Let's talk about the hepatic portal system. So, to do that, we've got to discuss normal circulation. So, the heart is going to pump blood out of arteries, and those arteries then branch and give rise to arterioles, which then give rise to capillaries, where gas exchange occurs and fluid exchange occurs between the capillaries and the interstitium.
Venules leave the capillaries, and those venules then become into veins, and the veins go back into the heart, and the circulation begins again. Hepatic portal system is a wee bit different. where the heart is going to pump blood out of arteries, and those arteries are going to then branch into arterioles, which then gives rise to capillaries. This is the first capillary. These are the capillaries that are lining the lamina propria of the small and large intestines.
Then the venules drain those capillaries that give rise to veins, and these are veins of the hepatic portal system. And then those veins become venules again, and they dump into a second capillary bed, capillary bed number two. These are the hepatic sinusoids, and we looked at these in the histology lab, which then give rise to venules.
We call those venules the terminal hepatic venules, which then dump into veins, such as the hepatic veins and into the inferior vena cava, and back to the heart. And so, there's one, then two capillary beds in a series. That's what makes a portal system unique. Here's normal and hepatic circulations, one capillary in the series.
two capillaries in the series. So what are these veins? This is one of my illustrations of the hepatic portal system. And to orient ourselves, there is the liver. And then in purple, there's the esophagus, which then dumps into the stomach.
And then there is the spleen. Pancreas is not illustrated in other organs or the gallbladder. But there's the small intestines, the jejunum and ileum is what's being represented there.
And then that's the beginning of of the large intestine, there's the ascending colon, and you can see the appendix along the bottom, and then there's the hindgut, the part of the transverse colon, descending colon, sigmoid colon, and rectum. And in blue, there's the hepatic portal vein. I'm calling it hepatic portal vein so that you get an idea of where this is located, hepatic for liver, but most of the times, people just call it the portal vein. And that portal vein then dumps into the parenchyma of the liver, And then blood flows through those sinusoids to be collected by these hepatic veins.
And those hepatic veins drain into the inferior vena cava and go back to the heart. So let's go back to this portal vein. Now the portal vein collects GI visceral blood. So all the blood from the gut tube, foregut, midgut, hindgut, and accessory digestive glands and the spleen.
So foregut is going to drain, midgut, and hindgut. So... let's talk about the foregut, shall we?
So the foregut is made up of distal esophagus, the stomach, first and second part of the duodenum, liver and gallbladder, pancreas and spleen. And so the way that veins that drain in from the foregut include our gastric veins, left and right gastric veins that drain from the lesser curvature of the stomach directly into the portal vein. And then we have our gastro-omental veins that drain both to the portal vein and to the splenic vein, both.
And another word for the gastro-mental vein is the gastro-epiploic. They're synonymous. Then we have our splenic vein, that as its name implies, is going to drain blood from the spleen, but also hugging that splenic vein that's not illustrated is the pancreas.
And the pancreas has numerous veins, the pancreatic veins, that go from the pancreas into the splenic. So next we have our midgut. And from the midgut, we've...
is comprised of the duodenum, second, third, and fourth part, jejunum, ilium, and then cecum and appendix, ascending colon, and part of the transverse colon. Though on this illustration, all we see is part of the small intestine, appendix, cecum, and part of the ascending colon. The superior mesenteric vein is what drains the midgut and all those organs of the midgut. So all veins from the superior, well, of the midgut end up in the superior mesenteric vein. which has the tributaries of the superior mesenteric vein, have the same name and distribution as the arteries.
So the hindgut is comprised of the transverse colon, descending colon, sigmoid colon, and the rectum. And so the portal vein is going to drain that hindgut and all those organs via the inferior mesenteric vein, draining all of those, and then the inferior mesenteric vein drains into the splenic, which then goes into the hepatic portal vein. portal vein into the liver. And the tributaries of the inferior mesenteric vein have the same name and distribution as the arteries. All right, easy breezy.
So, a couple of things about the hepatic portal system. One, hepatic portal system lacks valves, and as a result, blood flow can be in any direction depending on pressure gradient. Keep that in mind. Let's talk about portocaval anastomosis. What are those?
Well, there are three primary tissue areas in the GI tract, and in the belly, I should say, where blood drains to both hepatic portal system and the cavil veins. And those three primary tissue areas are the distal esophagus, the rectum, and the superficial abdomen. So let's talk about those three portocaval anastomosis with the following illustrations.
Now, this illustration, let's orient ourselves. There's the liver, and there's the distal esophagus and the stomach, and there's the umbilicus. There's the rectum and purple down to the bottom. And just for orientation, that's the descending colon or part of the descending colon.
All right. So some other things. That's our inferior vena cava where we can see right, that would be the area at the bottom of the diaphragm.
