Gross Anatomy: Pelvic Cavity PDF 2025

Gross Anatomy: Pelvic Cavity Page 1 of 15 Dr. Mark Ireland SESSION LEARNING OBJECTIVES By the end of this session, students should be able to accurately: 1. Describe the walls of the pelvic cavity. 2. List and describe the arteries of the...

Gross Anatomy: Pelvic Cavity Page 1 of 15 Dr. Mark Ireland SESSION LEARNING OBJECTIVES By the end of this session, students should be able to accurately: 1. Describe the walls of the pelvic cavity. 2. List and describe the arteries of the pelvic cavity differentiating those that arise from the posterior vs. anterior trunks of the internal iliac artery and specifying differences between male and female. 3. Describe the veins of the pelvic cavity. 4. Describe the lymphatics of the pelvic cavity. 5. Describe the nerves of the pelvic cavity and their distribution within and outside the pelvis. 6. Describe the pelvic fascia including specializations of parietal and visceral fascia. 7. Relate pelvic structures to the peritoneum. 8. Describe the anatomy of the rectum and anal canal: arteries, veins, lymphatics, innervation, and clinical considerations. SUPPLEMENTAL READING Gray’s Anatomy for Students, 4th Ed (2020) Drake, Vogl, Mitchell (Elsevier) Chapter 5. Gross Anatomy: Pelvic Cavity Page 2 of 15 Dr. Mark Ireland SESSION OUTLINE I. Walls of the Pelvic Cavity II. Arteries of the Pelvic Cavity A. Arising from Posterior Trunk of Internal Iliac B. Arising from Anterior Trunk of Internal Iliac – Male C. Arising from Anterior Trunk of Internal Iliac – Female III. Veins IV. Lymphatics V. Nerves A. Sacral Plexus B. Coccygeal Plexus C. Obturator Nerve D. Sympathetic Nerves E. Parasympathetic Nerves VI. Endopelvic Fascia – Visceral and Parietal VII. Peritoneum VIII. Rectum and Anal Canal A. Arteries B. Veins C. Lymphatics D. Innervations E. Hemorrhoids – Clinical Considerations Gross Anatomy: Pelvic Cavity Page 3 of 15 Dr. Mark Ireland I. WALLS OF THE PELVIC CAVITY (Fig 1 Gray’s 5.34) Anterior →pubic bone and pubic symphysis →anterior portions of levator ani mm. Fig 1 Lateral →ilium, ishium →obturator internus m. and fascia →lateral portions of levator ani →medial to obturator internus m. are the obturator a. and n. and other branches of the internal iliac a. Posterior →sacrum, coccyx, sacroiliac joint, sacrotuberous lig., and sacrospinous lig. →piriformis and coccygeus mm. →medial to the piriformis m. are the sacral plexus, autonomic plexuses and branches of the internal iliac a. Gross Anatomy: Pelvic Cavity Page 4 of 15 Dr. Mark Ireland Fig 2 Inferior (Fig 2 Gray’s 5.36C) →urogenital diaphragm →puborectalis II. ARTERIES OF THE PELVIS Arising from the Internal Iliac A. – Tremendous variation in this pattern Fig 3 Posterior Trunk (Fig 3 Gray’s 5.64) iliolumbar - posterior abdominal wall and iliac fossa lateral sacral – pass through anterior sacral foramina to supply sacral canal superior gluteal – usually passes out of pelvis between lumbosacral trunk and anterior ramus of S1 above piriformis to supply gluteal muscles and skin Gross Anatomy: Pelvic Cavity Page 5 of 15 Dr. Mark Ireland Fig 4 Anterior Trunk-Male (Fig 4 Gray’s 5.65A) umbilical – vestigial remnant which carried blood from fetus to placenta superior vesical – usually arises from umbilical to supply superior bladder and distal ureter inferior vesical – supplies the inferior bladder, seminal vesical, prostate, ureter middle rectal – courses medially to rectum; anastomoses with the superior (from the inferior mesenteric a.) and inferior rectals (from the internal pudendal a.) obturator – accompanies obturator n. to supply medial thigh; often originates from external iliac a. or inferior epigastric a. internal pudendal – exits the pelvis through the greater sciatic foramen inferior to the piriformis; passes through lesser sciatic foramen with the pudendal nerve to enter and supply the perineum inferior gluteal – exits the pelvis through greater sciatic foramen inferior to the piriformis; passes between S1 and S2 or S2 and S3 anterior rami; supplies gluteal region and hip joint Other Sources external iliac – often the origin of obturator a. as it passes superior to the pelvic brim gonadal – testicular or ovarian aa. arise from abdominal aorta; ovarian travels in the suspensory ligament of the ovary while the testicular enters the inguinal canal median sacral – from near the bifurcation of