Lecture Notes - Rectum, Anal Canal, & Pelvic Floor

Bony Structure

• 2 hip bones: ilium, pubis, ischium
• 1 sacrum
• 1 coccyx

Ligaments - hold/bind bony pelvis together and hold pelvis in proper orientation to resist forces
• sacrotuberous
• sacrospinous
• sacroiliac
Orientation - NOT a basin!!! Tilt to ~80° angle
• Pubic tubercles and ASIS in vertical line

Peritoneum

Falls short - does not reach pelvic floor/diaphragm
• Pouches
  • Female - vesicouterine & rectouterine
  • Male - rectovesical
• Broad Ligament - mesosalpinx, mesovarium, & mesometrium

Viscera

Rectum
• peritoneal covering - top 1/3 on front and sides, middle 1/3 on front, inferior 1/3 none
• transverse rectal folds
• passes through pelvic diaphragm to become anal canal
• blood supply and venous return - portocaval anastomosis
Anal Canal
• internal anal sphincter - thickened circular (smooth) muscle
• external anal sphincter - skeletal muscle
• anal columns, valves, and sinuses - what forms columns?
  • Pectinate line - functional significance??
Vessels
• Common iliacs
  • External iliacs - vessel of lower limb
  • Internal iliacs - pelvis, gluteals, medial thigh, perineum
• Internal iliac - highly variable!!
  • posterior division - parietal branches only
    • iliolumbar
    • lateral sacral
    • superior gluteal
  • anterior division - parietal and visceral branches
    • inferior gluteal
    • obturator (30% aberrant)
    • internal pudendal (around sacrospinous ligament)
    • umbilical (1st branch off anterior division)
    • superior vesical (artery of the ductus deferens)
    • middle rectal
    • inferior vesical (prostatic branches)
    • uterine (relationship to ureter!!)
    • vaginal
Innervation
• Sacral Plexus
  • ventral primary rami of L4,5 (aka, lumbosacral trunk) and S1,2,3,4
  • relationship to piriformis muscle
• Autonomics
  • Inferior hypogastric plexus (sides of rectum) - continuation of preaortic plexus via hypogastric nerves
  • Sacral splanchnics - sympathetic fibers from sacral portion of sympathetic chain
  • Pelvic splanchnics - parasympathetic fibers from S2,3,4
Review Intro to Autonomics Module - this is the time to make it all come together!
Also, review the formation of the inferior hypogastric plexus (Pelvic Autonomics Module)
• where do sympathetics come from?
• where do parasympathetics come from?
• how are specific pelvic viscera innervated?
Pelvic diaphragm/floor
• Wall of pelvic cavity
  • Obturator internus m.
    • Arcus tendineus levator ani - attachment for portion of levator ani m.
  • Piriformis m. - exits pelvis via greater sciatic foramen, sacral plexus lays on piriformis
• Floor or diaphragm
  • Above = pelvic cavity
  • Below = perineum
    • Coccygeus m. - on internal surface of sacrospinous ligament
    • Levator Ani m.
      • pubococcygeus
      • iliococcygeus
      • puborectalis
      • genital hiatus
  Perineum - inferior to pelvic diaphragm
  • Anal Triangle
    • ischioanal fossae - lateral to anal canal
      • obturator internus muscle is lateral wall
    • pudendal canal - fascia of obturator internus muscle
      • contains internal pudendal vessels & pudendal nerve
    • anal canal - review anal canal - internal structures and sphincter muscles
  • Urogenital Triangle
    • Perineal Membrane - bands of connective tissue between midline viscera and ischiopubic rami; erectile tissues attached to caudal surface

  Female	Male
  2 corpora cavernosa shaft of clitoris diverge as 2 crura along ischiopubic rami crura covered by ischiocavernosus muscle	2 corpora cavernosa shaft of penis diverges as 2 crura crura covered by ischiocavernosus m.
  2 vestibular bulbs glans of clitoris covered by bulbospongiosus m. greater vestibular glands	1 corpus spongiosus glans of penis spongy urethra bulb covered by bulbospongiosus m.
  perineal body muscle fibers from: bulbospongiosus, external anal sphincter & superficial transverse perineal	central tendinous point mm. fibers from: bulbospongiosus, ext. anal sphincter & superficial transverse perineal
  sphincter urethrae (urethrovaginal sphincter & compressor urethrae)	sphincter urethrae bulbourethral glands

  
  
  Pudendal Nerve
  • motor to all perineal muscles and sensory to most perineal structures
  • 3 branches
    • inferior rectal - external anal sphincter and skin around anus
    • perineal - posterior labial/scrotal branches and deep branch which is motor to transverse perineus mm., ischiocavernosus, bulbospongiosus, sphincter urethrae mm.
    • dorsal nerve of clitoris/penis - continuation of pudendal within sphincter urethrae m.; pierces membrane at anterior border and runs with dorsal aa. and v.
  Internal Pudendal Artery
  • branches
    • inferior rectal - anastomoses with which vessels?
    • perineal - superficial; terminates as posterior labial/scrotal
    • internal pudendal - runs within sphincter urethrae muscle with dorsal n. of clitoris/penis
      • 2 terminal branches
        • deep artery of clitoris/penis - within corpus cavernosum
        • dorsal artery of clitoris/penis - with nerves and vein