatory phase. Important steps in the ovarian cycle can be summarized as follows:

STEP 1: Formation of primary follicles.
Follicle formation is stimulated by FSH from the anterior pituitary. The ovarian cycle begins as activated primordial follicles develop into primary follicles. In a primary follicle, the follicular cells enlarge and undergo repeated cell divisions. The divisions create several layers of follicular cells around the oocyte. These follicle cells are now called granulosa cells.

As layers of granulosa cells develop around the primary oocyte, microvilli from the surrounding granulosa cells intermingle with those of the primary oocyte. The microvilli are surrounded by a layer of glycoproteins, and the entire region is called the zona pellucida. The microvilli increase the surface area available for the transfer of materials from the granulosa cells to the rapidly enlarging oocyte.

The conversion from primordial to primary follicles and subsequent follicular development occurs under FSH stimulation. As the granulosa cells enlarge and multiply, adjacent cells in the ovarian stroma form a layer of thecal cells around the follicle. Thecal cells and granulosa cells work together to produce sex hormones called estrogens.

STEP 2: Formation of secondary follicles.
Although many primordial follicles develop into primary follicles, only a few will proceed to the next step. The transformation begins as the wall of the follicle thickens and the granulosa cells begin secreting small amounts of fluid. This follicular fluid, or liquor folliculi, accumulates in small pockets that gradually expand and separate the inner and outer layers of the follicle. At this stage, the complex is known as a secondary follicle. Although the primary oocyte continues to grow at a steady pace, the follicle as a whole now enlarges rapidly because follicular fluid accumulates.

STEP 3: Formation of a tertiary follicle.
Eight to ten days after the start of the ovarian cycle, the ovaries generally contain only a single secondary follicle destined for further development. By the tenth to fourteenth day of the cycle, that follicle has formed a tertiary follicle, or mature Graafian follicle, roughly 15 mm in diameter. This complex spans the entire width of the ovarian cortex and distorts the ovarian capsule, creating a prominent bulge in the surface of the ovary. The oocyte projects into the expanded central chamber, or antrum, of the follicle surrounded by a mass of granulosa cells.

Until this time, the primary oocyte has been suspended in prophase of the first meiotic division, a state it achieved before birth. As the tertiary follicle completes its development, LH levels begin rising, and the primary oocyte completes meiosis I. Instead of producing two secondary oocytes, the first meiotic division yields a secondary oocyte and a small, nonfunctional polar body. The secondary oocyte then enters meiosis II but stops once again on reaching metaphase. Meiosis II will not be completed unless fertilization occurs.

As the time of ovulation approaches, the secondary oocyte and the surrounding granulosa cells lose their connections with the follicular wall and drift free within the antrum. This event generally occurs on day 14 of a 28-day cycle. The granulosa cells immediately surrounding the secondary oocyte are now known as the corona radiata.

STEP 4: Ovulation.
At ovulation, the tertiary follicle releases the secondary oocyte. The distended follicular wall ruptures, releasing the follicular contents, including the secondary oocyte and corona radiata, into the pelvic cavity. The sticky follicular fluid keeps the corona radiata attached to the surface of the ovary, where direct contact with projections of the uterine tube or with fluid currents established by their ciliated epithelium can transfer the secondary oocyte to the uterine tube.

STEP 5: Formation and degeneration of the corpus luteum.
The empty tertiary follicle initially collapses, and ruptured vessels bleed into the antrum. The remaining granulosa cells then invade the area, proliferating to create an endocrine structure known as the corpus luteum, named for its yellow color (lutea, yellow). This process occurs under LH stimulation.

The lipids contained in the corpus luteum are used to manufacture steroid hormones known as progestins, principally the steroid progesterone. Although moderate amounts of estrogens are also secreted by the corpus luteum, levels are not as high as they were at ovulation, and progesterone is the principal hormone in the interval after ovulation. Its primary function is to prepare the uterus for pregnancy by stimulating the maturation of the uterine lining and the secretions of uterine glands.

STEP 6: Unless pregnancy occurs, the corpus luteum begins to degenerate roughly 12 days after ovulation.
Progesterone and estrogen levels then fall markedly. Fibroblasts invade the nonfunctional corpus luteum, producing a knot of pale scar tissue called a corpus albicans. The disintegration, or involution, of the corpus luteum marks the end of the ovarian cycle. A new cycle then begins with the activation of another group of primordial follicles.

Age and Oogenesis

Although many primordial follicles may have developed into primary follicles, and several primary follicles may have been converted to secondary follicles, generally only a single oocyte will be released into the pelvic cavity at ovulation. The rest undergo atresia. At puberty, there are about 200,000 primordial follicles in each ovary. Forty years later, few if any follicles remain, although only about 500 will have been ovulated during the interim.

The Uterine Tubes

Each uterine tube is a hollow, muscular tube measuring roughly 13 cm (5 in.) in length (Figures 28-13 , sagittal view; 28-14 and 28-17 , posterior views). Each uterine tube is divided into three regions:

1.                The infundibulum. The end closest to the ovary forms an expanded funnel, or infundibulum, with numerous fingerlike projections that extend into the pelvic cavity. The projections are called fimbriae. The inner surfaces of the infundibulum are lined with cilia that beat toward the middle segment of the uterine tube, the ampulla.

2.                The ampulla. The thickness of the smooth muscle layers in the wall of the middle segment, or ampulla, of the uterine tube gradually increases as it approaches the uterus.

3.                The isthmus. The ampulla leads to the isthmus (Figure 28-17b ), a short segment connected to the uterine wall.

Histology of the Uterine Tube

The epithelium lining the uterine tube is composed of ciliated columnar epithelial cells with scattered mucin-secreting cells. The mucosa is surrounded by concentric layers of smooth muscle (Figure 28-17b ). Oocyte transport involves a combination of ciliary movement and peristaltic contractions in the walls of the uterine tube. A few hours before ovulation, sympathetic and parasympathetic nerves from the hypogastric plexus "turn on" this beating pattern. The uterine tubes transport a secondary oocyte for final maturation and fertilization. It normally takes 3-4 days for an oocyte to travel from the infundibulum to the uterine cavity. If fertilization is to occur, the secondary oocyte must encounter spermatozoa during the first 12-24 hours of its passage. Fertilization typically occurs near the boundary between the ampulla and isthmus of the uterine tube.

