Hepatic Portal System Lecture Notes

Overview of Circulation

• Normal Circulation

  • Heart pumps blood through arteries → arterioles → capillaries
  • Gas and fluid exchange occurs in capillaries
  • Blood returns via venules → veins → heart

• Hepatic Portal System

  • Heart pumps blood → arteries → arterioles → first capillary bed
  • Venules drain capillaries into hepatic portal veins
  • Veins drain into a second capillary bed within the liver (hepatic sinusoids)
  • Blood drains into terminal hepatic venules → hepatic veins → inferior vena cava → heart
  • Unique feature: Two capillary beds in series

Anatomy Related to Hepatic Portal System

• Illustration Components
  • Liver, esophagus, stomach, spleen, small intestines (jejunum/ileum), large intestine
  • Blood flows via hepatic portal vein into liver parenchyma, then hepatic veins, inferior vena cava, heart

Blood Drainage

• Foregut

  • Drains: distal esophagus, stomach, parts of duodenum, liver, gallbladder, pancreas, spleen
  • Veins: gastric veins (left & right), gastro-omental (epiploic), splenic vein

• Midgut

  • Drains: duodenum (parts 2-4), jejunum, ileum, cecum, appendix, ascending/transverse colon
  • Veins: superior mesenteric vein

• Hindgut

  • Drains: transverse/descending colon, sigmoid colon, rectum
  • Veins: inferior mesenteric vein → splenic vein → hepatic portal vein

Characteristics of Hepatic Portal System

• Lacks valves → blood flow direction depends on pressure gradient

Portocaval Anastomosis

• Definition: Areas where blood drains into both the hepatic portal system and caval veins
• Key Areas:
  • Distal Esophagus
  • Rectum
  • Superficial Abdomen

Detailed Explanations

• Distal Esophagus

  • Portal drainage: left gastric vein → hepatic portal vein
  • Caval drainage: esophageal veins → azygos vein → superior vena cava
  • Implication: Portal hypertension can cause esophageal varices

• Rectum

  • Portal drainage: superior rectal vein → inferior mesenteric vein → splenic vein → hepatic portal vein
  • Caval drainage: middle/inferior rectal veins → internal iliac vein → common iliac vein → inferior vena cava
  • Implication: Portal hypertension can lead to internal hemorrhoids

• Anterior Abdominal Wall

  • Caval drainage: superficial epigastric veins → femoral vein → external iliac vein → common iliac → inferior vena cava
  • Portal drainage: peri-umbilical veins → round ligament → liver → portal vein
  • Implication: Portal hypertension can cause caput medusa

Summary of Portocaval Anastomosis

• Three Regions: "Gut, Butt, and Kaput"
  • Gut: Distal esophagus (portal & caval drainage)
  • Butt: Rectum (portal & caval drainage)
  • Kaput: Abdominal wall (caput medusa)