Organs of the Genital System and their Neurovasculature

5 Organs of the Genital System and their Neurovasculature


5.1 Overview of the Genital Tract


Classification of the genital organs


The genital organs of the male and female can be classified in various ways:


Topographically (A) as


internal genital organs (internal genitalia) or


external genital organs (external genitalia)


Functionally (B, C) as


organs for germ-cell and hormone production (gonads) or


organs of transport, incubation and copulation, plus accessory sex glands


Ontogenically (see p. 56) as


the undifferentiated gonad primordium (develops into the gonads)


two undifferentiated duct systems (develop into the male and female transport organs, the female uterus, a portion of the female copulatory organ, and one of the accessory sex glands in the male)


the urogenital sinus and its derivatives (giving rise to the external genitalia of both sexes, the accessory sex glands, and portions of the copulatory organs)


A Male and female internal and external genitalia*























 


Male


Female


Internal genitalia


Testis


Epididymis


Ductus deferens


Prostata


Seminal vesicle


Bulbourethral gland


Ovary


Uterus


Uterine tube


Vagina (upper portion)


External genitalia


Penis and urethra


Scrotum and coverings of the testis


Vagina (vestibule only)


Labia majora and minora


Mons pubis


Greater and lesser vestibular glands


Clitoris


* The female external genitalia (pudenda) are known clinically as the vulva.


B Functions of the male genital organs





























Organ


Function


Testis


Germ-cell production


Hormone production


Epididymis


Reservoir for sperm (sperm maturation)


Ductus deferens


Transport organ for sperm


Urethra


Transport organ for sperm and urinary organ


Accessory sex glands (prostate, seminal vesicles, and bulbourethral glands)


Production of secretions (semen)


Penis


Copulatory and urinary organ


C Functions of the female genital organs





























Organ


Function


Ovary


Germ-cell production


Hormone production


Uterine tube


Site of conception and transport organ for zygote


Uterus


Organ of incubation and parturition


Vagina


Organ of copulation and parturition


Labia majora and minora


Copulatory organ


Greater and lesser vestibular glands


Production of secretions



For these reasons, the collective term urogenital system is generally used.


5.2 Female Internal Genitalia: Overview



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A Projection of the female internal genitalia onto the pelvis


Anterior view. The bifurcation of the abdominal aorta into the common iliac arteries is also shown to aid orientation. The uterus, like the vagina, is located in the pelvic midline while the ovaries are superior, lateral, and posterior to the uterus in the RLQ and LLQ. Each ovary occupies a fossa located just inferior to the division of the common iliac artery. The uterine tubes do not pass to the ovaries by the shortest route but circle around them from the lateral side, because both of the paramesonephric ducts (which develop into the uterine tubes) run lateral to the gonadal ridge in which the ovaries develop.



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B Uterus and vagina: relationship to the pelvic organs


Midsagittal section through a female pelvis, viewed from the left side. The peritoneum has been outlined in color. The uterus directly overlies the bladder, and the rectum is posterior to the uterus. The fundus and corpus (body) of the uterus are covered by visceral peritoneum, which is reflected onto the bladder and rectum to form the vesicouterine pouch and rectouterine pouch. The peritoneum extends farther down the posterior wall of the uterus than its anterior wall, with the result that the posterior part of the uterine cervix and upper vagina is covered by peritoneum while the anterior part is not. The vagina is surrounded on all sides by pelvic connective tissue. This tissue is thickened anteriorly and posteriorly to form the vesicovaginal and rectovaginal septa.



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C The female genital organs in situ


Slightly angled coronal section, anterior view. The bladder, which lies anterior to the vagina and inferior to the uterine fundus (see B), is not shown. This illustration represents a compilation of multiple sections to provide a single integrated view. The uterine fundus, which is directed anteriorly owing to its anteverted and anteflexed position (see p. 326), projects out of the deeper plane of section toward the observer. Around the vagina is a connective-tissue space containing an elaborate venous plexus. This loose connective tissue allows for considerable expansion of the vagina during childbirth. The sections of arterial vessels are arterial branches to the vagina as well as sections of the inferior vesical arteries. See p. 394f for the subdivisions of the pelvic space and structure of the pelvic floor.