Along with its transport function, the uterine tube also provides a nutrient-rich environment that contains lipids and glycogen. This mixture provides nutrients to both spermatozoa and a developing pre-embryo (the cell cluster produced by the initial divisions that follow fertilization). Unfertilized oocytes degenerate in the terminal portions of the uterine tubes or within the uterus.

The Uterus

The uterus provides mechanical protection, nutritional support, and waste removal for the developing embryo (weeks 1-8) and fetus (from week 9 to delivery). In addition, contractions in the muscular wall of the uterus are important in ejecting the fetus at the time of birth.

The uterus is a small, pear-shaped organ about 7.5 cm (3 in.) long with a maximum diameter of 5 cm (2 in.). It weighs 30-40 g (1-1.4 oz). In its normal position, the uterus bends anteriorly near its base, a condition known as anteflexion. In this position, the body of the uterus lies across the superior and posterior surfaces of the urinary bladder (Figure 28-13 ). If the uterus bends backward toward the sacrum, the condition is termed retroflexion. Retroflexion, which occurs in about 20 percent of adult women, has no clinical significance. (A retroflexed uterus generally becomes anteflexed spontaneously during the third month of pregnancy.)

Suspensory Ligaments of the Uterus

In addition to the broad ligament, three pairs of suspensory ligaments stabilize the position of the uterus and limit its range of movement (Figure 28-18a,b ). The uterosacral ligaments extend from the lateral surfaces of the uterus to the anterior face of the sacrum, keeping the body of the uterus from moving inferiorly and anteriorly. The round ligaments arise on the lateral margins of the uterus just posterior and inferior to the attachments of the uterine tubes. These ligaments extend through the inguinal canal and end in the connective tissues of the external genitalia. The round ligaments restrict primarily posterior movement of the uterus. The lateral (cardinal) ligaments extend from the base of the uterus and vagina to the lateral walls of the pelvis. These ligaments tend to prevent inferior movement of the uterus. Additional mechanical support is provided by the skeletal muscles and fascia of the pelvic floor.

Internal Anatomy of the Uterus

We can divide the uterus into two anatomical regions (Figure 28-18c ): the body and the cervix. The uterine body, or corpus, is the largest region of the uterus. The fundus is the rounded portion of the body superior to the attachment of the uterine tubes. The body ends at a constriction known as the uterine isthmus. The cervix is the inferior portion of the uterus that extends from the isthmus to the vagina.

The tubular cervix projects about 1.25 cm (0.5 in.) into the vagina. Within the vagina, the distal end of the cervix forms a curving surface that surrounds the cervical os (os, an opening or mouth), or external orifice of the uterus. The cervical os leads into the cervical canal, a constricted passageway that opens into the uterine cavity of the body at the internal os, or internal orifice (Figure 28-18c ).

The uterus receives blood from branches of the uterine arteries, which arise from branches of the internal iliac arteries, and the ovarian arteries, which arise from the abdominal aorta inferior to the renal arteries. There are extensive interconnections among the arteries to the uterus. This arrangement helps ensure a reliable flow of blood to the organ despite changes in position and the changes in uterine shape that accompany pregnancy. Numerous veins and lymphatic vessels also supply each portion of the uterus. The uterus is innervated by autonomic fibers from the hypogastric plexus (sympathetic) and from sacral segments S₃ and S₄ (parasympathetic). Sensory information reaches the CNS within the dorsal roots of spinal nerves T₁₁ and T₁₂. The most delicate anesthetic procedures used during labor and delivery, known as segmental blocks, target only spinal nerves T₁₀-L₁.

The Uterine Wall

The dimensions of the uterus are highly variable. In adult women of reproductive age who have not given birth, the uterine wall is about 1.5 cm (0.5 in.) thick. The uterine wall has a thick, outer, muscular myometrium (myo-, muscle + metra, uterus) and a thin, inner, glandular endometrium, or mucosa. The fundus and the posterior surface of the uterine body and isthmus are covered by a serous membrane continuous with the peritoneal lining. This incomplete serosa is called the perimetrium (Figure 28-18c )

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The endometrium contributes about 10 percent to the mass of the uterus. The glandular and vascular tissues of the endometrium support the physiological demands of the growing fetus. Vast numbers of uterine glands open onto the endometrial surface. These glands extend deep into the lamina propria almost all the way to the myometrium. Under the influence of estrogen, the uterine glands, blood vessels, and epithelium change with the various phases of the monthly uterine cycle.

The myometrium, the thickest portion of the uterine wall, forms almost 90 percent of the mass of the uterus. Smooth muscle in the myometrium is arranged into longitudinal, circular, and oblique layers. The smooth muscle tissue of the myometrium provides much of the force needed to move a large fetus out of the uterus and into the vagina.

The Ovary is a pair organ, is situated in cavity of lesser pelvis. It has medial surface and lateral surface, free margin and mesenteric margin, uterine extremity and tubarius extremity. Ovary is situated in peritoneal cavity, it is covered by embryonic epithelium (not by peritoneum). Ovary attaches to uterus by proper ovaric ligament, and to pelvis walls - by the medium of suspensory ovaric ligament. Ovaric mesentery approaches to anterior margin, through which the vessels and nerves get into ovary hilus. Ovary parenchyma consists of cortex and medulla. Ovule ripens in cortex, where primary folliculi are situated, which then transforms into Graaf vesicle. After that as vesicle blowes up, an oocyte gets out from the ovary and gets into uterine tube. Vesicle becomes as corpus luteum [yellow body]. If there is not fecundation, then corpus luteum transform into corpus albicans. In case of fecundation corpus luteum grows up and turns into corpus luteum verum, which functions during pregnancy.

Uterus and right broad ligament, seen from behind. The broad ligament has been spread out and the ovary drawn downward.

