Updated: 11/27/2016

Pectinate Line

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Overview
pectinate line
  • Anal canal
    • divided into upper 2/3 (visceral portion) that belongs to the intestines and lower 1/3 (somatic portion) that belongs to the perineum
    • upper 2/3 is derived from the hindgut, endodermal in origin
    • lower 1/3 is derived from the proctodeum, ectodermal in origin
    • pectinate (dentate) line is the junction between endoderm and ectoderm and is located at the inferior limit of the anal valves
      • pectinate line divides the visceral and somatic portion
  • Upper 2/3
    • above pectinate line
    • simple columnar epithelium
      • upper 2/3 anal canal is the site of adenocarcinoma
    • arterial supply via the superior rectal artery, a continuation of IMA
    • venous drainage
      • superior rectal vein → inferior mesenteric vein → portal system
    • lymphatic drainage to the internal iliac lymph nodes
    • internal hemorrhoids
      • occur above the pectinate line and are covered by the mucous membrane
      • receive visceral innervation and therefore are not painful
      • may be a sign of portal hypertension
  • Lower 1/3
    • below pectinate line
    • stratified squamous epithelium
      • lower 1/3 of the anal canal is the site of squamous cell carcinoma
    • arterial supply via the inferior rectal arteries, branches of the internal pudendal arteries
    • venous drainage
      • inferior rectal vein → internal pudendal vein → internal iliac vein → IVC
    • lymphatic drainage to the superficial inguinal lymph nodes
    • external hemorrhoids
      • occur below the pectinate line and are covered by the skin
      • receive somatic innervation by the inferior rectal nerve, a branch of the pudendal nerve, and therefore are painful

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