5.3 Female Internal Genitalia: Topographical Anatomy and Peritoneal Relationships; Shape and Structure




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B Folds of peritoneum on the female genital organs (after Graumann, von Keyserlingk, and Sasse)


Sagittal section through the broad ligament of the uterus. The ovary, uterine tube, and much of the uterus (see A) are covered by peritoneum. The uterine tube is attached to the superior margin of the broad ligament by the mesosalpinx. The ovary is attached to the posterosuperior surface of the broad ligament by its own peritoneal structure, the mesovarium. These peritoneum-covered bands of connective tissue perform the same functions for the genital organs as the mesenteries do for the bowel and are named accordingly (see C): the mesovarium for the ovary, the mesosalpinx for the uterine tube (salpinx), and the mesometrium for the uterus. Collectively they form the broad ligament.


C Ligaments and peritoneal structures of the female genital organs

























Broad ligament of uterus


Broad fold of peritoneum extending from the lateral pelvic wall to the uterus (transmits vascular structures to the internal genital organs). The ligament has three main parts that extend to specific organs:


Mesometrium = to the uterus


Mesosalpinx = to the uterine tube


Mesovarium = to the ovary


The connective-tissue space between the two peritoneal layers of the broad ligament is known clinically as the parametrium


Transverse cervical ligament (cardinal ligament)


Transverse bands of connective tissue between the uterine uterina and pelvic wall (paracervix, see p. 396)


Round ligament of uterus


Distal remnant of the gubernaculum (embryonic cord in both sexes, guides the descent of the testis or ovary). Extends from the lateral angle of the uterus through the inguinal canal into the subcutaneous connective tissue of the labium majus


Rectouterine fold


Peritoneum-covered fold of connective tissue between the uterus and rectum; often contains smooth muscle (rectouterine muscle)


Proper ovarian ligament


Proximal remnant of gubernaculum passing from the uterine pole of the ovary to the angle of the uterus with the uterine tube


Ovarian suspensory ligament


Fold of peritoneum stretching from the pelvic wall to the ovary; transmits the ovarian vessels




5.4 Female Internal Genitalia: Wall Structure and Function of the Uterus



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A Longitudinal section through the uterus


Viewed from the left side.


B Wall structure of the uterus



The uterine wall also consists of three layers from inside to outside:


Mucosa or endometrium (see D): Single layer of columnar epithelium (epithelial layer) on a connective-tissue base (lamina propria)


Muscular coat or myometrium (see C): Several smooth-muscle layers with a total thickness of approximately 1.5 cm


Serous coat or perimetrium: Serosa covering the anterior and posterior sides of the uterine corpus and the posterior wall of the uterine cervix. The subserosa adjacent to the myometrium becomes adventitia in areas where the uterus lacks a peritoneal covering (e.g., at the attachment of the uterine broad ligament). of the uterine broad ligament).



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C Layers of the myometrium (after Rauber and Kopsch)


The myometrium (tunica muscularis) of the uterus consists of three layers from outside to inside:


Supravascular layer: thin outermost layer with criss-crossing lamellae; stabilizes the uterine wall


Vascular layer: thick intermediate layer with a reticular pattern of muscle fibers; very vascular; the principal source for uterine contractions during labor


Subvascular laye: thin innermost layer just below the endometrium; provides for functional closure of the uterine ostium of the uterine tube. Its contraction promotes separation of the uterine mucosa (shedding of the functional layer) during menses and separation of the placenta after childbirth.


The myometrium performs two seemingly contradictory functions: It must keep the uterus closed during pregnancy, but it must open the cervix during childbirth. To fulfill these functions, the individual muscle layers (see above) are equipped with longitudinal, oblique, and transverse or circular fibers. The circular muscle fibers are most abundant in the cervical region and serve to maintain closure of the cervix during pregnancy. The longitudinal and oblique muscle fibers are most abundant in the uterine body and fundus; they shorten the uterus and lower the fundus during childbirth. The myometrium blends with the circular fibers of the uterine tube muscles at the uterine fundus near the tubal ostium. Myometrial contractions are stimulated most effectively by the pituitary hormone oxytocin. These contractions occur not only during labor and delivery but also during menstruation, when they aid in expulsion of the uterine mucosa. Benign tumors of the myometrium (fibroids, myomas) may cause abnormalities of menstrual bleeding.




