Pelvic Anatomy and Landmarks

Bony Landmarks

• Iliac crest, iliac tubercle, ASIS, AIIS, Obturator canal, obturator membrane, greater sciatic notch, superior pubic ramus, ischial spine, lesser sciatic notch, ischial tuberosity, inferior pubic ramus, ischial ramus, ischiopubic ramus

Pelvic Ligaments

• Posterior sacroiliac ligament, Sacrotuberous ligament, Sacrospinous ligament, Anterior sacroiliac ligament

Perineum

• The perineum consists of the pelvic outlet caudal to the pelvic diaphragm.
• A line joining the anterior parts of the ischial tuberosities divides the perineum into the:
  • Posterior Anal triangle
  • Anterior Urogenital triangle

Pelvic Diaphragm

• Separates the pelvic cavity from the perineum.
• Supports pelvic viscera.
• Provides sphincteric action at the anorectal junction for fecal continence.
• Helps resist increased intra-abdominal pressure during activities like coughing and defecating.
• Composed of:
  • Levator ani muscle:
    • Puborectalis
    • Pubococcygeus
    • Iliococcygeus
  • (Ischio) Coccygeus

Ischiorectal Fossa

• Wedge-shaped, fat-filled regions surrounding the anal canal.
• Located between the skin of the anal region and the pelvic diaphragm.
• Boundaries:
  • Base: Skin and fascia
  • Apex: Obturator internus muscles meet the levator ani muscle
  • Lateral wall: Ischium, inferior part of obturator internus and its fascia (encloses the pudendal (Alcock's) canal with pudendal nerve and vessels)
  • Medial wall: Anal canal, covered externally by the external anal sphincter and sloping levator ani muscle
  • Anteriorly: Urogenital diaphragm
  • Posteriorly: Gluteus maximus muscle

Anal Sphincter

• The anal canal is held closed by the external and internal anal sphincters.
  • External anal sphincter:
    • Voluntary
    • Skeletal muscle surrounding the lower two thirds of the anal canal
    • Consists of three parts:
      • Subcutaneous
      • Superficial
      • Deep (profundus)
  • Internal anal sphincter:
    • Involuntary
    • Occupies the upper two thirds of the anal canal down to Hilton's line
    • Formed by a thickening of the inner circular layer of smooth muscle
    • Sympathetic stimulation contracts the muscle; parasympathetic stimulation relaxes it

Anal Canal

• Measures approximately 4 cm in length.
• Superior 2/3:
  • Lined by columnar epithelium
  • Innervation: Autonomic
  • Responsive to stretch
  • Characterized by vertical folds called anal columns joined together by anal valves
• Inferior 1/3:
  • Lined by stratified squamous epithelium
  • Innervation: Somatic - inferior rectal nerves
  • Responsive to pain, touch, and temperature
  • Lymphatic drainage to superficial inguinal nodes

Hemorrhoids (Piles)

• Internal:
  • Dilated internal venous plexus of the superior rectal vein
  • Occur above the pectinate line, painless
  • Typically seen at 3, 7, and 11 o'clock in the lithotomy position
• External:
  • Varicosities of the inferior rectal veins
  • Occur below the pectinate line, painful due to somatic innervation
  • Often blood clots under the skin in the external rectal venous plexus

Explore the key bony landmarks, ligaments, and structures of the pelvic region. This quiz covers important aspects such as the pelvic diaphragm and perineum, focusing on their functions and anatomical features. Test your knowledge of pelvic anatomy and its relevance to human physiology.