 

 

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The ovaries are homologous with the testes in the male. They are two nodular bodies, situated one on either side of the uterus in relation to the lateral wall of the pelvis, and attached to the back of the broad ligament of the uterus, behind and below the uterine tubes. The ovaries are of a grayish-pink color, and present either a smooth or a puckered uneven surface. They are each about 4 cm. in length, 2 cm. in width, and about 8 mm. in thickness, and weigh from 2 to 3.5 gm. Each ovary presents a lateral and a medial surface, an upper or tubal and a lower or uterine extremity, and an anterior or mesovarion and a posterior free border. It lies in a shallow depression, named the ovarian fossa, on the lateral wall of the pelvis; this fossa is bounded above by the external iliac vessels, in front by the obliterated umbilical artery, and behind by the ureter. The exact position of the ovary has been the subject of considerable difference of opinion, and the description here given applies to the ovary of the nulliparous woman. The ovary becomes displaced during the first pregnancy, and probably never again returns to its original position. In the erect posture the long axis of the ovary is vertical. The tubal extremity is near the external iliac vein; to it are attached the ovarian fimbria of the uterine tube and a fold of peritoneum, the suspensory ligament of the ovary, which is directed upward over the iliac vessels and contains the ovarian vessels. The uterine end is directed downward toward the pelvic floor, it is usually narrower than the tubal, and is attached to the lateral angle of the uterus, immediately behind the uterine tube, by a rounded cord termed the ligament of the ovary, which lies within the broad ligament and contains some non-striped, muscular fibers. The lateral surface is in contact with the parietal peritoneum, which lines the ovarian fossa; the medial surface is to a large extent covered by the fimbriated extremity of the uterine tube. The mesovarian border is straight and is directed toward the obliterated umbilical artery, and is attached to the back of the broad ligament by a short fold named the mesovarium. Between the two layers of this fold the bloodvessels and nerves pass to reach the hilum of the ovary. The free border is convex, and is directed toward the ureter. The uterine tube arches over the ovary, running upward in relation to its mesovarian border, then curving over its tubal pole, and finally passing downward on its free border and medial surface.

 

 

Adult ovary, epoöphoron, and uterine tube. (From Farre, after Kobelt.) a, a. Epoöphoron formed from the upper part of the Wolffian body. b. Remains of the uppermost tubes sometimes forming hydatids. c. Middle set of tubes. d. Some lower atrophied tubes. e. Atrophied remains of the Wolffian duct. f. The terminal bulb or hydatid. h. The uterine tube. i. Hydatid attached to the extremity. l. The ovary.

 

Epoöphoron (parovarium; organ of Rosenmüller) lies in the mesosalpinx between the ovary and the uterine tube, and consists of a few short tubules (ductuli transversi) which converge toward the ovary while their opposite ends open into a rudimentary duct, the ductus longitudinalis epoöphori (duct of Gärtner).

 

Paroöphoron.—The paroöphoron consists of a few scattered rudimentary tubules, best seen in the child, situated in the broad ligament between the epoöphoron and the uterus.

  The ductuli transversi of the epoophoron and the tubules of the paroophoron are remnants of the tubules of the Wolffian body or mesonephros; the ductus longitudinalis epoöphori is a persistent portion of the Wolffian duct.

  In the fetus the ovaries are situated, like the testes, in the lumbar region, near the kidneys, but they gradually descend into the pelvis.

 

Section of the ovary. (After Schrön.) 1. Outer covering. 1’. Attached border. 2. Central stroma. 3. Peripheral stroma. 4. Bloodvessels. 5. Vesicular follicles in their earliest stage. 6, 7, 8. More advanced follicles. 9. An almost mature follicle. 9’. Follicle from which the ovum has escaped. 10. Corpus luteum.

 

 

 

Structure. The surface of the ovary is covered by a layer of columnar cells which constitutes the germinal epithelium of Waldeyer. This epithelium gives to the ovary a dull gray color as compared with the shining smoothness of the peritoneum; and the transition between the squamous epithelium of the peritoneum and the columnar cells which cover the ovary is usually marked by a line around the anterior border of the ovary. The ovary consists of a number of vesicular ovarian follicles imbedded in the meshes of a stroma or frame-work.

  The stroma is a peculiar soft tissue, abundantly supplied with bloodvessels, consisting for the most part of spindle-shaped cells with a small amount of ordinary connective tissue. These cells have been regarded by some anatomists as unstriped muscle cells, which, indeed, they most resemble; by others as connective-tissue cells. On the surface of the organ this tissue is much condensed, and forms a layer (tunica albuginea) composed of short connective-tissue fibers, with fusiform cells between them. The stroma of the ovary may contain interstitial cells resembling those of the testis.

 

Vesicular Ovarian Follicles (Graafian follicles).—Upon making a section of an ovary, numerous round transparent vesicles of various sizes are to be seen; they are the follicles, or ovisacs containing the ova. Immediately beneath the superficial covering is a layer of stroma, in which are a large number of minute vesicles, of uniform size, about 0.25 mm. in diameter. These are the follicles in their earliest condition, and the layer where they are found has been termed the cortical layer. They are especially numerous in the ovary of the young child. After puberty, and during the whole of the child-bearing period, large and mature, or almost mature follicles are also found in the cortical layer in small numbers, and also “corpora lutea,” the remains of follicles which have burst and are undergoing atrophy and absorption. Beneath this superficial stratum, other large and more or less mature follicles are found imbedded in the ovarian stroma. These increase in size as they recede from the surface toward a highly vascular stroma in the center of the organ, termed the medullary substance (zona vasculosa of Waldeyer). This stroma forms the tissue of the hilum by which the ovary is attached, and through which the bloodvessels enter: it does not contain any follicles.

  The larger follicles consist of an external fibrovascular coat, connected with the surrounding stroma of the ovary by a net-work of bloodvessels; and an internal coat, which consists of several layers of nucleated cells, called the membrana granulosa. At one part of the mature follicle the cells of the membrana granulosa are collected into a mass which projects into the cavity of the follicle. This is termed the discus proligerus, and in it the ovum is imbedded. The follicle contains a transparent albuminous fluid.

  The development and maturation of the follicles and ova continue uninterruptedly from puberty to the end of the fruitful period of woman’s life, while their formation commences before birth. Before puberty the ovaries are small and the follicles contained in them are disposed in a comparatively thick layer in the cortical substance; here they present the appearance of a large number of minute closed vesicles, constituting the early condition of the follicles; many, however, never attain full development, but shrink and disappear. At puberty the ovaries enlarge and become more vascular, the follicles are developed in greater abundance, and their ova are capable of fecundation.