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E Cyclical changes in the endometrium


The ovary secretes estrogens (e.g., estradiol) and progestins (e.g., progesterone) on a cyclical basis. Estrogens stimulate proliferation of the endometrium, while progestins induce its secretory transformation. The release of both hormones is controlled chiefly by the hormones FSH (follicle stimulating hormone) and LH (luteinizing hormone), which are secreted cyclically by the pituitary gland. While estrogens are produced by the ovarian follicle, progestins are produced in significant amounts only by the corpus luteum. If conception does not take place, the corpus luteum regresses and stops producing hormones. As a result of this, the functional layer of the endometrium breaks down and is expelled during menstruation. Estrogen production by a new, pituitary-stimulated ovarian follicle initiates a new cycle, which lasts an average of 28 days (1 lunar month). Ovulation usually occurs on day 14 of the cycle.


Note: For practical reasons, the first day of the menstrual period (which lasts about 4 days) is considered day 1 of the cycle, despite the fact that the cycle ends with menstruation. This is because the sudden onset of menstrual bleeding is easier to detect than its more gradual cessation. From the standpoint of the endometrium, however, the last day of the menstrual period (difficult to detect) marks the end of the cycle.


5.5 Female Internal Genitalia: Positions of the Uterus and Vagina



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A Curvature and position of the uterus


Midsagittal section of the uterus and upper vagina, viewed from the left side.


Note the two angles that determine the normal anteversion and anteflexion of the uterus (see D). Posterior angulation and curvature of the uterus (retroflexion, retroversion) are considered abnormal. A retroverted uterus is more susceptible to descent because it is more closely aligned with the longitudinal axis of the vagina. Moreover, a retroverted uterus that enlarges during pregnancy may become immobile below the sacral promontory (L 5/S1 junction) and jeopardize the further course of the pregnancy by constraining uterine expansion.



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B Position and level of the uterus in the pelvis


Coronal section of the pelvis, anterior view. The uterus has been slightly straightened for clarity. Normally the uterus is located approximately in the median plane (a) with its vaginal part level with a line connecting the two ischial spines. The uterus may be displaced from this position to the left or right (sinistroposition or dextroposition, b and c) or may lie above or below the plane of the ischial spines (elevation or descent, see d and e). Anterior and posterior displacement (anteposition, retroposition) may also occur but are not illustrated here. Descent of the uterus usually results from a structural weakness of the pelvic floor (chiefly the levator ani, often after numerous vaginal deliveries). Displacement of the uterus may cause complaints and functional disturbances due to pressure on adjacent organs (bladder, rectum). Descent of the uterus may even cause the vaginal part of the uterus to protrude from the vagina (cervical prolapse).



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C Physiological changes in uterine position


Midsagittal section of the pelvis, viewed from the left side. Uterine position is directly affected by the varying degrees of bladder and rectal distention. 1 Bladder and rectum empty; 2 bladder and rectum full; 3 bladder full, rectum empty.


D Describing the position of the uterus in the pelvis


The position of the uterus in the pelvis can be described in terms of version, flexion, and position (angles are shown in A).
















Version


Inclination of the cervix in the cavitas pelvis; defined by the angle between the cervical axis and the longitudinal axis of the body; the normal condition is anteversion


Flexion


Inclination of the corpus uteri relative to the cervix; defined by the angle between the longitudinal axes of the cervix and corpus uteri; the normal condition is anteflexion


Position


Position of the vaginal part of the uterus in the pelvic cavity; physiologically, the vaginal part of the uterus is at the level of the interspinous line at the center of the pelvis




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F Location of the vagina in the pelvic floor


This drawing illustrates the close proximity of the vagina and urethra. Muscular fibers from the deep transverse perineal encircle the vagina.



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G Location of the vagina in the pelvis


Midsagittal section through a female pelvis, viewed from the left side. The longitudinal axis of the vagina is directed posterosuperiorly. The vagina is attached to the pelvic connective tissue anteriorly (vesicovaginal septum), posteriorly (rectovaginal septum), and laterally (not shown here). The vaginal fornix surrounds the vaginal part of the cervix, which itself is directed superiorly and anteriorly. The posterior fornix is significantly longer than the anterior fornix and projects further superiorly in the pelvis. The visceral peritoneum extends far down the posterior uterine wall, bringing the posterior part of the vaginal fornix into close proximity to the rectouterine pouch (cul-de-sac, the lowest part of the female peritoneal cavity).


