Portal System: Overview

00:01 Now, let's turn our attention to the portal system within the abdomen.

00:05 And specifically, how venous blood passes from the gastrointestinal tract utilizing the accessory organs of digestion, specifically the liver and passes back into the renal system of the body.

00:19 So let's have a look at venous drainage and the portal system in the abdomen.

00:23 So here, just to kind of describe very schematically what this means.

00:27 We have the heart, which is obviously passing arterial blood to the entire system, and then returning from the various aspects of the body.

00:35 So here we've got the kidneys, but it could be anywhere.

00:37 It could be muscle bellies, it could be the brain, it could be the head, and neck, the lungs, etc, etc.

00:42 The arterial system takes blood to those.

00:45 And then the venous system returns it back towards the heart to be pumped around the body.

00:50 The arterial system also passes towards the stomach where blood is then taken from the stomach via this portal venous system where it passes to the liver.

01:00 So once the food has been ingested and absorbed by the stomach and both the small intestines, that nutrient rich blood then has to pass through the liver before it can then go back into the normal general circulation throughout the body.

01:15 And here we have a special system called the portal venous system.

01:19 And this means that all the ingested food as is entered into the bloodstream then enters this portal venous system.

01:27 That takes blood through the liver.

01:29 So essentially, it can be processed and made safe before it then goes back into normal circulation.

01:36 Things like deamination take place in the liver.

01:39 That means essentially, amino groups are removed from various parts of the ingested food.

01:44 But it's an important process that means blood can then return to the natural circulatory system to then pass around the rest of the body.

01:54 So let's have a look as we have done in all of these videos.

01:56 The general layout and the anatomy of these structures.

02:01 So here we can see we have the stomach, the spleen, parts of the pancreas and the duodenum.

02:06 Let's start looking at the portal system and its main components.

02:10 Here we have the portal vein.

02:12 You can see how the portal vein is situated posterior to the stomach, and it's formed from the splenic vein passing from the spleen.

02:21 Remember, this is running posterior to the pancreas.

02:25 You can also see the portal vein has been formed by the superior mesenteric vein.

02:31 That follows a similar path to the superior mesenteric artery and they run together.

02:36 So they run anterior to the horizontal, the third part of the duodenum.

02:40 And then, they pass deep posteriorly to the neck of the pancreas.

02:45 You can see then that the portal vein is formed from the splenic vein and the superior mesenteric vein, pretty much covering the foreguts and the midgut.

02:55 Venous drainage from the hindgut is why the inferior mesenteric vein and classically you will see this draining into the splenic vein.

03:03 But as you'll see later on, there can be some variation within this.

03:07 So here we have the formation of the portal vein.

03:10 Once the portal vein is then passing via the gastroduodenal ligament within the free edge of the lesser omentum, it passes towards the liver where it splits into left and right branches, and these paths to the left and right functional lobes of the liver.

03:28 So we can see the portal vein giving rise to the portal system as it passes towards the liver, taking all of the venous blood from the gastrointestinal tract.

03:40 This allows that blood to pass through the liver before it goes back into general circulation.

03:47 So let's have a look at some of the anatomy and the relations of these blood vessels, specifically the portal vein, splenic vein, superior mesenteric and inferior mesenteric veins.

03:58 We can see here that the portal vein is lying posterior to the superior parts of the duodenum.

04:03 We can see here adding the lesser omentum.

04:06 And we can see it running alongside the bile duct and the hepatic artery proper.

04:10 And remember those organs, those vessels are running within the portal triad.

04:16 Running along the free edge of the lesser omentum, as they go to or from in case of the bile duct, the liver.