the aorta; anastomoses with the lateral sacral and iliolumbar aa. superior rectal – last branch of the inferior mesenteric a.; supplies rectum and upper anal canal; anastomoses with middle and inferior rectal aa. Gross Anatomy: Pelvic Cavity Page 6 of 15 Dr. Mark Ireland Anterior Trunk-Female (Fig 5 Gray’s 5.65B) Fig 5 uterine – courses in the broad ligament to reach the cervix; ascends lateral to the uterus to reach the uterine tube where it anastomoses with the ovarian a.; passes superior to the ureter vaginal – usually a branch of the uterine but may be a separate branch of the anterior trunk; will supply the vagina, bladder and rectum; takes the place of an inferior vesical seen in the male Gross Anatomy: Pelvic Cavity Page 7 of 15 Dr. Mark Ireland III. VEINS (Fig 6 Gray’s 5.67A) →Numerous, inter- connected venous Fig 6 plexuses are found on the surface of the pelvic organs. Therefore, there are rectal, prostatic, uterine, vaginal and vesical plexuses. Since these veins have no valves (ie. blood can flow in either direction) and due to their connections with vertebral venous plexuses and lumbar veins, there is a potential for the extensive spread of infection or cancer. →These plexuses eventually form veins with the same name as their accompanying arteries. These veins drain into the internal iliac v. which drains into the inferior vena cava. →Anastomoses exist between the middle/inferior rectal vv. and the superior rectal v. which drains into the portal system. Thus, the rectal vv. are an important portal- systemic anastomosis. Gross Anatomy: Pelvic Cavity Page 8 of 15 Dr. Mark Ireland IV. LYMPHATICS (Fig 7 Gray’s 5.68) Fig 7 Lymphatic drainage of the pelvis and perineum ultimately drains into aortic nodes. However, inferior structures close to external surface (ie. lower vagina, lower anal canal, scrotum) drain into inguinal nodes first. V. Nerves (Gray’sTable 5-4) Sacral Plexus (Fig 8 Gray’s 5.61) – formed by the lumbosacral trunk (L4,5) Fig 8 and the anterior rami of S1-S4; located on the medial surface of the piriformis; motor and sensory to pelvis and lower limb Coccygeal plexus – small plexus derived from S4,5,Co; forms the sensory anococcygeal n. to the skin of the anal triangle Obturator n. – not a part of sacral plexus but passes through the pelvis to eventually innervate the medial thigh Gross Anatomy: Pelvic Cavity Page 9 of 15 Dr. Mark Ireland Sacral Plexus and Pelvic Nerves in situ (Fig 9 Gray’s 5.60) Fig 9 Major Branches of Sacral Plexus -Sciatic (L4-S3) – motor to posterior thigh, all of leg and foot -Posterior Femoral Cutaneous -Superior Gluteal (L4-S1) – motor to gluteus medius/minimus, tensor fascia lata -Inferior Gluteal (L5-S2) – motor to gluteus maximus -Pudendal (S2-4) – motor to external urethral and anal sphinchters, levator ani; sensory to skin of perineum, penis and clitoris -Pelvic Splanchnics (S2-4) - parasympathetics Minor Branches of Sacral Plexus -N. to obturator internus and superior gemellus -N. to quadratus femoris and inferior gemellus -N. to piriformis -Ns. to levator ani, coccygeus, external anal sphincter -Coccygeal plexus (via anococcygeal ns.)– sensory to perianal skin, sacrococcygeal joint Gross Anatomy: Pelvic Cavity Page 10 of 15 Dr. Mark Ireland Fig 10 Sympathetics (Fig 10 Gray’s 5.62) – the sympathetic chain continues into the pelvis as does the superior hypogastric plexus; the superior hypogastric plexus divides into a right and left hypogastric nn.; an inferior hypogastric plexus is then formed which distributes to the pelvic viscera and external genitalia; sympathetic sacral splanchnic nn. depart from the sympathethic ganglia to enter the hypogastric nerves/inferior hypogastric plexus Gross Anatomy: Pelvic Cavity Page 11 of 15 Dr. Mark Ireland Fig 11 Parasympathetics (Fig 11 Gray’s 5.63A) – arise from the anterior rami of S2-4 as pelvic splanchnic nn. to enter the inferior hypogastric plexus; distribute to pelvic viscera, external genitalia and the lower digestive tract up to the splenic flexure of the large intestine Gross Anatomy: Pelvic Cavity Page 12 of 15 Dr. Mark Ireland VI. PELVIC FASCIA Endopelvic fascia – a continuation of the extraperitoneal connective tissue encountered in the abdomen; when it envelops the pelvic organs (false capsules) it is considered to be visceral fascia; when it lines the muscular walls of the pelvis it is considered to be