Week 22 Anatomy

The bony pelvis.

  • Ischium
    • Ishial tuberoscity
    • Greater and lesser sciatic notch
    • Obturator foramen
    • Ischial spine
  • Ilium
    • Ala
    • Crest
    • ASIS, AIIS
  • Pubis
    • Symphysis
    • Tubercle, crest, superior and inferior rami


The rectum

Structures palpable on PR examination

  • POD in women
  • Prostate in men

Blood supply / venous drainage of the rectum / anus.

  • Superior rectal artery – from inferior mesenteric
  • Middle rectal artery – from inferior vesicle artery
  • Inferior rectal artery – from internal pudendal artery – supply external anal sphincter, anorectal junction and anal canal.
  • Superior, middle and inferior rectal vein, internal and external rectal venous plexuses.
  • Superior drains into portal while other 2 drain into systemic veins

Lymphatic drainage of the rectum / anus.

  • Superior half drain to pararectal LNs–> inferior mesenteric LNs–> drain to Lumbar(caval/aortic) LNs
  • Inferior half–>sacral LNs–> internal iliac LNs


The bladder / Control of micturition.

  • Sympathetics – relax detrusors and constrict urethral sphincter
  • Inferior thoracic and upper lumbar cord levels –> hypogastric plexus –> vesicle plexus
  • Parasympathetic – contract detrusors and relax urethral sphincter
  • Sacral spinal cord segments –> pelvic splanchnic nerves and inferior hypogastric plexus
  • Sensory afferents follow parasympathetic fibres


The male urethra.

  • 18-22cm long
  • Four parts
  • Intramural 0.5-1.5cm
  • Prostatic 3-4cm widest
  • Membranous 1-1.5cm narrowest
  • Spongy 15cm


Sacroiliac joint

  • The sacroiliac joint or SI joint (SIJ) is the joint in the bony pelvis between the sacrum and the ilium of the pelvis.
  • Joined by strong ligaments.
  • Sacrum supports the spine and is supported in turn by an ilium on each side.
  • The joint is a strong, weight bearing synovial plane joint with irregular elevations and depressions that produce interlocking of the two bones.