Vasculature - Venous Drainage of the Abdomen Flashcards
What are the two venous systems that drain the abdominal structures?
1) Portal venous system - drains blood to the liver for processing
2) Systemic venous system - drains blood to the right atrium of the heart.
Systemic venous system?
What is the major vein involved in this system?
The major vessel in this system is the inferior vena cava.
Inferior vena cava?
The IVC is the common convergence of venous drainage from all structures below the diaphragm. It is located on the posterior abdominal wall; anteriorly to the vertebral column and to the right of the abdominal aorta.
The vessel is formed by the union of the common iliac veins at the L5 vertebral level. It ascends superiorly, and leaves the abdomen by piercing the central tendon of the diaphragm at the T8 level (at the caval hiatus). Within the thorax, the IVC drains into the right atrium of the heart.
During its long course, the IVC shares the anatomical relationship with numerous abdominal structures - including the right common iliac artery, the root of the mesentery, the head of the pancreas, the bile duct, the portal vein and the liver.
Tributaries of the IVC?
The IVC is responsible for drainage of all structures below the diaphragm. It receives tributaries from:
1) Common iliac arteries - formed by the external and internal iliac veins. they drain the lower limbs and the gluteal region.
2) Lumbar veins - drain the posterior abdominal wall.
3) Renal veins - drains the kidneys, left adrenal gland, and the left testis/ovary.
4) Right testicular/ovarian vein - drain the right testes or ovary respectively in men and women.
5) Right suprarenal vein - drains the right adrenal gland (the left adrenal vein drains into left renal vein).
6) Inferior phrenic veins - drains the diaphragm.
7) Hepatic veins - drains the liver.
There are no tributaries from the spleen, pancreas, gall bladder or the abdominal part of the GI tract - as these structures are first drained into the portal venous system. However, venous return from these structures ultimately enters the IVC via the hepatic vein (after being processed by the liver.
Portal venous system?
The portal system carries venous blood (rich in nutrients that have been extracted from food) to the liver for processing.
The major vessel of the portal system is the portal vein. It is the point of convergence for the venous drainage of the spleen, pancreas and, gall bladder and the abdominal part of the GI tract. The portal vein is formed by the splenic vein and the superior mesenteric vein, posterior to the neck of the pancreas at the level of L2.
As it ascends towards the liver, the portal vein passes posteriorly to the superior part of the duodenum and the bile duct. Immediately before entering the liver, the portal vein divides into right and left branches which then enter the parenchyma of the liver separately.
Tributaries of the hepatic portal vein?
It is formed by the splenic and SMV. It receives additional tributaies from:
1) Right and left gastric veins - drain the stomach.
2) Cystic veins - drains the gallbladder.
3) Para-umbilical veins - drain the skin of the umbilical region.
Splenic vein?
It is formed by a variety of smaller vessels as they leave the hilum of the spleen.
Unlike the splenic artery, the splenic vein is straight and it maintains contact with the body of the pancreas as it crosses the posterior abdominal wall. As it reaches the neck of the pancreas, the splenic vein joins the superior mesenteric vein to form the portal vein.
Tributaries of the splenic vein?
1) Short gastric veins - drains the fundus of the stomach
2) Left gastro-omental veins - drains the greater curvature of the stomach.
3) Pancreatic veins - drain the pancreas.
4) Inferior mesenteric vein - drains the colon.
The inferior mesenteric vein drains the blood from the rectum, sigmoid colon, descending colon and splenic. It begins as the superior rectal vein and ascends, receiving tributaries from the sigmoid veins and the left colic veins. As it ascends further it passes posteriorly to the body of pancreas and typically joins the splenic vein.
Superior mesenteric vein?
The superior mesenteric vein drains blood from the small intestine, cecum, ascending colon, and transverse colon. It begins in the right iliac fossa, as a convergence of the veins draining the terminal ileum, cecum and appendix. It ascends within the mesentery of the small intestine, and the travels posteriorly to the neck of the pancreas to join the splenic vein.
Tributaries of the SMV?
1) Right gastro-omental vein - drain the greater curvature of the stomach.
2) Anterior and posterior inferior pancreaticoduodenal veins - drain the pancreas and duodenum.
3) Jejunal vein - drain the jejunum.
4) Ileal vein - drain the ileum.
5) Ileocolic vein - drains the ileum, colon and cecum.
6) Right colic vein - drains the ascending colon.
7) Middle colic vein - drains the transverse colon.
Clinical relevance - porto-systemic anastomoses?
This is a connection between the veins of the portal venous system, and the veins of the systemic venous system. The major sites of these anastomoses include:
1) Oesophageal - between the oesophageal branch of the left gastric vein and the oesophageal tributaries to the azygous system.
2) Rectal - between the superior rectal vein and the inferior rectal vein.
3) Retroperitoneal - between the portal tributaries of the mesenteric veins and retroperitoneal veins.
4) Paraumbilical - between the portal veins of the liver and the veins of the anterior abdominal wall.
When blood flow through the portal system is obstructed (e.g. due to cirrhosis, portal vein thrombosis, or external pressure from a tumour), the pressure within the portal system increases. A portal venous pressure in excess of 20mmHg is defined as portal hypertension.
In portal hypertension, blood may be re-directed through the porto-systemic anastomoses (as these are now under a lower pressure). If a large volume of blood passes thorugh these anastomoses over a long period of time, the veins around the anastomosis can become abnormally dilated - known as varices. Rupture of oesophageal or rectal varices can result in fatal blood loss.
