Chapter 2: Maternal Anatomy ANTERIOR ABDOMINAL ABDOMINAL WALL Skin, Subcutaneous Layer, and Fascia Anterior Abdominal Wall Confines abdominal viscera Stretches to accommodate the expanding uterus Provides surgical access to the internal reproductive organs. Langer lines describe the orientation of dermal fibers within the skin. Anterior abdominal wall: arranged transversely. Vertical skin incisions sustain increased lateral tension thus develop wider scars. Low transverse incisions (Pfannenstiel (Pfannenstiel)) follow Langer lines and lead to superior cosmetic results. Subcutaneous Layer a) Superficial Predominantly fatty layer (Camper ( Camper Fascia) Fascia) b) Deeper membranous layer (Scarpa (Scarpa Fascia) Fascia) Camper Fascia Continues onto the perineum to provide fatty substance to the mons pubis and labia majora Blend with the fat of the ischioanal fossa. Scarpa Fascia Continues inferiorly onto the perineum as Colles fascia Perineal infection or hemorrhage superficial to Colles fascia has the ability to extend upward to involve the superficial layers of the abdominal wall. Beneath the subcutaneous layer, the anterior abdominal wall muscles consist of the following which extend across the entire wall a) Midline Rectus Abdominis b) Pyramidalis Muscles c) External Oblique d) Internal Oblique e) Transversus Abdominis Muscles Fibrous aponeuroses of these three latter muscles form the primary fascia of the anterior abdominal wall. Fuse in the midline at the Linea Alba Normally measures 10 to 15 mm wide below the umbilicus Abnormally wide separation separation may reflect Diastasis Recti or Recti or Hernia. Three aponeuroses also invest the rectus abdominis muscle as t he Rectus Sheath. Sheath. Construction of this sheath varies above and below a boundary, Arcuate Line Cephalad: aponeuroses invest the rectus abdominis bellies on both dorsal and ventral surfaces. Caudal: all aponeuroses lie ventral or superficial to the rectus abdominis muscle Only the thin transversalis fascia and peritoneum lie beneath the rectus Transition of rectus sheath composition can be seen best with a midline abdominal incision Pyramidalis Muscles Paired small triangular muscles O: pubic crest, I: linea alba Lie atop the rectus abdominis muscle but beneath the anterior rectus sheath. Blood Supply Arise from the the Femoral Artery just Artery just below the inguinal ligament within the femoral triangle a) Superficial Epigastric b) Superficial Circumflex Iliac c) Superficial External Pudendal Supply the skin and subcutaneous layers of the anterior ab dominal wall and mons pubis. Superficial Epigastric vessels Epigastric vessels course diagonally toward the umbilicus. With a low transverse skin incision, can usually be identified at a depth halfway between the skin and the anterior rectus sheath, above S carpa fascia, and several centimeters from the midline. Branches of the External Iliac Vessels a) Inferior “Deep” Epigastric b) Deep Circumflex Iliac Supply the muscles and fascia of the anterior abdominal wall Inferior Epigastric vessels Epigastric vessels initially course lateral to, then posterior to the rectus abdominis muscles, which they supply. Pass ventral to the posterior rectus sheath and course between the sheath and the rectus muscles. Near the umbilicus, anastomose with the Superior Epigastric Artery and Veins, which are branches of the Internal Thoracic Vessels. Maylard incision: Inferior Epigastric Artery may Artery may be lacerated lateral to the rectus belly during muscle transection. These vessels rarely may rupture following abdominal trauma and create a rectus Sheath Hematoma Hesselbach Triangle Lie on each side of the lower anterior abdominal wall Bounded: L-inferior epigastric vessels, I: inguinal ligament, M: lateral border of the rectus muscle. Direct Inguinal Hernias: Hernias : hernias that protrude through the abdominal wall in Hesselbach triangle. Indirect Inguinal Hernias: hernias that protrude through deep inguinal ring, which lies lateral to this triangle, and then may exit out the superficial inguinal ring.
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Innervation Anterior Abdominal Abdominal Wall is innervated by a) Intercostal Nerves (T7 Nerves (T7 –11) –11) b) Subcostal Nerve (T12), Nerve (T12), c) Iliohypogastric and Ilioinguinal Nerves (L1) Nerves (L1) Intercostal and Subcostal Nerves are Nerves are Anterior Rami of the Thoracic Spinal Nerves Run lateral and then anterior abdominal wall between the transversus abdominis and internal oblique muscles(Transversus muscles( Transversus Abdominis Plane) Plane ) Near the rectus abdominis lateral borders, these nerve bran ches pierce the posterior sheath, rectus muscle, and then anterior sheath to reach the skin. May be severed during a Pfannenstiel incision at the point in wh ich the overlying anterior rectus sheath is separated from the rectus muscle. Iliohypogastric and Iliohypogastric and Ilioinguinal Nerves originate Nerves originate from the Anterior Ramus of the First Lumbar Spinal Nerve Emerge lateral to the psoas muscle and travel across the quadratus lumborum inferomedially toward the iliac crest. Near this crest, both nerves pierce the transversus abdominis muscle and course ventrally. 2 to 3 cm medial to the anterior superior iliac spine, they pierce the internal oblique muscle and course superficial to it toward the m idline Iliohypogastric Iliohypogastric Nerv e Perforates the external oblique aponeurosis near the lateral rectus bor der to provide sensation to the skin over t he suprapubic area. Ilioinguinal Ilioinguinal Nerve Course medially through the inguinal canal and exits through the Superficial Inguinal Ring, Ring , which forms by splitting of external abdominal oblique aponeurosis fibers. Supplies the skin of the mons pubis, upper labia majora, and medial u pper thigh. Ilioinguinal and Iliohypogastric Nerves can Nerves can be severed during a low transverse incision or entrapped during closure, especially if incisions extend beyond the lateral borders of the rectus muscle These nerves carry sensory information only and injury leads to loss of sensation within the areas supplied. Rarely, chronic pain may develop. T10 dermatome approximates dermatome approximates the level of the umbilicus. Regional analgesia for cesarean delivery or for puerperal sterilization ideally blocks T10 through L1 levels. Transversus Abdominis Plane Block can Block can provide broad blockade to the nerves that traverse this plane May be placed post cesarean to reduce analgesia requirements Rectus Sheath Block or Block or Ilioinguinal-Iliohypogastric Ilioinguinal-Iliohypogastric Nerve Block to Block to decrease postoperative pain