5.6 Female Internal Genitalia: Epithelial Regions of the Uterus



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A Epithelial regions of the uterus


a aCoronal section through uterus, anterior view; b–d Higher magnification of a: b Mucus-secreting columnar epithelium of the cervical canal; c Squamous epithelium of the vaginal part of cervix; d PAS method used to display glycogen (after Luellmann).


The cervix is the lower part of the uterus. It commences distal to the isthmus of the uterus as the supravaginal part of the cervix, which is the upper part of the cervix surrounded by connective tissue of the parametrium, and ends at its lower portion that extends into the vagina (vaginal part of cervix). At the level of the supravaginal part of the cervix the uterus is held in place by ligaments (mainly the cardinal ligament, cf. p. 388). The tubular lumen of the cervix is called the cervical canal. It is lined with mucosa and begins at the internal os and ends with the external os at the vaginal part of the cervix. The mucosal epithelium of the cervical canal is composed of a single layer of mucus-secreting columnar epithelium. A parallel arrangement of folds (palmate folds), which form crypts, gives the epithelium a rough appearance on the surface. The function of the reserve cells located at the base of the epithelium is to replenish the cervical epithelium. Unlike the one-layered cervical epithelium, the vagina is lined with stratified, nonkeratinized squamous epithelium, which depending on the hormonal situation in women may continue to the surface of the vaginal part of the cervix. The boundaries of the two epithelial layers can be either endo- or ectocervical (see C). The stratified, nonkeratinized squamous epithelium lining the vagina (and vaginal part of cervix) is composed of up to 20 layers of cells and is made up of four tiers: basal, parabasal, intermediate, and superficial layers. Typically, cells of the two superficial-most layers contain abundant glycogen as a result of differentiation. The epithelium exhibits cyclical changes: whereas at the preovulatory stage, all layers are well developed, at the postovulatory stage cells of the superficial and intermediate layers desquamate and disintegrate. Glycogen that is released as a result nourishes lactic acid bacteria (lactobacillus acidophilus, Döderlein’s bacillus), which inhabit the vagina. The transformation of glycogen into lactic acid leads to the acidic vaginal milieu (pH 4–5), which mainly in the second half of the menstrual cycle protects against pathogens (see B). The slightly alkaline cervical mucus has a similar effect as a physiologic barrier against infection. For much of the menstrual cycle, it has a stretchy texture and seals the cervical canal with a protective plug (barrier against ascending germs). The mucus is thin only at the time of ovulation and thus becomes penetrable by sperm.


B Defense mechanisms of the vagina and potential dysfunctions


The peritoneal cavity has an anatomical communication with the exterior of the body (via vagina–cervical canal–uterine cavity–uterine tube). This exposes the female to ascending infections, and this is why physiologic barriers against infection exist in the form of vaginal defense mechanisms. Dysfunction of these mechanisms may lead to gynecological inflammation and an increased risk of miscarriage.














Protection mechanism


Dysfunction due to


Physiological acidic vaginal milieu with a pH 4–5


Effect of estrogens: stimulates vaginal epithelium proliferation and differentiation (glycogen storage)


Effect of progestins: leads to desquamation of superficial and intermediate vaginal cells


Conversion of glycogen into lactic acid through lactobacillus acidophilus (Döderlein’s bacillus)


Elevated pH level: alkalizing effect of menstrual blood/cervical mucus


Lack of glycogen: lack of endogenous estrogen/progestins (childhood/old age/diseases)


Drugs: antibiotics disrupt vagina’s normal flora


Exogenous effects: sex life, tampons, improper anal hygiene, using alkaline soaps


Infections: colpitis especially caused by chlamydia, trichomonads and fungi (candida albicans)



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C Uterine cervix: Epithelial regions in pre-reproductive and post-reproductive stages


a, c, e, and g: highly schematic coronal sections of the uterus and vagina, anterior view; colposcopic images of the cervical part of the cervix before the onset of puberty (b nullipara) and during the reproductive phase (d and f multipara); b, d, and f from Nauth, H.F.: Gynäkologische Zytodiagnostik. Thieme, Stuttgart 2002).


The arrowheads mark the location of the internal os; the dashed lines mark the boundaries of the cervical canal (a). The boundary between the unilayered mucus-secreting columnar epithelium (cervical epithelium) of the cervical canal and the stratified nonkeratinized squamous epithelium of the vaginal part of the cervix and the vagina varies according to the woman’s hormonal status (see below). The visible portion of the uterus is called the ectocervix and the non-visible portion is called the endocervix.