 

Section of vesicular ovarian follicle

 

Discharge of the Ovum.—The follicles, after attaining a certain stage of development, gradually approach the surface of the ovary and burst; the ovum and fluid contents of the follicle are liberated on the exterior of the ovary, and carried into the uterine tube by currents set up by the movements of the cilia covering the mucous membrane of the fimbriae.

 

Corpus Luteum.—After the discharge of the ovum the lining of the follicle is thrown into folds, and vascular processes grow inward from the surrounding tissue. In this way the space is filled up and the corpus luteum formed. It consists at first of a radial arrangement of yellow cells with bloodvessels and lymphatic spaces, and later it merges with the surrounding stroma.

 

Vessels and Nerves.—The arteries of the ovaries and uterine tubes are the ovarian from the aorta. Each anastomoses freely in the mesosalpinx, with the uterine artery, giving some branches to the uterine tube, and others which traverse the mesovarium and enter the hilum of the ovary. The veins emerge from the hilum in the form of a plexus, the pampiniform plexus; the ovarian vein is formed from this plexus, and leaves the pelvis in company with the artery. The nerves are derived from the hypogastric or pelvic plexus, and from the ovarian plexus, the uterine tube receiving a branch from one of the uterine nerves.

 

The Uterine tube is a pair organ is situated in area of superior margin of ligamentum latum uteri. Length of each tube is 8-18 cm. There are 4 parts:

§  uterine part runs in wall of uterus and opens into uterine cavity by uterine ostium;

§  isthmus of uterine tube lies closely to uterus;

§  ampulla of uterine tube is greater part of uterine tube;

§  infundibulum of uterine tube - is broadened part, which opens by abdominal foramen of uterine tube into abdominal (peritoneal) cavity and covered by fimbria, one of which - ovaric fimbria is longer then other.

Uterine tube is covered from all sides by peritoneum and has its own mesentery. Tube has also muscular membrane (longitudinal and circular layers) and mucous membrane. Fecundation realizes in uterine tube normally, than fertilized ovule passes into uterus.

Female pelvis and its contents, seen from above and in front.

 

The Uterus is an odd hollow organ, pear-shaped object, which is situated in cavity of lesser pelvis. It has a fundus, body and neck of uterus, which opens into vagina by uterine ostium, limited by anterior labium and posterior labium. Uterine neck divided into supravaginal portion and vaginal portion. Uterine body has vesical surface (anterior) and intestinal surface (posterior). Place of transition body of uterus into neck is called as isthmus. Anterior uterus surface adjoins to urinary bladder, and posterior - to rectum. Attached to empty urinary bladder body of uterus is tilted forward. Such position is called anteversio. Attached to full urinary bladder a fundus and uterus body displaces posteriorly – this is retroversio. Also between body and uterus neck is formed a angle, open forward. Such position is called anteflexio.

Triangle-shaped cavity of uterus above communicate with uterine tubes, and vagina through the cervical canal and ostium uteri.

Wall of uterus consists of three layers:

• mucous membrane (endometrium), submucous stratum is absent ,so there is no folds on internal surface of uterus;

• muscular membrane (myometrium) is formed by smooth muscle and consists of internal, middle and external layers;

• serous membrane (perimetrium) is a peritoneum, which covers an uterus from all sides, except part of front surface and lateral margins and supravaginal portion of neck (mesoperitoneal position). Serous membrane forms ligamentum uteri latum, which forms mesentery of uterus, mesentery of ovary and mesentery of uterine tube. Between sheets of ligamentum latum uteri the vessels, nerves, adipose tissue (parametrium) and ligamentum teres uteri are contained. Ligamentum teres [round] uteri passes through the inguinal canal to pubis. Also uterus is fixed to pelvic walls by cardinal ligament.

The uterus is a hollow, thick-walled, muscular organ situated deeply in the pelvic cavity between the bladder and rectum. Into its upper part the uterine tubes open, one on either side, while below, its cavity communicates with that of the vagina. When the ova are discharged from the ovaries they are carried to the uterine cavity through the uterine tubes. If an ovum be fertilized it imbeds itself in the uterine wall and is normally retained in the uterus until prenatal development is completed, the uterus undergoing changes in size and structure to accommodate itself to the needs of the growing embryo (see page 59). After parturition the uterus returns almost to its former condition, but certain traces of its enlargement remains. It is necessary, therefore, to describe as the type-form the adult virgin uterus, and then to consider the modifications which are effected as a result of pregnancy.

 

Sagittal section of the lower part of a female trunk, right segment. SM. INT. Small intestine

 

  In the virgin state the uterus is flattened antero-posteriorly and is pyriform in shape, with the apex directed downward and backward. It lies between the bladder in front and the pelvic or sigmoid colon and rectum behind, and is completely within the pelvis, so that its base is below the level of the superior pelvic aperture. Its upper part is suspended by the broad and the round ligaments, while its lower portion is imbedded in the fibrous tissue of the pelvis.

  The long axis of the uterus usually lies approximately in the axis of the superior pelvic aperture, but as the organ is freely movable its position varies with the state of distension of the bladder and rectum. Except when much displaced by a fully distended bladder, it forms a forward angle with the vagina, since the axis of the vagina corresponds to the axes of the cavity and inferior aperture of the pelvis.

  The uterus measures about 7.5 cm. in length, 5 cm. in breadth, at its upper part, and nearly 2.5 cm. in thickness; it weighs from 30 to 40 gm. It is divisible into two portions. On the surface, about midway between the apex and base, is a slight constriction, known as the isthmus, and corresponding to this in the interior is a narrowing of the uterine cavity, the internal orifice of the uterus. The portion above the isthmus is termed the body, and that below, the cervix. The part of the body which lies above a plane passing through the points of entrance of the uterine tubes is known as the fundus.

 

Body (corpus uteri).—The body gradually narrows from the fundus to the isthmus.

  The vesical or anterior surface (facies vesicalis) is flattened and covered by peritoneum, which is reflected on to the bladder to form the vesicouterine excavation. The surface lies in apposition with the bladder.

  The intestinal or posterior surface (facies intestinalis) is convex transversely and is covered by peritoneum, which is continued down on to the cervix and vagina. It is in relation with the sigmoid colon, from which it is usually separated by some coils of small intestine.