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EXTERNAL GENERATIVE ORGANS Vulva Mons Pubis, Labia, and Clitoris Pudenda Commonly designated the vulva Includes all structures visible externally from the symphysis pubis to the perineal body. Includes: Mons Pubis, Labia Majora an d Minora, Clitoris, Hymen, Vestibule, Urethral Opening, Greater Vestibular (Bartholin Glands), Minor Vestibular Glands and Paraurethral Glands
Mons Pubis Also called the Mons Veneris Fat-filled cushion overlying the symphysis pubis. After puberty, it is covered by curly hair that forms the escutcheon. In In women, hair is distributed in a triangle, whose base c overs the upper margin of the symphysis pubis In men and some hirsute women, the escutcheon is not so well circumscribed and extends onto the anterior abdominal wall toward the umbilicus. Labia Majora Homologous with the male scrotum. 7-8 cm in length, 2-3 cm in depth, and 1-1.5 cm in thickness S: continuous directly with the mons pubis and round ligaments terminate at their upper borders. P: taper and merge into the area overlying the perineal body to form the Posterior Commissure. Hair covers the labia majora outer surface b ut is absent on their inner surface. Apocrine, eccrine, and sebaceous sebaceous glands are abundant. Beneath the skin is a dense connective tissue layer, which is nearly void of muscular elements but is rich in elastic fibers and adipose tissue. Mass of fat provides bulk to the labia majora Supplied with a rich venous plexus During pregnancy: vasculature commonly develops varicosities, especially in parous women Due to increased venous pressure created by the enlarging uterus. Appear as engorged tortuous tortuous veins or as small grapelike clusters clusters but typically asymptomatic. Each is a thin tissue fold that lies medial to each labium majus Males: homologue forms the ventral shaft of the penis. Labia Minora Extends superiorly where each divides into two lamellae From each side, lower lamellae fuse to form the frenulum of the clitoris Upper merge to form the prepuce Inferiorly extend to approach the midline as low ridges of tissue that join to form the fourchette Lengths: 2 -10 cm, widths 1-5 cm Composed of connective tissue with numerous vessels, elastin fibers, and very few smooth muscle fibers Supplied with many nerve endings and extremely sensitive. Thinly keratinized stratified squamous epithelium covers the outer surface of each labium. Inner surface: lateral portion is covered by this same epithelium up to a demarcating line (Hart ( Hart Line) Line) Medial: each labium is covered by nonkeratinized squamous epithelium Lack hair follicles, eccrine glands, and apocrine glands but many sebaceous glands Clitoris Principal female erogenous organ Erectile homologue of the penis. Located beneath the prepuce, above the frenulum and urethra, projects downward and inward toward the vaginal opening Rarely exceeds 2 cm in length Composed of a) Glans b) Corpus or body c) Two crura Glans Usually < 0.5 cm in diameter Covered by stratified squamous epithelium Richly innervated
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Clitoral Body Contains two corpora cavernosa Extending from the clitoral body, each corpus cavernosum diverges laterally to form long narrow crus. Each crus lies along the inferior surface of its respective ischiopubic ramus, deep to the ischiocavernosus muscle. Blood supply stems from branches of the Internal Pudendal Artery Deep Artery of Artery of the clitoris supplies the clitoral body Dorsal Artery of Artery of the clitoris supplies the glans and prepuce.
Vestibule Functionally mature female structure derived from the embryonic urogenital membrane An almond-shaped area Enclosed by L: Hart line, M: external surface of the hymen, A: clitoral frenulum, P: fourchette Perforated by six openings: a) Urethra b) Vagina c) two Bartholin gland ducts d) two ducts of the largest Paraurethral Glands (Skene glands) Fossa Navicularis Posterior portion of the vestibule between the fourchette and the vaginal opening Usually observed only in nulliparas. bilateral Bartholin Glands Also termed Greater Vestibular Glands 0.5 -1 cm in diameter Each lies inferior to the vascular vestibular bulb and deep to the inferior end of the bulbocavernosus muscle Duct from each measures 1.5 - 2 c m long Opens distal to the hymeneal ring One at 5 and the other at 7 o’clock on the vestibule. Following trauma or infection, either duct may swell and obstruct to form a cyst or, if infected, an abscess. Minor Vestibular Glands Shallow glands lined by s imple mucin-secreting epithelium Open along Hart line Paraurethral Glands Collective arborization of glands whose multiple small ducts open predominantly along the entire inferior aspect of the urethra. Two Largest are called Skene Glands Ducts typically lie distally and near the urethral meatus. Inflammation and duct obstruction of any of the paraurethral glands can lead to urethral diverticulum formation. Lower two thirds of the urethra lie immediately above the anterior vagi nal wall Urethral opening or meatus is in the midline of the v estibule 1-1.5 cm below the pubic arch and short distance above the vaginal opening.
