TOPICS: Hindgut, endoderm, ectoderm, superior rectal vein, inferior mesenteric vein, portal network, superior rectal artery, inferior mesenteric artery (IMA), internal iliac lymph nodes, superficial inguinal lymph nodes, somatic innervation, visceral innervation, inferior rectal vein, inferior rectal artery, internal iliac artery, internal iliac vein, internal pudendal vein, hemorrhoids, azygos vein, esophageal vein, left gastric veins, short gastric vein, portal vein, splenic vein, superior mesenteric vein (SMV), inferior mesenteric vein (IMV), varices, superficial epigastric vein, internal iliac vein, internal pudendal vein, periumbilical vein, lymphatic system, cervical lymph nodes, thoracic duct, thymus, axillary lymph nodes, lymphatics of the mammary gland, cisterna chyli, spleen, lumbar lymph nodes, pelvic lymph nodes, lymphatics of the upper limb, inguinal lymph nodes, lymphatics of the lower limb, adenocarcinoma, squamous cell carcinoma, pudendal nerve, somatic, visceral, above pectinate line, below pectinate line