36. Portal vein, portosystemic (caval) shunts, and their medical importance.

What is the portosystemic anastomosis?

Connection between the veins of the portal venous system and the veins of the systemic venous system

What forms the portal vein?

Superior mesenteric vein and splenic vein Inferior mesenteric vein drains to splenic, but could also drain into superior mesenteric Posterior to the neck of the pancreas At level L2

Which organs drain into the Portal venous system?

Spleen Pancreas Gallbladder Abdominal part of GI tract they drain into portal venous system -- then venous return from these structures enter the IVC --> through hepatic veins

What happens in portal hypertension?

blood can be re-directed through the porto-systemic anastomosis (since they are in lower pressure) If a large volume of blood passes through these anastomosis over a long period of time, the veins around the anastomosis can become abnormally dilated = varices rupture in these varies result in severe blood loss in esophageal and rectal circumstances

Esophageal anastomosis?

esophageal branch of left gastric and esophageal tributaries to the azygos system

How does the IVC enter the diaphragm?

it leaves the abdomen by piercing the central tendon of the diaphragm at T8 level -- the caval hiatus then it enters the right atrium of the heart

What does the portal system carry?

the portal vein carries venous blood (rich in nutrients that have been extracted from food) to the liver for processing

what happens when blood flow through the portal system is obstructed?

(due to cirrhosis, portal vein thrombosis, external pressure from tumor) -- the pressure within the portal system increases Portal venous pressure that exceeds 20 mmHg is portal hypertension

What are the major sites of the portosystemic anastomosis?

1. Esophageal 2. Rectal 3. Paraumbilical (disease example: Caput Medusae) 4. Retroperitoneal

Rectal anastomosis?

Between Superior rectal vein and middle, inferior rectal veins directly and indirectly from the internal iliac a.

Retroperitoneal anastomosis?

Between portal tributaries of the mesenteric veins (left/right colic) and the retroperitoneal veins (lumbar veins --> IVC, SVC through azygos)

Inferior vena cava receives? Location?

Blood from all structures below the diaphragm -- except for the unpaired viscera of the abdomen It is in the posterior abdominal wall, anterior to the vertebral column and to the right of the abdominal aorta.

What is the portal vein a part of?

Portal triad (with proper hepatic artery and common bile duct) , in the hepatoduodenal ligament

Paraumbilical anastomosis?

Portal veins of liver and the veins of the anterior abdominal wall (thoracoepigastric or superficial epigastric) (caput medusae)

How is the IVC formed?

union of common iliac veins at L5

2 venous systems draining in the abdomen? what do they drain?

vena cava system --> paired organs in the abdomen directly to IVC portal system --> unpaired organs in the abdomen into the liver