Vagina and Hymen Hymen Membrane of varying thickness that surrounds the vaginal opening more or less completely. Composed mainly of elastic and collagenous connective tissue Both outer and inner surfaces are covered by non-keratinized stratified squamous epithelium Aperture of the intact hymen ranges in diameter diameter from pinpoint to one that admits one or even two fingertips. Imperforate Hymen Rare malformation in which the vaginal orifice is occluded completely causing retention of menstrual blood As a rule, the hymen hymen is torn at several sites sites during first coitus. Edges of the torn tissue soon reepithelialize Pregnant women: hymeneal epithelium is thick and rich in glycogen. Over time, the hymen transforms into several nodules of various s izes, termed Hymeneal or Hymeneal or Myrtiform Caruncles. Caruncles. Vagina Proximal to the hymen Musculomembranous tube that extends to the uterus Interposed lengthwise between the bladder and the rectum
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Anteriorly, separated from the bladder and urethra urethra by connective tissue (Vesicovaginal Septum) Septum ) Posteriorly, between the lower portion of the vagina and the rectum together form the Rectovaginal Septum. Septum. upper fourth is separated from the rectum by the Rectouterine Pouch Also called the Cul-De-Sac or Pouch of D ouglas. Anterior wall measures measures 6-8 cm Posterior vaginal wall is 7-10 cm Upper end of the vaginal vault is subdivided by the cervix into a) Anterior b) Posterior c) two Lateral Fornices Clinical importance because the internal pelvic organs usually can be palpated through the thin walls of these fornices. Posterior fornix provides surgical access to the peritoneal cavity. Midportion of the vagina: lateral walls are attached to the pelvis by visceral connective tissue. Lateral attachments blend into investing fascia of the levator ani. Create the anterior and posterior lateral vaginal sulci. Run the length of the vaginal sidewalls and give th e vagina an H shape when viewed in cross section. Lining is composed of non-keratinized stratified squamous epithelium and underlying lamina propria. Premenopausal women: lining is thrown into numerous thin transverse ridges, known as Rugae Line the anterior and posterior vaginal walls along their length. Deep to this is a muscular layer, which contains smooth muscle, collagen, and elastin. Beneath lies an adventitial layer consisting of collagen and elastin No vaginal glands Lubricated by a transudate that originates from the vaginal subepithelial capillary plexus and crosses the permeable epithelium Due to increased vascularity during pregnancy, vaginal secretions are notably increased. After birth-related birth-related epithelial trauma and healing, fragments of stratified stratified epithelium occasionally are embedded beneath the vaginal surface. Buried epithelium continues to shed degenerated cells and keratin. Result a firm epidermal inclusion cysts, which are filled with keratin debris, may form and are a common Vaginal Cyst. Cyst. Proximal portion is supplied by the Cervical Branch of Uterine Artery and Vaginal Artery May variably arise from the Uterine or Uterine or Inferior Vesical or Vesical or directly from the Internal Iliac Artery. Artery . Middle Rectal Artery supply Artery supply the posterior vaginal wall Internal Pudendal Artery supplies Artery supplies distal walls Blood supply from each side forms anastomoses on the anterior and posterior vaginal walls with contralateral corresponding vessels. Extensive venous plexus immediately surrounds the vagina and follows the course of the arteries. Lymphatics from the lower third, along with those of the vulva, dr ain primarily into the Inguinal Lymph Nodes. Nodes. Middle third drain into the Internal Iliac Nodes Upper third drain into the External, Internal, Internal, and Common Iliac Nodes. Nodes.
Perineum Diamond-shaped area between the thighs has boundaries that mirror those of the bony pelvic outlet: A: pubic symphysis, AL: ischiopubic rami and ischial ischial tuberosities, PL:sacrotuberous ligaments, P:coccyx tuberosities divides the perineum into an an An arbitrary line joining the ischial tuberosities anterior triangle (urogenital triangle) and posterior triangle (anal triangle) Perineal Body Fibromuscular mass found in the midline at the junction between these anterior and posterior triangles Also called the Central Tendon of the Perineum Measures 2 cm tall and wide and 1.5 cm thick Serves as the junction for several structures and provides significant perineal support Superficially, the bulbocavernosus, superficial transverse perineal, and external anal sphincter muscles converge on the c entral tendon. More deeply, perineal membrane, portions of the pubococcygeus muscle, and internal anal sphincter contribute Rem
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Incised by an episiotomy incision and is torn w ith second-, third-, and fourth-degree lacerations.
Superficial Space of the Anterior Triangle Bounded by: S:pubic rami, L:ischial tuberosities, P: superficial transverse perineal muscles Divided into superficial and deep spaces by the Perineal Membrane. Membranous partition is a dense fibrous sheet that was previously known as the Inferior Fascia of the Urogenital Diaphragm. Attaches: L:ischiopubic rami, M: distal third of the urethra and vagina, P: perineal body, A:arcuate ligament of the pubis. Superficial space of the anterior triangle is bounded deeply by the Perineal Membrane and Membrane and superficially by Colles Fascia. Fascia. Colles fascia is fascia is the continuation of Scarpa fascia onto the perineum. On the perineum, Colles fascia securely attaches L: pubic rami and fascia lata of the thigh, I: superficial transverse perineal muscle and inferior border of the perineal membrane, M: urethra, clitoris, and vagina. Superficial space of the anterior triangle is a relatively closed compartment, and expanding infection or hematoma within it may bulge yet remains contained. Superficial pouch contains several i mportant structures: Bartholin glands, vestibular bulbs, clitoral body and crura, branches of the pudendal vessels and nerve, and ischiocavernosus, bulbocavernosus, and superficial transverse perineal muscles. Ischiocavernosus muscles each attach on their respective side: I: medial aspect of the ischial tuberosity L: ischiopubic ramus A: clitoral crus Help maintain clitoral erection by compressing the crus to obs truct venous drainage. Bilateral bulbocavernosus muscles Overlie the vestibular bulbs and Bartholin glands. A: body of the the clitoris (A) and the perineal perineal body (P). Constrict the vaginal lumen and aid release of secretions fr om the Bartholin glands. Contribute to clitoral erection by compressing the deep dorsal vein of the clitoris. Bulbocavernosus and ischiocavernosus muscles also pull the c litoris downward. Superficial transverse perineal muscles are narrow strips that attach to the ischial tuberosities (L) and the perineal body (M) May be attenuated or even absent, but when present, they contribute to the perineal body Vestibular Bulbs Embryologically correspond to the corpora spongiosa of the penis Almond-shaped aggregations of veins 3-4 cm long, 1-2 cm wide, and 0.5-1 cm thick Lie beneath the bulbocavernosus muscle on either side of the vestibule. Terminate inferiorly at the middle of the vaginal opening Extend upward toward the clitoris. Anterior extensions merge merge in the midline, below below the clitoral body. During childbirth, veins may be lacerated or even ru pture to create a vulvar hematoma enclosed within the superficial space of the anterior triangle.
