There are 2 venous units that drainpipe abdominal structures – the portal venous system and the systemic venous system. The portal device transports venous blood to the liver for handling, whilst the systemic venous system returns blood to the ideal atrium of the heart.
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In this write-up, we shall consider the anatomy of these two venous units – the major vessels affiliated, their anatomical course, and their tributaries.
Systemic Venous System
The systemic venous device transports deoxygenated blood to the appropriate atrium of the heart. The significant vessel in this device is the inferior vena cava.
Inferior Vena Cava
The inferior vena cava is the widespread convergence of venous drainage from all structures listed 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 widespread iliac veins at the L5 vertebral level. It ascends superiorly, and also leaves the abdomales by piercing the main tendon of the diaphragm at the T8 level (the caval hiatus). Within the thorax, the inferior vena cava drains right into the best atrium of the heart.
Throughout its long course, the inferior vena cava shares an anatomical relationship through many abdominal frameworks – 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.
The inferior vena cava is responsible for the venous drainage of all structures below the diaphragm. It receives tributaries from:Typical iliac veins – developed by the exterior and also inner iliac veins. They drainpipe the lower limbs and also gluteal region.Lumbar veins – drain the posterior abdominal wall.Right testicular/ovarian vein – drainpipe the best testes or ovary respectively in guys and also woguys (the left testicular/ovarian vein drains right into the left renal vein).Right suprarenal vein – drains the appropriate adrenal gland (the left adrenal vein drains right into the left renal vein).
Tbelow are no tributaries from the spleen, pancreas, gallbladder or the abdominal component of the GI tract – as these frameworks are first drained into the portal venous system. However, venous rerotate from these frameworks ultimately enters the inferior vena cava by means of the hepatic veins (after being processed by the liver).
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Fig 1.0 – The inferior vena cava and also significant tributaries. Keep in mind just how the left adrenal vein and left testicular vein empty into the left renal vein.
Portal Venous System
The portal system carries venous blood (wealthy in nutrients that have been extracted from food) to the liver for processing.
The significant vessel of the portal system is the portal vein. It is the allude of convergence for the venous drainage of the spleen, pancreas, gallbladder and also the abdominal part of the gastrointestinal tract. The portal vein is created by the union of the splenic vein and also the premium mesenteric vein, posterior to the neck of the pancreas, at the level of L2.
As it ascends in the direction of the liver, the portal vein passes posteriorly to the remarkable part of the duodenum and also the bile duct. Immediately before entering the liver, the portal vein divides right into ideal and also left branches which then enter the parenchyma of the liver individually.
The portal vein is developed by the union of the splenic vein and remarkable mesenteric vein. It receives additional tributaries from:Para-umbilical veins – drain the skin of the umbilical area.
The splenic vein is created from a range of smaller vessels as they leave the hilum of the spleen.
Unlike the splenic artery, the splenic vein is right 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 premium mesenteric vein to develop the portal vein.
Tributaries to the splenic vein include:Brief gastric veins – drainpipe the fundus of the stomach.Left gastro-omental vein – drains the better curvature of the stomach.
The inferior mesenteric vein drains blood from the rectum, sigmoid colon, descending colon and splenic flexure. It begins as the remarkable rectal vein and ascends, receiving tributaries from the sigmoid veins and also the left colic veins. As it ascends even more it passes posteriorly to the body of the pancreas and also commonly joins the splenic vein.
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Fig 2 – The hepatic portal venous system.
Superior Mesenteric Vein
The exceptional mesenteric vein drains blood from the tiny intestine, cecum, ascfinishing 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 also then travels posteriorly to the neck of the pancreas to sign up with the splenic vein.
Tributaries to the premium mesenteric vein include:Right gastro-omental vein – drains the greater curvature of the stomach.Ileocolic vein – drains the ileum, colon and cecum.Right colic vein – drains the ascfinishing colon.Middle colic vein – drains the transverse colon.
Many of these tributaries are formed as an accompanying vein for each branch of the remarkable mesenteric artery.
Clinical Relevance – Porto-Systemic Anastomoses
A porto-systemic anastomosis is a connection in between the veins of the portal venous mechanism, and the veins of the systemic venous system. The significant sites of these anastomoses include:Oesophageal – Between the oesophageal branch of the left gastric vein and the oesophageal tributaries to the azygous system.Rectal – Between the remarkable rectal vein and also the inferior rectal veins.Retroperitoneal – Between the portal tributaries of the mesenteric veins and the retroperitoneal veins.Paraumbilical – Between the portal veins of the liver and the veins of the anterior abdominal wall.
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Fig 3 – Endoscopic appearance of oesophageal varices. They deserve to undergo rupture, resulting in huge quantities of blood loss.
When blood circulation via the portal mechanism is obstructed (e.g as a result of cirrhosis, portal vein thrombosis, or exterior push from a tumour), the pressure within portal system boosts. A portal venous pressure in excess of 20mmHg is identified as portal hypertension.
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In portal hyperstress and anxiety, blood may be re-directed with the porto-systemic anastomoses (as these are now under a lower pressure). If a large volume of blood passes with these anastomoses over a lengthy duration of time, the veins roughly the anastomosis have the right to come to be abcommonly dilated – known as varices. Rupture of oesophageal or rectal varices deserve to result in fatal blood loss.