parietal fascia; visceral and parietal fasciae are continuous where pelvic walls and viscera meet Specializations of Parietal Fascia →tendinous arch of the levator ani – attachment of pelvic diaphragm →pudendal canal – derived from obturator fascia in the ishioanal fossa →superior and inferior fascia of the pelvic diaphragm – inferior fascia is continuous with the external anal sphincter and fuses with the fascia of the UG diaphragm Specializations of Visceral Fascia →neurovascular sheaths →fascial ligaments – help support pelvic organs; attach to the pelvic walls and the more centrally located viscera; often contain a neurovascular bundle or structures entering/leaving viscera; more on these in following lectures VII. PELVIC RELATIONS TO THE PERITONEUM (Fig 12 Gray’s 5.59) General Description-the peritoneum covering the abdominal organs continues into the pelvis and partially covers various surfaces of the pelvic organs; it forms pouches between adjacent pelvic organs and covers over fascial ligaments Fig 12 female→rectouterine pouch male→rectovesical pouch →vesicouterine pouch Gross Anatomy: Pelvic Cavity Page 13 of 15 Dr. Mark Ireland VIII. RECTUM AND ANAL CANAL (Fig 13, 14 Gray’s 5.39A, 5.67B) Fig 13 The rectum (Fig 13) extends from the rectosigmoid junction (~SV3) to the anorectal junction (where the rectum passes through the pelvic diaphragm). It follows the contour of the sacrum (sacral flexure) and is pulled anterior by the puborectalis as it passes through the pelvic diaphragm. The rectum has three lateral flexures, 2 to the right and one to the left, marked internally by transverse rectal folds (Fig 14). The ampulla is the most distal and distensible part of the rectum. The rectum is normally empty except just prior to defecation. The most superior part is covered Fig 14 anteriorly and laterally by peritoneum to form pararectal fossae. The rectum has no mesentery, taenia coli, haustra or epiploic appendages. Gross Anatomy: Pelvic Cavity Page 14 of 15 Dr. Mark Ireland Fig 15 The anal canal (Fig 15 Gray’s 5.39B) extends from the anorectal junction to the anus. Its mucosal lining is thrown into a series of anal columns, valves and sinuses at the pectinate line. Distal to the pectinate line is where the epithelial lining gradually changes into stratified, keratinized skin. The anal aperture is controlled by the internal (parasympathetic innervation) and external (voluntary) anal sphincters. A portion of the external sphincter (deep part) is derived from the puborectalis m. Arteries →above pectinate line – superior and middle rectal a. →below pectinate line - inferior rectal a. Veins (Fig 16 Gray’s 5.67B) →above pectinate line - superior rectal v. into inferior mesenteric v. and middle Fig 16 rectal v. into internal iliac v. →below pectinate line – inferior rectal v. into internal iliac v. →veins freely anastomose to form 2 venous plexuses internal rectal plexus – located between internal sphincter and mucosal covering of anal canal; drains into the superior rectal v. external rectal plexus – surrounds the external sphincter and drains into middle and inferior rectal vv. Important site of portal- caval anastomoses Gross Anatomy: Pelvic Cavity Page 15 of 15 Dr. Mark Ireland Lymphatics upper rectum→inferior mesenteric nodes→aortic nodes inferior rectum and anal canal above pectinate line→internal iliac nodes anal canal below pectinate line→superficial inguinal nodes Innervation above the pectinate line -vasomotor to blood vessels → sympathetics -smooth muscle including internal anal sphincter → parasympathetics via pelvic splanchnics cause relaxation while sympathetics cause contraction -sensory fibers for distention → pelvic splanchnics (parasympathetics) -relatively insensitive to pain below the pectinate line -motor to external anal sphincter (voluntary) → pudendal n. and branches from sacral plexus -sensation (pain, temperature, touch) → pudendal n. Clinical Considerations Internal hemorrhoids – dilations of the internal venous plexus above the pectinate line involving the superior rectal vv.; covered with mucosa; not painful initially but they do bleed and may become strangulated External hemorrhoids – dilations of the external venous plexus below the pectinate line involving the inferior rectal vv.; covered with stratified squamous epithelium; highly innervated; painful and itchy; may contain blood clots