Deep Space of the Anterior Triangle Space lies deep to the perineal membrane and extends up into the pelvis Continuous superiorly with the pelvic cavity Contains a) Portions of urethra and vagina b) Certain portions of internal pudendal artery branches, c) Compressor urethrae d) Urethrovaginal sphincter muscles Comprise part of the striated urogenital sphincter complex. Pelvic Diaphragm Found deep to the anterior and posterior triangles Broad muscular sling provides substantial support to the pelvic viscera. Composed of a) Levator ani b) Coccygeus muscle. c) Levator ani Composed of 1) Pubococcygeus
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2) Puborectalis 3) Iliococcygeus Pubococcygeus Pubococcygeus Muscle Also termed the Pubovisceral Muscle Subdivided based on points of insertion and function Include 1) Pubovaginalis 2) Puboperinealis 3) Puboanalis Insert into the vaginal, perineal body, and anus, respectively Vaginal birth conveys significant risk for damage to the levator ani or to its innervation Pubovisceral Muscle is more commonly damaged Injuries may predispose women to greater risk of pelvic organ prolapse or urinary incontinence Efforts are aimed at minimizing these injuries.
Posterior Triangle contains a) Ischioanal Fossae b) Anal Canal c) Anal Sphincter Sphincter Complex Anal Sphincter Complex Consists of a) Internal anal sphincter b) External anal sphincter c) Puborectalis muscle d) Branches of the pudendal nerve and internal pudendal vessels Ischioanal Fossae Also known as Ischiorectal Fossae two fat-filled wedge-shaped spaces found on either side of the anal canal comprise the bulk of the posterior triangle Each fossa has skin as its superficial base Deep apex is formed by the junction of the levator ani and obturator internus muscle. Other borders include: Obturator internus muscle fascia and ischial tuberosity (L) Anal canal and sphincter sphincter complex (IM) Inferior fascia of the downwardly sloping levator ani (SM) Maximus muscle and sacrotuberous ligament (P) Inferior border of the anterior triangle (A). Fat found within each fossa provides support to surrounding organs yet allows rectal distention during defecation and vaginal stretching during delivery. Injury to vessels in the posterior triangle can lead t o hematoma formation in the ischioanal fossa Potential for large accumulation in these easily distensible spaces. Two fossae communicate dorsally, behind the anal canal Episiotomy infection or hematoma may extend from one fossa into the other.
Anal Canal Distal continuation of the rectum Begins at the level of levator ani attachment to the rectum and e nds at the anal skin. 4-5 cm length Mucosa consists of a) Columnar epithelium (uppermost portion) b) Simple stratified squamous epithelium (begins at dentate or pectinate line continues to the anal verge) Keratin and skin adnexa join the squamous epithelium. Has several lateral tissue layers Inner layers include a) Anal Mucosa b) Internal Anal Sphincter c) Intersphincteric Space Contains continuation continuation of the rectum’s longitudinal smooth muscle layer. Outer layer contains a) Puborectalis Muscle (S) b) External Anal Sphincter (I) Within the anal canal, three highly vascularized submucosal arteriovenous plexuses (anal cushions) Aid complete closure closure of the canal and fecal continence continence when apposed.
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Increasing uterine size, excessive straining, and hard stool create increased pressure that ultimately leads to degeneration and subsequent laxity of the cushion’s supportive connective connective tissue base. These protrude into and downward through the anal canal Leads to venous engorgement within the cushions (Hemorrhoids ( Hemorrhoids)) Venous stasis results in inflammation, erosion of the cushion’s epithelium, cushion’s epithelium, and then bleeding. External Hemorrhoids Those that arise distal to the pectinate line. Covered by stratified squamous epithelium Receive sensory innervation from the Inferior Rectal Nerve. Pain and a palpable mass are typical complaints. Following resolution, a hemorrhoidal tag may remain composed of redundant anal skin and fibrotic tissue. Internal Hemorrhoids Those that form above the dentate line Covered by insensitive anorectal mucosa May prolapse or bleed but rarely become painful unless they undergo thrombosis or necrosis.
Anal Sphincter Sphincter Complex Two sphincters surround the anal canal to provide fecal continence a) External Sphincter b) Internal Anal Sphincters Both lie proximate to the vagina One or both may be torn during v aginal delivery Internal Anal Sphincter (IAS) (IAS) Distal continuation of the rectal circular smooth muscle layer. Receives predominantly parasympathetic fibers, which pass through the pelvic splanchnic nerves. Supplied by the Superior, Middle, and Middle, and Inferior Rectal Arteries Contributes the bulk of anal canal resting pressure for fecal continence and relaxes prior to defecation Measures 3- 4 cm in length At its distal margin, it overlaps the external external sphincter for 1-2 cm Distal site at which this overlap ends ( Intersphincteric Groove) Groove) Palpable on digital examination. External Anal Sphincter (EAS) (EAS) Striated muscle ring Anteriorly attaches to to the perineal body Posteriorly connects to the coccyx (anococcygeal ligament) Maintains a constant resting contraction to aid continence Provides additional squeeze pressure when continence is threatened, yet relaxes for defecation. Three parts include a) Subcutaneous b) Superficial c) Deep Portions Deep portion is composed fully or in part b y the puborectalis muscle Receives blood supply from the inferior rectal artery Branch of the internal pudendal artery Somatic motor fibers from the Inferior Rectal Branch of Branch of the Pudendal Nerve supply Nerve supply innervation. IAS and EAS may be involved in fourth-degree laceration during vaginal delivery Reunion of these rings is integral to defect repair
Pudendal Nerve Formed from the anterior rami of S2 – S2 –44 spinal nerves Courses between the piriformis and coccygeus muscles Exits through the greater sciatic foramen Posterior to the sacrospinous ligament Medial to the ischial spine When injecting local anesthetic for a pudendal nerve block, the ischial spine serves an identifiable landmark Runs beneath the sacrospinous ligament and above the sacrotuberous ligament Reenters the lesser sciatic foramen to course along the obturator internus muscle. Lies within the pudendal canal (Alcock ( Alcock canal) canal) Formed by splitting of the obturator internus investing fascia Relatively fixed as it courses behind the sacrosp inous ligament and within the pudendal canal May be at risk of stretch injury dur ing downward displacement of the pelvic floor during childbirth
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Leaves this canal to enter the perineum Divides into three terminal branches 1) Dorsal Nerve of the C litoris Runs between the ischiocavernosus muscle and perineal membrane Supply the clitoral glans 2) Perineal Nerve Runs superficial to the perineal membrane Divides into Posterior Labial Branches and Branches and Muscular Branches Serve the labial skin and the anterior perineal triangle muscles, respectively. 3) Inferior Rectal Branch Runs through the ischioanal fossa Supply the external anal sphincter, the anal mucosa, and the perianal skin Major blood supply to the perineum is via the Internal Pudendal Artery Branches mirror the divisions of the pudendal nerve.
