Page 410 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

366 seCtion iii Gastrointestinal ` gastrointestinal—anatomy Gastrointestinal ` gastrointestinal—anatomy

Pectinate line Also called dentate line. Formed where endoderm (hindgut) meets ectoderm.
Nerves Arteries Veins Lymphatics Above pectinate line: internal hemorrhoids,
Visceral innervation Superior rectal Superior rectal vein Drain to internal adenocarcinoma.
artery (branch → IMV → splenic iliac LN Internal hemorrhoids receive visceral
of IMA) vein → portal vein
innervation and are therefore not painful.

Pectinate line
Below pectinate line: external hemorrhoids,
anal fissures, squamous cell carcinoma.
External hemorrhoids receive somatic
innervation (inferior rectal branch of
pudendal nerve) and are therefore painful if
thrombosed.
Anal fissure—tear in anal mucosa below
Inferior rectal vein Pectinate line. Pain while Pooping; blood
Inferior rectal artery → internal pudendal Drain to superficial on toilet Paper. Located Posteriorly because
Somatic innervation (branch of internal vein → internal iliac inguinal LN
pudendal artery) vein → common iliac this area is Poorly Perfused. Innervated by
vein → IVC Pudendal nerve. Associated with low-fiber
diets and constipation.

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