Pelvic Viscera PDF

Pelvic Viscera DPM 1. Describe the characteristics of the rectum. 2. Describe the anal canal and ischioanal fossae. 3. Compare and contrast the anal canal above the pectinate line and below the pectinate line in terms of arterial supply, venous drainage, and innervation. 4. Compare and contrast the...

Pelvic Viscera DPM 1. Describe the characteristics of the rectum. 2. Describe the anal canal and ischioanal fossae. 3. Compare and contrast the anal canal above the pectinate line and below the pectinate line in terms of arterial supply, venous drainage, and innervation. 4. Compare and contrast the internal and external anal sphincters in terms of location, structure, and innervation. 5. Describe the differences between internal and external hemorrhoids. 6. Describe the location of the ureters and relationships. 7. Describe the characteristics of the bladder. 8. Describe the apex and base of the bladder and all associated structures. 9. Describe the neck of the bladder and the associated fibromuscular bands. 10. Describe the urethra and differences in male and female. 1 SMU - Internal Data Introduction to pelvic viscera. The pelvic viscera include parts of the gastrointestinal system, the urinary system, and the reproductive system. The viscera are arranged in the midline, from front to back; the neurovascular supply is through branches that pass medially from vessels and nerves associated with the pelvic walls. Gastrointestinal system Pelvic parts of the gastrointestinal system consist mainly of the rectum and the anal canal, although the terminal part of the sigmoid colon is also in the pelvic cavity 2 SMU - Internal Data Describe the characteristics of the rectum. Rectum The rectum is continuous: ▪ above, with the sigmoid colon at about the level of vertebra SIII ▪ below, with the anal canal as this structure penetrates the pelvic floor and passes through the perineum to end as the anus The rectum, the most posterior element of the pelvic viscera, is immediately anterior to and follows the concave contour of the sacrum. The anorectal junction is pulled forward (perineal flexure) by the action of: • the puborectalis part of the levator ani muscle • the anal canal moves in a posterior direction as it passes inferiorly through the pelvic floor S3 3 SMU - Internal Data In addition to conforming to the general curvature of the sacrum in the anteroposterior plane, the rectum has three lateral curvatures: 1. the upper and lower curvatures to the right 2. the middle curvature to the left Sigmoid colon Upper curvature Middle curvature The lower part of the rectum is expanded to form the rectal ampulla. Finally, unlike the colon, the rectum lacks distinct taeniae coli muscles, omental appendices, and sacculations (haustra of the colon). Lower curvature 4 SMU - Internal Data Describe the anal canal and ischioanal fossae. The anal canal is an inferior continuation of the rectum. It begins at the superior edge of the levator ani (and superior limit of anal columns). Obturator internus muscle and fascia The ischioanal fossae surround the wall of the anal canal. They are wedgeshaped, fat-filled regions that lie between the skin of the anal region and the pelvic diaphragm. These fossae allow for expansion of the anal canal Pudendal canal with nerves and vessels Ischial tuberosity Ischioanal fossa Internal anal External anal sphincter sphincter 5 SMU - Internal Data Anal canal and sphincters. Superior two-thirds of the anal canal: • • • Is derived from hindgut (endodermal lining creating mucosa) Is viscerally innervated (GVA, GVE) has anal columns (vertical folds created by tributaries to the superior rectal v.). These columns are joined together by semilunar folds called anal valves The Pectinate Line is Located approximately at the junction between the superior 2/3’s and inferior 1/3 of the anal canal (demarcated anatomically by the anal valves and the inferior limit of the anal columns). It represents the termination of the gut-derived viscera. Anal sinus Levator ani muscle Anal column Anal valves Inferior 1/3 of the anal canal: • • Ectodermal lining (creating skin) somatically innervated (GSA, GSE). Internal Anal Sphincter: • Involuntary • Formed by a thickening of the inner circular layer of smooth muscle External Anal Sphincter: • Voluntary • Skeletal muscle that encloses the distal anal canal. Some of it’s deeper fibers merge with those of the puborectalis portion of the levator ani. External anal sphincter Anal canal Internal anal sphincter Pectinate line 6 SMU - Internal Data Blood supply of the anal canal. Superior rectal vein (a branch of inferior mesenteric vein) Superior rectal a. Internal iliac a. Middle rectal a. Obturator internus muscle Internal pudendal vein Internal pudendal a. Middle rectal vein Inferior rectal a. (branch of internal pudendal a.) Inferior rectal vein Superior rectal a./v. - from/to IMA/IMV (portal) - terminate inside the anal columns, supplies region above pectinate line Middle rectal a./v. - from/to Internal iliac a./v. (caval) - anastomose with both superior and inferior rectal vessels Inferior rectal a./v. - from/to Internal pudendal a./v. (caval) - supplies region below pectinate line 7 SMU - Internal Data Describe the differences between internal and external hemorrhoids. Internal: Tributary of superior rectal vein Anal column Internal anal sphincter Prolapsed rectal mucosa containing the (normally) dilated internal venous plexus of veins that are tributaries of the superior rectal vein . Internal hemorrhoid Occur above the pectinate line, so are painless. External anal sphincter Anal valves Mucous membrane Perianal hematoma External hemorrhoid External: Varicosities of the inferior rectal veins. Often blood will clot under the skin in the external rectal venous plexus (branches of inferior rectal). 11 o’clock 3 o’clock These occur below the pectinate line, receive somatic innervation, so are painful. 