  The fundus (fundus uteri) is convex in all directions, and covered by peritoneum continuous with that on the vesical and intestinal surfaces. On it rest some coils of small intestine, and occasionally the distended sigmoid colon.

  The lateral margins (margo lateralis) are slightly convex. At the upper end of each the uterine tube pierces the uterine wall. Below and in front of this point the round ligament of the uterus is fixed, while behind it is the attachment of the ligament of the ovary. These three structures lie within a fold of peritoneum which is reflected from the margin of the uterus to the wall of the pelvis, and is named the broad ligament.

 

Cervix (cervix uteri; neck).—The cervix is the lower constricted segment of the uterus. It is somewhat conical in shape, with its truncated apex directed downward and backward, but is slightly wider in the middle than either above or below. Owing to its relationships, it is less freely movable than the body, so that the latter may bend on it. The long axis of the cervix is therefore seldom in the same straight line as the long axis of the body. The long axis of the uterus as a whole presents the form of a curved line with its concavity forward, or in extreme cases may present an angular bend at the region of the isthmus.

  The cervix projects through the anterior wall of the vagina, which divides it into an upper, supravaginal portion, and a lower, vaginal portion.

  The supravaginal portion (portio supravaginalis [cervicis]) is separated in front from the bladder by fibrous tissue (parametrium), which extends also on to its sides and lateralward between the layers of the broad ligaments. The uterine arteries reach the margins of the cervix in this fibrous tissue, while on either side the ureter runs downward and forward in it at a distance of about 2 cm. from the cervix. Posteriorly, the supravaginal cervix is covered by peritoneum, which is prolonged below on to the posterior vaginal wall, when it is reflected on to the rectum, forming the rectouterine excavation. It is in relation with the rectum, from which it may be separated by coils of small intestine.

  The vaginal portion (portio vaginalis [cervicis]) of the cervix projects free into the anterior wall of the vagina between the anterior and posterior fornices. On its rounded extremity is a small, depressed, somewhat circular aperture, the external orifice of the uterus, through which the cavity of the cervix communicates with that of the vagina. The external orifice is bounded by two lips, an anterior and a posterior, of which the anterior is the shorter and thicker, although, on account of the slope of the cervix, it projects lower than the posterior. Normally, both lips are in contact with the posterior vaginal wall.

 

Interior of the Uterus—The cavity of the uterus is small in comparison with the size of the organ.

  The Cavity of the Body (cavum uteri) is a mere slit, flattened antero-posteriorly. It is triangular in shape, the base being formed by the internal surface of the fundus between the orifices of the uterine tubes, the apex by the internal orifice of the uterus through which the cavity of the body communicates with the canal of the cervix.

  The Canal of the Cervix (canalis cervicis uteri) is somewhat fusiform, flattened from before backward, and broader at the middle than at either extremity. It communicates above through the internal orifice with the cavity of the body, and below through the external orifice with the vaginal cavity. The wall of the canal presents an anterior and a posterior longitudinal ridge, from each of which proceed a number of small oblique columns, the palmate folds, giving the appearance of branches from the stem of a tree; to this arrangement the name arbor vitae uterina is applied. The folds on the two walls are not exactly opposed, but fit between one another so as to close the cervical canal.

 

 

Posterior half of uterus and upper part of vagina.

 

  The total length of the uterine cavity from the external orifice to the fundus is about 6.25 cm.

 Ligaments.—The ligaments of the uterus are eight in number: one anterior; one posterior; two lateral or broad; two uterosacral; and two round ligaments.

  The anterior ligament consists of the vesicouterine fold of peritoneum, which is reflected on to the bladder from the front of the uterus, at the junction of the cervix and body.

  The posterior ligament consists of the rectovaginal fold of peritoneum, which is reflected from the back of the posterior fornix of the vagina on to the front of the rectum. It forms the bottom of a deep pouch called the rectouterine excavation, which is bounded in front by the posterior wall of the uterus, the supravaginal cervix, and the posterior fornix of the vagina; behind, by the rectum; and laterally by two crescentic folds of peritoneum which pass backward from the cervix uteri on either side of the rectum to the posterior wall of the pelvis. These folds are named the sacrogenital or rectouterine folds. They contain a considerable amount of fibrous tissue and non-striped muscular fibers which are attached to the front of the sacrum and constitute the uterosacral ligaments.

  The two lateral or broad ligaments (ligamentum latum uteri) pass from the sides of the uterus to the lateral walls of the pelvis. Together with the uterus they form a septum across the female pelvis, dividing that cavity into two portions. In the anterior part is contained the bladder; in the posterior part the rectum, and in certain conditions some coils of the small intestine and a part of the sigmoid colon. Between the two layers of each broad ligament are contained: (1) the uterine tube superiorly; (2) the round ligament of the uterus; (3) the ovary and its ligament; (4) the epoöphoron and paroöphoron; (5) connective tissue; (6) unstriped muscular fibers; and (7) bloodvessels and nerves. The portion of the broad ligament which stretches from the uterine tube to the level of the ovary is known by the name of the mesosalpinx. Between the fimbriated extremity of the tube and the lower attachment of the broad ligament is a concave rounded margin, called the infundibulopelvic ligament.

  The round ligaments (ligamentum teres uteri) are two flattened bands between 10 and 12 cm. in length, situated between the layers of the broad ligament in front of and below the uterine tubes. Commencing on either side at the lateral angle of the uterus, this ligament is directed forward, upward, and lateralward over the external iliac vessels. It then passes through the abdominal inguinal ring and along the inguinal canal to the labium majus, in which it becomes lost. The round ligaments consists principally of muscular tissue, prolonged from the uterus; also of some fibrous and areolar tissue, besides bloodvessels, lymphatics; and nerves, enclosed in a duplicature of peritoneum, which, in the fetus, is prolonged in the form of a tubular process for a short distance into the inguinal canal. This process is called the canal of Nuck. It is generally obliterated in the adult, but sometimes remains pervious even in advanced life. It is analogous to the saccus vaginalis, which precedes the descent of the testis.