INTERNAL GENERATIVE ORGANS
Pregnancy stimulates remarkable uterine growth due to muscle fiber hypertrophy Uterine fundus, previously flattened convexity between t ubal insertions, now becomes dome shaped. Round ligaments appear to insert at the junction of the middle and upper thirds of the organ. Fallopian tubes elongate, but the ovaries grossly appear unchanged.
Cervix Fusiform and open at each end by small apertures a) Internal Cervical Ora b) External Cervical Ora Proximally, the upper boundary of the cervix is the internal os, corresponds to the level at which the peritoneum is reflected up onto the bladder Portio Supravaginalis Supravaginalis Upper cervical segment Lies above above the vagina’s attachment to t o the cervix Covered by peritoneum on its posterior surface Cardinal ligaments attach laterally Separated from the overlying bladder by loose connective tissue. Lower cervical portion protrudes into the vagina as the Portio Vaginalis. Vaginalis . Before childbirth, the external cervical os is a small, regular, oval opening. After labor, especially especially vaginal childbirth, the orifice is converted into a transverse slit that is divided such that there are the so-called Anterior and Posterior Cervical Lips. Lips . If torn deeply during labor or delivery, the cerv ix may heal in such a manner that it appears irregular, nodular, or stellate. Ectocervix Portion of the cervix exterior to the external os Lined by nonkeratinized stratified squamous epithelium Endocervical Endocervical Canal Covered by a single layer of mucin-secreting columnar epithelium, creates deep cleftlike infoldings or “glands.” Commonly during pregnancy, the endocervical epithelium moves out and onto the ectocervix in a physiological process (Eversion) (Eversion) Stroma is composed mainly of collagen, elastin, and proteoglycans, but very little smooth muscle. Changes in the amount, composition, and orientation of these components lead to cervical ripening prior to labor onset. In early pregnancy, increased vascularity within the cervix s troma beneath the epithelium creates an ectocervical blue tint (Chadwick (Chadwick Sign). Sign ). Cervical edema leads to softening (Goodell (Goodell Sign), Sign), isthmic softening (Hegar ( Hegar Sign) Sign) Myometrium and Endometrium Most of the uterus is composed of Myometrium Smooth muscle bundles united by connective tissue containing many elastic fibers. Interlacing myometrial fibers surround myometrial vessels and contract to compress these. Integral to hemostasis at the placental site during the third stage of labor. Number of myometrial muscle fibers varies by location Levels progressively diminish caudally such that, in the cervix, muscle makes up only 10% of the tissue mass Uterine body inner wall: more muscle than in outer layers Anterior and posterior walls: ls: more muscle than in in the lateral walls. During pregnancy, the upper myometrium undergoes marked hypertrophy, but there is no significant change in cervical muscle c ontent. Uterine cavity is lined with Endometrium Composed of an overlying epithelium, invaginating glands, and supportive, vascular stroma Varies greatly throughout the menstrual cycle and during pregnancy. Divided into a) Functionalis Functionalis L ayer Sloughed with menses b) Basalis Layer Serves to regenerate the functionalis layer following each menses.
Uterus Nonpregnant uterus: situated in the pelvic cavity Between the bladder (A) and rectum (P) Entire posterior wall of the uterus is covered by s erosa (Visceral (Visceral Peritoneum) Peritoneum) Lower portion of this peritoneum forms the anterior boundary of the Rectouterine Cul-De-Sac ( Cul-De-Sac (Pouch Pouch Of Douglas) Douglas ) Only the upper portion of the anterior wall of the uterus is so covered. Peritoneum in this area reflects forward onto the bladder dome to create the Vesicouterine Pouch Lower portion of the anterior uterine wall is united to the posterior wall of the bladder by well-defined loose connective tissue layer (Vesicouterine (Vesicouterine Space) Space) During cesarean delivery, peritoneum of the vesicouterine pouch is sharply incised, and the vesicouterine space is entered. Dissection caudally within this space lifts the bladder off the lower uterine segment for hysterotomy and delivery Pear shaped Consists of two major but unequal parts. a) Body or Corpus upper triangular portion b) Cervix Lower, cylindrical portion Projects into the vagina c) Isthmus Union site of these two Special obstetrical significance because it forms the lower uterine segment during pregnancy. At each superolateral margin of the body is a Uterine Cornu From which a fallopian tube emerges This area is the origins of the r ound and uteroovarian ligaments. Between the points of fallopian tube insertion is the convex upper uterine segment (fundus) Bulk of the uterine body is muscle Inner surfaces of the anterior and posterior walls l ie almost in contact Cavity between these walls forms a mere slit Nulligravid uterus: 6-8 cm in length Multiparous uterus: 9-10 cm Averages 60 g and typically typically weighs more in parous women Nulligravidas: fundus and cervix are approximately equal in length Multiparas: cervix is only a little more than a third of the total length. Rem
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Ligaments Several ligaments that extend from the uterine surface toward the pelvic sidewalls Include a) Round Ligaments b) Broad Ligaments c) Cardinal Ligaments d) Uterosacral Ligaments Round Ligament Corresponds embryologically to the male gubernaculum testis Originates below and anterior to the origin of the fallopian tubes. Orientation can aid in fallopian tube identification during puerperal sterilization Important if pelvic adhesions limit tubal mobility and thus limit fimbria visualization prior to tubal ligation. Each extends laterally and downward into the inguinal canal, through which it passes, to terminate in the upper portion of t he labium majus.