7 o’clock 8 SMU - Internal Data Describe the location of the ureters and relationships. Urinary system The pelvic parts of the urinary system consist of the terminal parts of the ureters, the bladder, and the proximal part of the urethra. Do you remember the Ureters? The ureters enter the pelvic cavity from the abdomen by passing through the pelvic inlet. On each side, the ureter crosses the pelvic inlet and enters the pelvic cavity in the area anterior to the bifurcation of the common iliac artery. Right ureter Left ureter Ovarian/testicular vessels Common iliac artery From this point, it continues along the pelvic wall and floor to join the base of the bladder. In the pelvis, the ureter is crossed by: ▪ the ductus deferens in men ▪ the uterine artery in women 9 SMU - Internal Data 10 SMU - Internal Data 11 SMU - Internal Data Describe the characteristics of the bladder. Bladder • the most anterior element of the pelvic viscera • although it is entirely situated in the pelvic cavity when empty, it expands superiorly into the abdominal cavity when full. The empty bladder is shaped like a three-sided pyramid that has tipped over to lie on one of its margins. It has an apex, a base, a superior surface, and two inferolateral surfaces. 12 SMU - Internal Data Describe the apex and base of the bladder and all associated structures. Apex of the bladder • directed toward the top of the pubic symphysis • a structure known as the median umbilical ligament (a remnant of the embryological urachus that contributes to the formation of the bladder) continues from it superiorly up the anterior abdominal wall to the umbilicus Base of bladder • The base of the bladder is shaped like an inverted triangle and faces posteroinferiorly • The two ureters enter the bladder at each of the upper corners of the base, and the urethra drains inferiorly from the lower corner of the base • Inside, the mucosal lining on the base of the bladder is smooth and firmly attached to the underlying smooth muscle coat of the wall—unlike elsewhere in the bladder where the mucosa is folded and loosely attached to the wall • The smooth triangular area between the openings of the ureters and urethra on the inside of the bladder is known as the trigone SMU - Internal Data 13 Describe the neck of the bladder and the associated fibromuscular bands. Neck of bladder • surrounds the origin of the urethra at the point where the two inferolateral surfaces and the base intersect. • most inferior part of the bladder and also the most “fixed” part. • it is anchored into position by a pair of tough fibromuscular bands, which connect the neck and pelvic part of the urethra to the posteroinferior aspect of each pubic bone. • In women, these fibromuscular bands are termed: • pubovesical ligaments • with the perineal membrane and associated muscles, these ligaments help support the bladder. • SMU - Internal Data In men, the paired fibromuscular bands are known as: • puboprostatic ligaments • they blend with the fibrous capsule of the prostate, which surrounds the neck of the bladder and adjacent part of the urethra 14 Describe the urethra and differences in male and female. Male Female Body of bladder Ureteric orifice Urethra Preprostatic urethra Prostatic urethra Intermediate urethra Vagina Spongy urethra Vestibule of vagina Urethra The urethra begins at the base of the bladder and ends with an external opening in the perineum. The paths taken by the urethra differ significantly in women and men. 15 SMU - Internal Data Urethra in women: • In women, the urethra is short, being about 4 cm long • It travels a slightly curved course as it passes inferiorly through the pelvic floor into the perineum, where it passes through the deep perineal pouch and perineal membrane before opening in the vestibule that lies between the labia minora Urethral opening: • anterior to the vaginal opening in the vestibule • inferior aspect of the urethra is bound to the anterior surface of the vagina • two small para-urethral mucous glands (Skene's glands) are associated with the lower end of the urethra • each drains via a duct that opens onto the lateral margin of the external urethral orifice Urethral opening Vaginal opening 16 SMU - Internal Data Urethra in men: • the urethra is long, about 20 cm, and bends twice along its course • Beginning at the base of the bladder and passing inferiorly through the prostate, it passes through the deep perineal pouch and perineal membrane and immediately enters the root of the penis • As the urethra exits the deep perineal pouch, it bends forward to course anteriorly in the root of the penis • When the penis is flaccid, the urethra makes another bend, this time inferiorly, when passing from the root to the body of the penis • During erection, the bend between the root and body of the penis disappears The urethra in men is divided into preprostatic, prostatic, membranous, and spongy parts. 17 SMU - Internal Data Preprostatic part • about 1 cm long • extends from the base of the bladder to the prostate • is associated with a circular cuff of smooth muscle fibers (the internal urethral sphincter). • contraction of this sphincter prevents retrograde movement of semen into the bladder during ejaculation Prostatic part • prostatic part of the urethra is 3 to 4 cm long and is surrounded by the prostate • on each side of the prostatic utricle is the opening of the ejaculatory duct of the male reproductive system • Therefore, the connection between the urinary and reproductive tracts in men occurs in the prostatic part of the urethra. 18 SMU - Internal Data Membranous part • membranous part of the urethra is narrow and passes through the deep perineal pouch • during its transit through this pouch, the urethra is surrounded by skeletal muscle of the external urethral sphincter Spongy urethra • spongy urethra is surrounded by erectile tissue (the corpus spongiosum) of the penis • the two bulbo-urethral glands in the deep perineal pouch are part of the male reproductive system and open into the bulb of the spongy urethra • the external urethral orifice is the sagittal slit at the end of the penis 19 SMU - Internal Data