  In addition to the ligaments just described, there is a band named the ligamentum transversalis colli (Mackenrodt) on either side of the cervix uteri. It is attached to the side of the cervix uteri and to the vault and lateral fornix of the vagina, and is continuous externally with the fibrous tissue which surrounds the pelvic bloodvessels.

  The form, size, and situation of the uterus vary at different periods of life and under different circumstances.

 

Sagittal section through the pelvis of a newly born female.

 

  In the fetus the uterus is contained in the abdominal cavity, projecting beyond the superior aperture of the pelvis. The cervix is considerably larger than the body.

  At puberty the uterus is pyriform in shape, and weighs from 14 to 17 gm. It has descended into the pelvis, the fundus being just below the level of the superior aperture of this cavity. The palmate folds are distinct, and extend to the upper part of the cavity of the organ.

  The position of the uterus in the adult is liable to considerable variation, depending chiefly on the condition of the bladder and rectum. When the bladder is empty the entire uterus is directed forward, and is at the same time bent on itself at the junction of the body and cervix, so that the body lies upon the bladder. As the latter fills, the uterus gradually becomes more and more erect, until with a fully distended bladder the fundus may be directed backward toward the sacrum.

  During menstruation the organ is enlarged, more vascular, and its surfaces rounder; the external orifice is rounded, its labia swollen, and the lining membrane of the body thickened, softer, and of a darker color. According to Sir J. Williams, at each recurrence of menstruation, a molecular disintegration of the mucous membrane takes place, which leads to its complete removal, only the bases of the glands imbedded in the muscle being left. At the cessation of menstruation, a fresh mucous membrane is formed by a proliferation of the remaining structures.

  During pregnancy the uterus becomes enormously enlarged, and in the eighth month reaches the epigastric region. The increase in size is partly due to growth of preëxisting muscle, and partly to development of new fibers.

  After parturition the uterus nearly regains its usual size, weighing about 42 gm.; but its cavity is larger than in the virgin state, its vessels are tortuous, and its muscular layers are more defined; the external orifice is more marked, and its edges present one or more fissures.

  In old age the uterus becomes atrophied, and paler and denser in texture; a more distinct constriction separates the body and cervix. The internal orifice is frequently, and the external orifice occasionally, obliterated, while the lips almost entirely disappear.

 

Structure.—The uterus is composed of three coats: an external or serous, a middle or muscular, and an internal or mucous.

  The serous coat (tunica serosa) is derived from the peritoneum; it invests the fundus and the whole of the intestinal surface of the uterus; but covers the vesical surface only as far as the junction of the body and cervix. In the lower fourth of the intestinal surface the peritoneum, though covering the uterus, is not closely connected with it, being separated from it by a layer of loose cellular tissue and some large veins.

  The muscular coat (tunica muscularis) forms the chief bulk of the substance of the uterus. In the virgin it is dense, firm, of a grayish color, and cuts almost like cartilage. It is thick opposite the middle of the body and fundus, and thin at the orifices of the uterine tubes. It consists of bundles of unstriped muscular fibers, disposed in layers, intermixed with areolar tissue, bloodvessels, lymphatic vessels, and nerves. The layers are three in number: external, middle, and internal. The external and middle layers constitute the muscular coat proper, while the inner layer is a greatly hypertrophied muscularis mucosae. During pregnancy the muscular tissue becomes more prominently developed, the fibers being greatly enlarged.

  The external layer, placed beneath the peritoneum, is disposed as a thin plane on the vesical and intestinal surfaces. It consists of fibers which pass transversely across the fundus, and, converging at each lateral angle of the uterus, are continued on to the uterine tube, the round ligament, and the ligament of the ovary: some passing at each side into the broad ligament, and others running backward from the cervix into the sacrouterine ligaments. The middle layer of fibers presents no regularity in its arrangement, being disposed longitudinally, obliquely, and transversely. It contains more bloodvessels than either of the other two layers. The internal or deep layer consists of circular fibers arranged in the form of two hollow cones, the apices of which surround the orifices of the uterine tubes, their bases intermingling with one another on the middle of the body of the uterus. At the internal orifice these circular fibers form a distinct sphincter.

  The mucous membrane (tunica mucosa) is smooth, and closely adherent to the subjacent tissue. It is continuous through the fimbriated extremity of the uterine tubes, with the peritoneum; and, through the external uterine orifice, with the lining of the vagina.

  In the body of the uterus the mucous membrane is smooth, soft, of a pale red color, lined by columnar ciliated epithelium, and presents, when viewed with a lens, the orifices of numerous tubular follicles, arranged perpendicularly to the surface. The structure of the corium differs from that of ordinary mucous membranes, and consists of an embryonic nucleated and highly cellular form of connective tissue in which run numerous large lymphatics. In it are the tube-like uterine glands, lined by ciliated columnar epithelium. They are of small size in the unimpregnated uterus, but shortly after impregnation become enlarged and elongated, presenting a contorted or waved appearance (see page 60).

 

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  In the cervix the mucous membrane is sharply differentiated from that of the uterine cavity. It is thrown into numerous oblique ridges, which diverge from an anterior and posterior longitudinal raphé. In the upper two-thirds of the canal, the mucous membrane is provided with numerous deep glandular follicles, which secrete a clear viscid alkaline mucus; and, in addition, extending through the whole length of the canal is a variable number of little cysts, presumably follicles which have become occluded and distended with retained secretion. They are called the ovula Nabothi. The mucous membrane covering the lower half of the cervical canal presents numerous papillae. The epithelium of the upper two-thirds is cylindrical and ciliated, but below this it loses its cilia, and gradually changes to stratified squamous epithelium close to the external orifice. On the vaginal surface of the cervix the epithelium is similar to that lining the vagina, viz., stratified squamous.

 

The arteries of the internal organs of generation of the female, seen from behind.

 

Vessels and Nerves.—The arteries of the uterus are the uterine, from the hypogastric; and the ovarian, from the abdominal aorta.  They are remarkable for their tortuous course in the substance of the organ, and for their frequent anastomoses. The termination of the ovarian artery meets that of the uterine artery, and forms an anastomotic trunk from which branches are given off to supply the uterus, their disposition being circular.

Histology of the Uterus
We can divide the endometrium into (1) a functional zone, the layer closest to the uterine cavity, and (2) an outer basilar zone adjacent to the myometrium. The functional zone contains most of the uterine glands and contributes most of the endometrial thickness. The basilar zone attaches the endometrium to the myometrium and contains the terminal branches of the tubular glands.