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Sampson Artery Branch of the uterine artery Runs within this ligament Nonpregnant women: 3-5 mm in diameter Composed of smooth muscle bundles separated by fibrous tissue septa During pregnancy, these ligaments undergo considerable hypertrophy and increase appreciably in both length and diameter.
Broad Ligaments Two wing like structures that extend from the lateral uterine margins to the pelvic sidewalls. With vertical sectioning through this ligament proximate to the uterus Triangular shape can be seen Uterine vessels and ureter are found at its base Divide the pelvic cavity into anterior and posterior c ompartments. Each consists of a fold of peritoneum (Anterior ( Anterior and Posterior Leaves) Leaves ) This peritoneum drapes over structures extending from each cornu. Peritoneum a) Mesosalpinx: Overlies the fallopian tube b) Mesoteres : Around : Around the round ligament is the c) Mesovarium: Over the uteroovarian ligament Infundibulopelvic Infundibulopelvic Ligament or Ligament or Suspensory Ligament Ligament of the Ovary Peritoneum that extends beneath the fimbriated end o f the fallopian tube toward the pelvic wall forms the. Contains nerves and the ovarian vessels During pregnancy, these vessels, especially the venous plexuses, are dramatically enlarged. Diameter of the ovarian vascular pedicle increases from 0.9 cm to reach 2.6 cm at term Cardinal Ligament Also called the Transverse Cervical Ligament or Ligament or Mackenrodt Ligament Thick base of the broad ligament Medially united firmly to the uterus and upper vagina Each uterosacral ligament originates with a posterolateral attachment to the supravaginal portion of the cervix Inserts into the fascia over the sacrum Ligaments are composed of connective tissue, small bundles of vessels and nerves, and some smooth muscle. Covered by peritoneum, these ligaments form the lateral boundaries of the pouch of Douglas. Parametrium Describe the connective tissues adjacent and lateral to the uterus within the broad ligament. Paracervical tissues are those adjacent to the cervix Paracolpium Tissue lateral to the vaginal walls.
Enters the base of the broad ligament and makes its way medially to the side of the uterus. 2 cm lateral to the cervix, the uterine artery crosses over the ureter. This proximity is of great surgical significance as the ureter may be injured or ligated during hysterectomy when the vessels are clamped and ligated. Once the uterine artery has reached the s upravaginal portion of the cervix, it divides Cervicovaginal Artery Supplies blood to the lower cervix and upper va gina Main branch turns abruptly upward and extends as a highly convoluted vessel that traverses along the lateral margin of the uterus Extends into the upper portion of the cervix, Numerous other branches penetrate the body of the uterus to form the Arcuate the Arcuate Arteries Encircle the organ by coursing within the myometrium just beneath the serosal surface. These vessels from each side anastomose at the uterine midline. From the arcuate arteries, Radial Branches originate Branches originate at right angles, traverse inward through the myometrium, enter the endometrium, and branch there to become Basal Arteries or Arteries or coiled Spiral Arteries. Arteries. Spiral Arteries Supply the functionalis layer. Vessels respond by vasoconstriction and dilatation to a number of hormones serve an important role in menstruation Basal Arteries Also called Straight Arteries Extend only into the basalis layer Not responsive to hormonal influences. Just before the main uterine artery vessel reaches the fallopian tube, it divides into three terminal branches Ovarian Branch of Branch of the uterine artery Forms an anastomosis with the terminal branch of the Ovarian Artery Tubal branch Makes its way through the mesosalpinx Supplies part of the fallopian tube Fundal branch penetrates the uppermost uterus Ovarian Artery Direct branch of the aorta Enters the broad ligament through t he infundibulopelvic ligament. Ovarian hilum: divides into smaller branches that enter the ovary. As the ovarian artery artery runs along the hilum, it also sends several branches through the mesosalpinx to supply the fallopian tubes. Main stem traverses the entire length of the broad ligament and makes its way to the uterine cornu. Forms an anastomosis with the ovarian branch of the uterine artery. Dual uterine blood supply creates a vascular reserve to prevent uterine ischemia if ligation of the uterine or internal iliac artery is p erformed to control postpartum hemorrhage. Uterine veins accompany veins accompany their respective arteries. Arcuate Veins unite Veins unite to form the Uterine Vein Empties into the internal iliac vein and then the Common Iliac Vein. Vein . Within the broad ligament, these veins form the large pampiniform plexus that terminates in the Ovarian V ein. Right Ovarian Vein empties into the Vena Cava Left Ovarian Vein empties into the Left Renal Vein. Vein. Blood supply to the pelvis is predominantly supplied from branches of the Internal Iliac Artery. Artery . Organized into anterior and posterior divisions Anterior Division Provides blood supply to the pelvic organs and perineum Includes the inferior gluteal, internal pudendal, middle re ctal, vaginal, uterine, obturator arteries and umbilical artery Continuation as the superior Vesical Artery
Blood Supply During pregnancy, there is marked hypertrophy of the uterine vasculature Supplied principally from the Uterine and Uterine and Ovarian Arteries Uterine Artery main branch of the Internal Iliac Artery previously called the Hypogastric Artery Rem
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Posterior Division Extend to the buttock and t high Include the superior gluteal, lateral sacral, and iliolumbar arteries. during internal iliac artery ligation Many advocate ligation distal to the posterior division to avoid compromised blood flow to the areas supplied by this division
Lymphatics Endometrium is abundantly supplied with lymphatic vessels that are confined largely to the basalis layer. Lymphatics of the underlying myometrium are increased in number toward the serosal surface and form an abundant lymphatic plexus just b eneath it. Lymphatics from the cervix terminate mainly in the internal iliac nodes Situated near the bifurcation of the common iliac vessels Lymphatics from the uterine corpus are distributed to two groups of n odes. Vessels drains into the Internal Iliac Nodes After joining certain certain lymphatics from the the ovarian region, terminates in the Paraaortic Lymph Nodes. Nodes . Maternal Anatomy
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Innervation Peripheral nervous system is divided a) Somatic Division Innervates skeletal muscle b) Autonomic Division Innervates smooth muscle, cardiac muscle, and glands. Pelvic visceral innervation is predominantly autonomic Further divided in Sympathetic and Sympathetic and Parasympathetic Components. Sympathetic Innervation to Innervation to pelvic viscera begins with the Superior Hypogastric Plexus (Presacral Nerve) Nerve) Beginning below the aortic bifurcation and extending downward retroperitoneally, this plexus is formed by sympathetic fibers arising from spinal levels T10-L2. At the level of the sacral promontory, divides into into a Right and a Left Hypogastric Nerve, Nerve, which run downward along the p elvis side walls
On its surface, there is a single layer of cuboidal epithelium, (Germinal (Germinal Epithelium of Waldeyer ) Beneath this epithelium, the cortex contains oocytes and developing follicles. Medulla Central portion Composed of loose connective tissue. There are a large number of arteries a nd veins and small number of smooth muscle fibers. Supplied with both sympathetic and parasympathetic nerves. Sympathetic nerves: Ovarian Plexus that Plexus that accompanies the ovarian vessels Originates in the renal plexus. Others are derived from the plexus that surrounds the ovarian branch of the uterine artery. Parasympathetic input: Vagus Nerve Sensory afferents follow the ovarian artery and enter at T10 spinal cord level.