Before the onset of puberty (a and b): Before the onset of the reproductive phase, the cervical part of the cervix is covered with squamous epithelium, the ecto-endocervical boundary is located within the cervical canal (above the external os), thus it is not visible from the vagina. During the reproductive phase (c–f): in response to hormonal stimuli (estrogen) the cervical mucosa is everted and moves inside the vagina. It appears as a glandular field with a very rough surface on the ectocervix (d). The sharp boundary with the smooth pink-colored squamous epithelium of the vaginal part of the cervix is thus located outside of the external os and is clearly visible from the vagina. The eversion of the cervical glandular field is believed to be related to higher fertility (easier for spermatozoa to enter the cervix). The columnar endocervical epithelium, which has everted onto the ectocervix adjusts to the altered vaginal milieu (acidic milieu in contrast to alkaline milieu of the cervical canal) by converting to stratified nonkeratinized squamous epithelium (metaplasia). In this way, it is similar in structure and cyclic behavior to the regular squamous epithelium of the vaginal part of the cervix. As the mucus-secreting cervical epithelium transforms into squamous epithelium the columnar glands become sealed over (closed transformation zone in contrast to open transformation zone where the glands are not overgrown and occluded, arrows in f point to the “open” orifices) leading to the formation of macroscopically visible mucus-filled retention cysts (Nabothian cysts), which are not considered problematic. Squamous epithelium in the transformation zone may become malignant and contribute in pre-stages (precancerous) to squamous cell carcinoma formation (see p. 330 f).


During postmenopause (g): lower estrogen levels toward the end of the reproductive phase cause the relocation of cervical epithelium and the boundary of the endo- and ectocervix moves back into the cervical canal (similar clinical presentation to b although the cervix changes shape after vaginal delivery).


5.7 Female Internal Genitalia: Cytologic Smear, Conization; Cervical Carcinoma



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A Cytologic smear: cell morphology of vaginal and vaginal part of cervical epithelium; early detection of cervical cancer


a and b cytologic smears taken from the vaginal part of the cervix and the cervical canal, c transfer of smear material onto glass slide; d histological structure and cell morphology of the vaginal and cervical epithelium in the cytologic smear; e Pap staining of superficial and intermediate cells (e from Nauth H.F.: Gynäkologische Zytodiagnostik. Thieme, Stuttgart 2002).


Especially in the transformation zone of the uterine cervix, where with the onset of puberty the unilayered columnar epithelium of the cervix changes into stratified squamous epithelium (see p. 329), the squamous epithelium may undergo malignant transformation and turn into invasive squamous cell carcinoma. Because cervical cancer usually develops slowly over time, it is possible to detect it in its early stages with the help of cytologic smears. Thus, cytodiagnosis is one of the most important tools in early detection of cervical cancer (see D). Cytology testing is an obligatory part of the initial gynecologic examination and cancer screening (in Germany starting at the age of 20) and is also performed to evaluate suspicious changes in cervical tissue. The cytologic smear should always include cells from the uppermost epithelial layer, which if they are normal show signs of differentiation (see p. 328).


Two smears are taken routinely: the first one (a) must be taken at the surface of the vaginal part of the cervix (ectocervix), and the second one (b) from the cervical canal (endocervix). The smear material is taken with a cotton swab and transferred to a slide and fixed (c). After that, the Papanicolaou method (known as Pap stain) is used to stain the cervical smear and evaluate it for characteristics of cell differentiation (cell shape, nuclear shape, nucleus-plasma ratio, see D). Because structure, height and the degree of maturation vary with the hormonal status (menstrual cycle) of a woman, it is crucial to confirm at which point during the cycle the smear is taken. If it is taken during the follicular phase (effect of estrogen), it is dominated by eosinophilic superficial cells, which are stained red, and flat, basophilic intermediate cells with pyknotic nuclei, which are stained greenish-blue (e). This proliferative phase, during which the uppermost cell layer is constantly regenerated by cells from the basal layer, normally lasts about a week. The postovulatory phase is dominated by cell differentiation and desquamation. Hence, the epithelium is thinner in the second part of the menstrual cycle.


Aug 4, 2021 | Posted by in GENERAL SURGERY | Comments Off on Organs of the Genital System and their Neurovasculature
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