Within the myometrium, branches of the uterine arteries form arcuate arteries that encircle the endometrium. Radial arteries supply straight arteries that deliver blood to the basilar zone of the endometrium and spiral arteries that supply the functional zone (Figure 28-19 ).

The structure of the basilar zone remains relatively constant over time, but that of the functional zone undergoes cyclical changes in response to sex hormone levels. These cyclical changes produce the characteristic histological features of the uterine cycle.

The Uterine Cycle

The uterine cycle, or menstrual cycle, is a repeating series of changes in the structure of the endometrium. The uterine cycle averages 28 days in length, but it can range from 21 to 35 days in healthy women of reproductive age. We can divide the cycle into three phases: (1) menses, (2) the proliferative phase, and (3) the secretory phase. The histological appearance of the endometrium during each phase is shown in Figure 28-20 . The phases occur in response to hormones associated with the regulation of the ovarian cycle. Menses and the proliferative phase occur during the follicular phase of the ovarian cycle. The secretory phase corresponds to the luteal phase of the ovarian cycle. We shall consider the regulatory mechanism in a later section.

Menses
The uterine cycle begins with the onset of menses, an interval marked by the degeneration of the functional zone of the endometrium. The deterioration occurs in patches. It is caused by the constriction of the spiral arteries, which reduces blood flow to areas of endometrium. Deprived of oxygen and nutrients, the secretory glands and other tissues in the functional zone begin to deteriorate. Eventually, the weakened arterial walls rupture, and blood pours into the connective tissues of the functional zone. Blood cells and degenerating tissues then break away and enter the uterine lumen, to be lost by passage through the cervical os and into the vagina. Only the functional zone is affected, because the deeper, basilar zone is provided with blood from the straight arteries, which remain unconstricted.

The sloughing of tissue is gradual, and at each site, repairs begin almost at once. Nevertheless, before menses has ended, the entire functional zone has been lost (Figure 28-20a ). This process of endometrial sloughing is called menstruation. Menstruation generally lasts from 1 to 7 days, and over this period roughly 35 to 50 ml of blood is lost. The process can be relatively painless. Painful menstruation, or dysmenorrhea, can result from uterine inflammation and contraction or from conditions involving adjacent pelvic structures.

The Proliferative Phase
The basilar zone, including the basal portions of the uterine glands, survives menses intact. In the days following the completion of menses, the epithelial cells of the glands multiply and spread across the endometrial surface, restoring the integrity of the uterine epithelium (Figure 28-20b ). Further growth and vascularization result in the complete restoration of the functional zone. As this reorganization proceeds, the endometrium is said to be in the proliferative phase. This restoration occurs at the same time as the enlargement of primary and secondary follicles in the ovary. The proliferative phase is stimulated and sustained by estrogens secreted by the developing ovarian follicles.

By the time ovulation occurs, the functional zone is several millimeters thick, and prominent mucous glands extend to the border with the basilar zone. At this time, the endometrial glands are manufacturing a mucus rich in glycogen. The entire functional zone is highly vascularized, with small arteries spiraling toward the inner surface from larger arteries in the myometrium.

The Secretory Phase
During the secretory phase of the uterine cycle, the endometrial glands enlarge, accelerating their rates of secretion, and the arteries elongate and spiral through the tissues of the functional zone . This activity occurs under the combined stimulatory effects of progestins and estrogens from the corpus luteum. This phase begins at the time of ovulation and persists as long as the corpus luteum remains intact.

Secretory activities peak about 12 days after ovulation. Over the next day or two, the glandular activity declines, and the uterine cycle comes to a close as the corpus luteum stops producing stimulatory hormones. A new cycle then begins with the onset of menses and the disintegration of the functional zone. The secretory phase generally lasts 14 days. As a result, you can determine the date of ovulation after the fact, by counting backward 14 days from the first day of menses.

Menarche and Menopause
The uterine cycle begins with the menarche, or first menstrual period at puberty, typically at age 11-12. The cycles continue until age 45-55, when menopause, the last uterine cycle, occurs. Over the intervening three and a half to four decades, the regular appearance of uterine cycles is interrupted only by unusual circumstances, such as illness, stress, starvation, or pregnancy.

If menarche does not appear by age 16, or if the normal uterine cycle of an adult woman becomes interrupted for 6 months or more, the condition of amenorrhea exists. Primary amenorrhea is the failure to initiate menses. This condition may indicate developmental abnormalities, such as nonfunctional ovaries, the absence of a uterus, or an endocrine or genetic disorder. Transient secondary amenorrhea may be caused by severe physical or emotional stresses. In effect, the reproductive system gets "switched off" under these conditions. Examples of factors that can cause amenorrhea include drastic weight-reduction programs, anorexia nervosa, and severe depression or grief. Amenorrhea has also been observed in marathon runners and other women engaged in training programs that require sustained high levels of exertion and severely reduce body lipid reserves.

The Vagina

The vagina is an elastic, muscular tube. It extends between the cervix of the uterus and the vestibule, a space bounded by the female external genitalia (Figures 28-13 and 28-14 ). The vagina has an average length of 7.5-9 cm (3-3.5 in.), but because the vagina is highly distensible, its length and width vary.

At the proximal end of the vagina, the cervix projects into the vaginal canal. The shallow recess surrounding the cervical protrusion is known as the fornix. The vagina lies parallel to the rectum, and the two are in close contact posteriorly. Anteriorly, the urethra extends along the superior wall of the vagina from the urinary bladder to the external urethral meatus, which opens into the vestibule. The primary blood supply of the vagina is via the vaginal branches of the internal iliac (or uterine) arteries and veins. Innervation is from the hypogastric plexus, sacral nerves S₂-S₄, and branches of the pudendal nerve.

The vagina has three major functions:

1.                It serves as a passageway for the elimination of menstrual fluids.

2.                It receives the penis during sexual intercourse and holds spermatozoa prior to their passage into the uterus.

3.                It forms the lower portion of the birth canal, through which the fetus passes during delivery.

4.               