Parasympathetic Innervation Derives from neurons at spinal levels S2-S4 Axons exit as part of of the anterior rami of the spinal nerves for those levels. levels. These combine on each side to form the pelvic splanchnic nerves (Nervi Erigentes) Erigentes) Blending of the two Hypogastric Nerves (sympathetic) Nerves (sympathetic) and the two Pelvic Splanchnic Splanchnic Nerves (parasympathetic) gives rise to the Inferior Hypogastric Plexus ( Plexus (Pelvic Pelvic Plexus) Retroperitoneal plaque of nerves lies at the S4-S5 level From here, fibers of this plexus accompany internal iliac artery bran ches to their respective pelvic viscera. Inferior Hypogastric Plexus Divides into three plexuses a) Vesical Plexus Innervates the bladder and the middle rectal travels to the rectum b) Uterovaginal Plexus (Frankenhäuser Plexus) Plexus ) Reaches the proximal fallopian tubes, uterus, and upper vagina. Extensions of the inferior hypogastric plexus also reach the p erineum along the vagina and urethra to innervate the clitoris and vestibular bulbs Composed of variably sized ganglia, but particularly of a large ganglionic plate that is situated on either side of the cervix, proximate to the uterosacral and cardinal ligaments Most afferent sensory fibers from the uterus ascend through the inferior hypogastric plexus and enter the spinal cord v ia T10-T12 and L1 spinal nerves Transmit the painful stimuli of contractions to the central nervous system Sensory nerves from the cervix and upper p art of the birth canal pass through the pelvic splanchnic nerves to the second, third, and fourth sacral nerves. Those from the lower portion of the birth canal pass pri marily through the Pudendal Nerve. Nerve. Anesthetic blocks used in in labor and delivery target this innervation. Ovaries During childbearing years: 2.5 -5 cm in length, 1.5-3 cm in breadth, and 0.6-1.5 cm in thickness. Usually lie in the upper part of the pelvic cavity Rest in a slight depression on the lateral w all of the pelvis (Ovarian Fossa of Waldeyer) Between the divergent external and internal iliac vessels. Uteroovarian Ligament Originates from the lateral and upper posterior portion of the uterus Beneath the tubal insertion level Extends to the uterine pole of the ovary 3-4 mm in diameter Made up of muscle and connective tissue covered by Mesovarium Blood supply traverses to and from the ovary through this double-layered mesovarium to enter the ovarian hilum. Consists of a cortex and medulla Young women: outermost portion of the cortex is smooth Tunica Albuginea: dull white surface
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Fallopian Tubes Called Oviducts Serpentine tubes extend 8-14 cm from the uterine cornua Anatomically classified classified along their length as an a) Interstitial Portion b) Isthmus c) Ampulla d) Infundibulum Interstitial Portion Most proximal Embodied within the uterine muscular wall. Isthmus Narrow 2-3 Mm Adjoins the uterus and and widens gradually Ampulla 5-8 mm More lateral Infundibulum funnel-shaped fimbriated distal extremity of the tube opens into the abdominal cavity Latter three extrauterine portions are covered by the Mesosalpinx at Mesosalpinx at the superior margin of the broad ligament. Extrauterine fallopian tube contains a mesosalpinx, myosalpinx, an d endosalpinx
Maternal Anatomy
Mesosalpinx Single-cell mesothelial layer Functioning as visceral peritoneum Myosalpinx Smooth muscle inner circular and an outer longitudinal longitudinal layer. Arranged in an inner In the distal tube, the two layers are less distinct and are replaced near the fimbriated extremity by sparse interlacing muscular fibers. Tubal musculature undergoes rhythmic contractions constantly, the rate of which varies with cyclical ovarian hormonal changes. Endosalpinx Tubal mucosa Single columnar epithelium composed of ciliated and secretory cells resting on a sparse lamina propria In close contact with the underlying myosalpinx. Ciliated cells are most abundant at the fimbriated extremity, but elsewhere, they are found in discrete patches Mucosa is arranged in longitudinal folds that become progressively more complex toward the fimbria Ampulla: lumen lumen is occupied almost completely completely by the arborescent mucosa Current produced by the tubal cilia is su ch that the direction of flow is toward the uterine cavity.
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Tubal peristalsis created by cilia and muscular layer contraction is believed to be an important factor in ovum transport Supplied richly with elastic tissue, blood vessels, and lymphatics. Sympathetic innervation is extensive in contrast to their parasympathetic innervation Nerve supply derives partly from the Ovarian Plexus and Plexus and partly from the Uterovaginal Plexus. Plexus. Sensory afferent fibers ascend to T10 spinal cord levels.