And that inferior vena cava goes down and then bifurcates to the common iliac vein and then gives rise to an internal iliac vein and an external iliac vein. Now that we have this orientation and we know that There's the portal vein draining into the liver. Let's take each of these three portal cavulonastomosis and talk about them. First with the esophagus. So the distal esophagus drains both portally and cavally.
So let's talk about the portal drainage first. There's the distal esophagus and that left gastric vein drains blood from the distal esophagus and the left gastric vein goes to the hepatic portal vein, which then drains into the liver, goes through the sinusoids, hepatic veins. inferior vena cava back to the heart.
But the distal esophagus also has caval drainage, where we take this distal esophagus and some of the blood also drains through these esophageal veins that go directly to the azagus veins, which then go into the superior vena cava. So the distal esophagus has both portal and caval drainage at that junction. So why do we care about this?
What's so significant? What can potentially happen when there's congestion in the portal vein? So, let's say that cirrhosis of the liver, let's say that that's a blood clot. Regardless of what it is, we now have blood that's congested in the hepatic portal vein and it becomes into high pressure, we call it portal hypertension.
And that X that just dropped represents that blockage. That circle of red represents flowing of blood. And if there's a blockage and blood keeps building up, blood starts flowing backwards. And blood then starts coursing down all these tributaries, splenic vein, supermesenteric vein, and this left gastric vein, and gets to this distal esophagus.
But blood just flows where it's pushed. And because blood can do that, and there's no valves in the hepatic portal system, blood reaches this distal esophagus. And guess what happens? The blood keeps getting pushed through those esophageal veins into the azagus system of veins.
which begs the question, what do you think happens to those esophageal veins? The answer, esophageal varices, where that yellow is showing that area where blood is then coursing from the portal to the cavell, through that portal cavell and astimoses, and those veins usually don't have that much blood, so they swell really big in that area, and here we see all those veins swelling. big and they're basically become varicose veins in the distal esophagus and they would and if burst they bleed quickly and they bleed fast and then this can end up being critical and usually fatal because they swallow the blood and then they exsanguinate. Second, rectum.
All right, so that's rectum down at the bottom. Now the rectum has portal and cable drainage. We're going to talk about portal drainage first where there's the rectum and then through the superior rectal vein goes into the inferior mesenteric vein that goes into the splenic vein, which goes to the hepatic portal vein and into the liver, portal drainage. Now let's talk about caval drainage, where in the same part of the rectum, blood can then drain through the middle and inferior rectal veins into the internal iliac vein, which then goes into the common iliac vein, which then goes into the inferior vena cava back to the heart.
So, Here we have both of those systems. What can potentially happen when there's congestion in the portal vein? Well, there's the congestion and there's the blood, and blood flows epatophugally or backwards through the portal vein to the splenic and down the splenic and it keeps getting backed up all the way down to the rectum.
And guess what? Blood says, hey, there's another vessel we can go back to the heart. So it goes through these inferior middle rectal veins to the cavil back to the heart. What do you think happens to the rectal veins?
There, they swell and they end up with internal hemorrhoids where you get these varicose veins inside the rectum and these veins get burst and they get a dilate, sometimes converse, but they dilate and giving them hemorrhoids. Finally, our anterior abdominal wall. So we have caval drainage first.
We'll talk about that. This is the primary drainage of the anterior abdominal wall, like the camper's fascia. So you've got these. superficial epigastric veins that drain all the way down to the femoral vein and the femoral vein courses deep to the inguinal ligament becoming the external iliac and then goes into the common iliac, into the inferior vena cava, and back to the heart. Well, the anterior abdominal wall, the campers fascia, also has portal drainage where we've got these peri-umbilical veins that then follow the round ligament in through the umbilicus and down that false form ligament to the liver and then into the portal vein.
So here we have the two anastomoses. So what can potentially happen where there's congestion in the portal vein? Well, we take that blood, and it then courses retrogradely through these parambilical veins into those parambilical veins around the belly button, and then continue down the superficial epigastrics to the femoral vein, and then through the common iliac up to the IVC.
What do you think happens to the parambilical veins in the superficial abdominal wall? They dilate. resulting in a condition called caput medusa, that radiating from the umbilicus or all these tiny parambilical veins.
And they're not used to having that much blood and they dilate and get really, really big. And it kind of looks like the head of medusa with all these snakes. So they call it caput medusa.
So portal cable anastomosis have three different tissue areas where blood drains from those tissues, both portally and cavally. One, distal esophagus, goes to both the azagus system, cable, and the left gastric vein to the portal vein, portal. Two, rectum.
Here, blood drains to the inferior mesenteric vein, back to the portal vein, or the lower rectal veins that go to the cavil system. And finally, three, those parambilical veins go to portal, superficial epigastric go cavally. Another way to remember these is gut, butt, and kaput.
Distal esophagus is part of the gut tube. rectums in the butt, and Kaput Medusa results because of parambilical veins. Thank you.