Veins Of Abdomen

PORTAL VENOUS SYSTEM:

· Takes blood from the entire abdomen and dumps it into the liver for processing ------> out the Suprahepatic Inferior Vena Cava.

· Abdominal venous drainage ends in the hepatic sinusoids in the liver.

· Approx 67% of the liver's blood is venous blood from the portal vein. The other 33% comes from the hepatic arteries.

· BLOOD IN THE LIVER:

§ Venous Blood Going into the liver: portal vein branches to left portal vein and right portal vein, to go to the respective functional lobes of the liver. Then it further subdivides until it gets to the hepatic sinusoids.

§ Venous blood leaving the liver: Central Vein à Sublobar Veins à Left and right Hepatic Veins àInferior Vena Cava.

· Tributaries

· Blood going to the portal vein: The anastomose of the splenic vein and superior mesenteric vein.

· Inferior Mesenteric Vein: Joins with the Splenic Vein, 60% of the time, and with the Superior Mesenteric Vein, 40% of the time.

· RELATIONS

· Right at the anastomoses of SMV and Splenic Vein, the portal vein passes posterior to the neck of the pancreas. (CLINICAL) Hence tumors in the head and neck of the pancreas can occlude the portal vein.

· Passes posterior to the common hepatic artery, just south of the liver.

· PORTAL TRIAD: Portal Vein, Proper Hepatic Artery, and Common Bile Duct, going through the Porta Hepatis on the posterior side of the liver, between the caudate and quadrate lobes.

· PORTAL HYPERTENSION: Increased blood flow in hepatic portal system, creating increased pressure in the rest of the venous system.

· Occlusion can be prehepatic, intrahepatic, or posthepatic, depending on where the occlusion occurs.

· THE PORTAL VENUS SYSTEM DOES NOT HAVE VALVES.

· Because the portal system has no valves, the blood can flow back on itself, causing an increase in pressure.

· Blood tries to get back to the heart and winds up taking collateral channels, which creates dilation outside the portal system, causing varicose veins. (This is only one cause of varicose veins).

· CAPUT MEDUSAE: Varicosity of the paraumbilical veins, due to severe portal hypertension. They look like somewhat like small snakes on the skin. They radiate in a wheel-like fashion.

· Ascites: Increased fluid in the peritoneal cavity. Can result from the liver's inability to handle increased blood pressure.

· Hemorrhoids: Varicose veins in the anal regions.

· COUGH UP BLOOD: Blood backflow into esophageal plexus could make you cough up (or vomit) blood from portal hypertension. Important clinical diagnostic sign.

· COLLATERAL VENOUS PATHWAYS: In the event of portal hypertension or portal stenosis.

· Paraumbilical Pathway: The paraumbilical vein feeds into the portal vein, in the left lobe the liver.

o These are usually closed off after birth, but in the event of portal hypertension, they can recanalize.

· Umbilical Veins (recanalized) à Inferior Epigastric Veins à Superficial Epigastric Veins -----> IVA / SVC.

· Esophageal Pathway: Blood back flows into the left gastric and eventually makes its way back to the azygos vein.

o Left Gastric Vein à Esophageal Vein (plexus)à Inferior Thyroid Veins (one on each side) à Azygos system of veins

· Caval/Portal Pathway: At the pectinate line is another collateral pathway.

o Upper portion of anal canal drains via Superior Rectal Vein à IMV

o Lower Portion of anal canal drains via MIddle and Inferior Rectal Veins à Caval System.

· PECTINATE LINE: The two venous systems anastomose with each other, so backflow can take the alternative route at that location.

· HEMORRHOIDS:

o INTERNAL HEMORRHOIDS: Hemorrhoids in the upper anal canal caused by varicosities of the superior rectal vein. They are innervated by autonomic nerves and hence are not painful.

o EXTERNAL HEMORRHOIDS: Varicosities of the inferior and middle rectal veins. They are innervated by somatic nerves and are painful.

Category: Anatomy Notes