MUSCULOSKELETAL MUSCULOSKELETAL PELVIC ANATOMY
Pelvic Bones Pelvis Composed of four bones a) Sacrum b) Coccyx c) Two Innominate Bones Each innominate bone is formed by the fusion of three bones 1) Ilium 2) Ischium 3) Pubis Joined to the sacrum at the sacroiliac synchondroses and to one another at the symphysis pubis Conceptually divided into false and true components a) False Pelvis Lies above the linea terminalis Bounded: p:lumbar vertebra, l: iliac fossa, a:lower portion of the anterior abdominal wall b) True Pelvis Portion important in childbearing Obliquely truncated, bent cylinder with its greatest height posteriorly. Borders: S:linea terminalis I: pelvic outlet P: anterior surface of the sacrum L:inner surface of the ischial bones and the sa crosciatic notches and ligaments A: pubic bones, ascending ascending superior rami of the ischial ischial bones, and obturator foramina. Sidewalls converge Extending from the middle of the posterior margin of each ischium are the ischial spines. Great obstetrical importance because the d istance between them usually represents the shortest diameter of the true pelvis. Serve as valuable landmarks in assessing the level to which the presenting part of the fetus has descended into the true pelvis Aid pudendal nerve nerve block placement. Sacrum Forms the posterior wall of the true pelvis Upper anterior margin corresponds to the promontory that may be felt during bimanual pelvic examination in women with a small pelvis. Provide a landmark for clinical pelvimetry Normally, the sacrum has a marked vertical and a less pronounced horizontal concavity, which in abnormal pelves may undergo important variations. Straight line drawn from the promontory to the tip of the sacrum u sually measures 10 cm Distance along the concavity averages 12 cm
Pelvic Joints A: pelvic bones are are joined together by the the symphysis pubis. Consists of fibrocartilage and the superior and Inferior Pubic Ligaments. Rem
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Frequently designated the arcuate ligament of the pubis. P: pelvic bones are joined by articulations Between the sacrum and the iliac portion of the innominate bones to f orm the Sacroiliac Joints. Joints . These joints in general have a limited degree of mobility. During pregnancy, there is remarkable relaxation of these joints at term, caused by upward gliding of the sacroiliac joint Displacement, which is greatest in the dorsal lithotomy position, may increase the diameter of the outlet by 1.5-2.0 cm. Main justification for placing a woman in this position for a vaginal delivery. But this pelvic outlet diameter increase occurs only if the sacrum is allowed to rotate posteriorly. Thus, it will not occur if the sacrum is f orced anteriorly by the weight of the maternal pelvis against the delivery table or bed Sacroiliac joint mobility is also the likely reason that the McRoberts maneuver often is successful in releasing an obstructed shoulder in a case of shoulder dystocia modified squatting position to hasten hasten Attributed to the success of the modified second-stage labor Squatting position may increase the interspinous diameter and the pelvic outlet diameter
Planes and Diameters of the Pelvis Pelvis is described as having four imaginary planes: a) The plane of the pelvic inlet (Superior Strait) b) The plane of the pelvic outlet (Inferior Strait) c) The plane of the midpelvis: least pelvic dimensions d) The plane of greatest pelvic dimension: no obstetrical significance.
Pelvic Inlet the Superior Strait Also called the Superior plane of the true pelvis Bounded: P: promontory and alae of the sacrum L: linea terminalis pubic rami and the symphysis pubis. pubis. A: horizontal pubic During labor, fetal head engagement (fetal ( fetal head’s biparietal diameter ) passing through this plane. To aid this passage, the inlet of the female pelvis typically is more nearly round than ovoid. Nearly round or gynecoid pelvic inlet in approximately half of white women. Four diameters of the pelvic inlet are usually described: a) Anteroposterior b) Transverse c) Two oblique diameters Distinct anteroposterior diameters have been described using specific landmarks. a) Anteroposterior Diameter Diameter Most cephalad Termed the True Conjugate Extends from the uppermost margin of the symphysis pubis to the sacral promontory Clinically important Obstetrical Conjugate is Conjugate is the shortest distance between the sacral promontory and the symphysis pubis. Normally, this measures 10 cm or more, but cannot be measured directly with examining fingers. Estimated indirectly by subtracting 1.5-2 cm from the Diagonal Conjugate Determined by measuring the distance Transverse diameter is constructed at right angles to the obstetrical conjugate Represents the greatest distance between the linea terminalis on either side
Maternal Anatomy
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Usually intersects the obstetrical conjugate at a point approximately 5 cm in front of the promontory and measures approximately 13 cm. Each of the two oblique diameters extends from one sacroiliac synchondrosis to the contralateral iliopubic eminence. Each eminence is a minor elevation that marks the union site of the ilium and pubis. These oblique diameters average less than 13 cm.
Midpelvis and Pelvic Outlet Midpelvis Measured at the level of the ischial spines Also called the Midplane or Plane of Least Pelvic Dimensions During labor, the degree of fetal head descent into the tr ue pelvis may be described by station, and the midpelvis and ischial spines serve to mark zero station Interspinous Diameter 10 cm or slightly greater Usually the smallest pelvic diameter Anteroposterior Diameter Through the level of the ischial spines Normally measures at least 11.5 cm Pelvic Outlet Consists of two approximately triangular areas whose boundaries mirror those of the perineal triangle Base is a line drawn between the two ischial tuberosities Apex of the posterior posterior triangle is the tip of the sacrum Lateral boundaries are the sacrotuberous ligaments and the ischial tuberosities Anterior triangle is formed by the descending inferior rami of the pubic bones Rami unite at an angle of 90-100 degrees to f orm a rounded arch under which the fetal head must pass. Clinically, three diameters of the pelvic outlet usually are describe Anteroposterior Transverse Posterior sagittal Unless there is significant pelvic bony disease, the pelvic outlet seldom obstructs vaginal delivery.
Pelvic Shapes Caldwell-Moloy anatomical classification of the pelvis based on shape, and its concepts aid an understanding of labor mechanisms. Greatest transverse diameter of the inlet and its division into anterior and posterior segments are used to classify the pelvis as a) Gynecoid b) Anthropoid c) Android d) Platypelloid Posterior segment determines the type of pelvis Anterior segment determines the tendency. Both determined because many pelves are not pure but are mixed types. Gynecoid pelvis with an android tendency means that the po sterior pelvis is gynecoid and the anterior pelvis is an droid shaped. Configuration of the gynecoid pelvis would intuitively seem suited for delivery of most fetuses. Gynecoid pelvis was found in almost half of women.
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