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pectinate line

(dentate line) A visible zig-zagging line formed by the anal columns or anal valves. It divides the upper two-thirds and lower third of the anal canal. Developmentally, it represents the hindgut-proctodeum junction. (Tissues) • Upper: Columnar epithelium, derived from the endodermal hindgut. • Lower: Stratified squamous epithelium, non-keratinized, derived from the ectodermal proctodeum. (Vessels) • Upper: Supplied by superior rectal artery. Draining from superior rectal vein, into the inferior mesenteric vein, and subsequently the hepatic portal system. And draining via internal iliac lymph nodes (hypogastric lymph nodes). • Lower: Supplied by middle and inferior rectal arteries. Draining via middle and inferior rectal veins. And draining via superficial inguinal lymph nodes (below Hilton's white line). (Nerves) • Upper: Innervated by inferior hypogastric plexus. Internal hemorrhoids are not painful. • Lower: Innervated by pudendal nerves. External hemorrhoids are painful.