Histology of the Vagina

In sectional view, the lumen of the vagina appears constricted, forming a rough H. The vaginal walls contain a network of blood vessels and layers of smooth muscle. The lining is moistened by the secretions of the cervical glands and by the movement of water across the permeable epithelium. The vagina and vestibule are separated by the hymen, an elastic epithelial fold that partially or completely blocks the entrance to the vagina before the onset of sexual intercourse. The two bulbospongiosus muscles extend along either side of the vaginal entrance, and their contractions constrict the entrance, (Figure 11-13a ). These muscles cover the vestibular bulbs, masses of erectile tissue on either side of the vaginal entrance. The vestibular bulbs have the same embryological origins as the corpus spongiosum of the penis in the male.

The vaginal lumen is lined by a nonkeratinized stratified squamous epithelium that in the relaxed state is thrown into folds called rugae. The underlying lamina propria is thick and elastic, and it contains small blood vessels, nerves, and lymph nodes. The vaginal mucosa is surrounded by an elastic muscularis layer, with layers of smooth muscle fibers arranged in circular and longitudinal bundles continuous with the uterine myometrium. The portion of the vagina adjacent to the uterus has a serosal covering continuous with the pelvic peritoneum. Along the rest of the vagina, the muscularis layer is surrounded by an adventitia of fibrous connective tissue.

The vagina contains a population of resident bacteria, usually harmless, supported by nutrients in the cervical mucus. The metabolic activity of these bacteria creates an acidic environment, which restricts the growth of many pathogens. An inflammation of the vaginal canal, known as vaginitis, is caused by fungi, bacteria, or parasites. In addition to any discomfort that may result, the condition may affect the survival of sperm and thereby reduce fertility.

An acidic environment also inhibits sperm motility; for this reason, the buffers in semen are important to successful fertilization.

The hormonal changes associated with the ovarian cycle also have an effect on the vaginal epithelium. A vaginal smear is a sample of epithelial cells shed at the vaginal surface. By examining these cells, a clinician can estimate the corresponding stage in the ovarian and uterine cycles. This technique is an example of exfoliative cytology.

The External Genitalia

The region containing the female external genitalia is the vulva, or pudendum (Figure 28-22 ). The vagina opens into the vestibule, a central space bounded by small folds known as the labia minora (singular, labium minus). The labia minora are covered with a smooth, hairless skin. The urethra opens into the vestibule just anterior to the vaginal entrance. The paraurethral glands, or Skene's glands, discharge into the urethra near the external urethral opening. Anterior to the urethral opening, the clitoris projects into the vestibule. The clitoris, a small, rounded tissue projection, is the female equivalent of the penis; it is derived from the same embryonic structures. Internally, it contains erectile tissue comparable to the corpora cavernosa of the penis. The clitoris engorges with blood during sexual arousal. A small erectile glans sits atop the organ; extensions of the labia minora encircle the body of the clitoris, forming the prepuce, or hood, of the clitoris.

A variable number of small lesser vestibular glands discharge their secretions onto the exposed surface of the vestibule, keeping it moistened. During arousal, a pair of ducts discharges the secretions of the greater vestibular glands (Bartholin's glands) into the vestibule near the posterolateral margins of the vaginal entrance. These mucous glands have the same embryological origins as the bulbourethral glands of males.

The outer limits of the vulva are established by the mons pubis and the labia majora. The bulge of the mons pubis is created by adipose tissue beneath the skin anterior to the pubic symphysis. Adipose tissue also accumulates within the labia majora (singular, labium majus), prominent folds of skin that encircle and partially conceal the labia minora and adjacent structures. The outer margins of the labia majora and the mons pubis are covered with coarse hair, but the inner surfaces of the labia majora are relatively hairless. Sebaceous glands and scattered apocrine sweat glands secrete onto the inner surface of the labia majora, moistening them and providing lubrication.

The Mammary Glands

A newborn infant cannot fend for itself, and several of its key systems have yet to complete their development. Over the initial period of adjustment to an independent existence, the infant gains nourishment from the milk secreted by the maternal mammary glands. Milk production, or lactation, occurs in these glands, which in females are specialized organs of the integumentary system that are controlled primarily by hormones of the reproductive system and the placenta, a temporary structure that provides the embryo or fetus with nutrients.

On each side, a mammary gland lies in the subcutaneous tissue of the pectoral fat pad beneath the skin of the chest (Figure 28-23). Each breast bears a small conical projection, the nipple, where the ducts of underlying mammary gland opens onto the body surface. The reddish-brown region of skin around each nipple is the areola. Large sebaceous glands beneath the areolar surface give it a grainy texture.

The glandular tissue of the mammary gland consists of separate lobes, each containing several secretory lobules. Ducts leaving the lobules converge, giving rise to a single lactiferous duct in each lobe (Figure 28-23 ). Near the nipple, that lactiferous duct enlarges, forming an expanded chamber called a lactiferous sinus. Typically, 15-20 lactiferous sinuses open onto the surface of each nipple.

Dense connective tissue surrounds the duct system and forms partitions that extend between the lobes and the lobules. These bands of connective tissue, known as the suspensory ligaments of the breast, originate in the dermis of the overlying skin. A layer of loose connective tissue separates the mammary complex from the underlying pectoralis muscles. Branches of the internal thoracic artery supply blood to each mammary gland (Figure 21-23 ).

Development of the Mammary Glands during Pregnancy

There are two types of mammary glands: inactive and active. The inactive, or resting, mammary gland is dominated by a duct system rather than by active glandular cells. The size of the mammary glands in a nonpregnant woman reflects primarily the amount of adipose tissue present, not the amount of glandular tissue. The secretory apparatus does not complete its development until pregnancy occurs. The active mammary gland is a tubuloalveolar gland, consisting of multiple glandular tubes that end in secretory alveoli. We shall discuss the hormonal mechanisms involved in the control of mammary gland function in Chapter 29.

CONCEPT CHECK QUESTIONS

1.                As the result of infections such as gonorrhea, scar tissue can block the lumen of each uterine tube. How would this blockage affect a woman's ability to conceive?

2.                What is the advantage of the normally acidic pH of the vagina?

3.                Which layer of the uterus is sloughed off during menstruation?

4.                Would blockage of a single lactiferous sinus interfere with delivery of milk to the nipple? Explain.