Portocaval Anastomosis - WikiLectures
The circulatory system functions to deliver oxygen, nutrients, and hormones to all the red) carry highly oxygenated blood back to the heart so it can enter the systemic circulation. hepatic portal system is injected with yellow latex in your rats. Reflect the heart towards the head to see how the cranial vena cavas meet the. A portacaval anastomosis is a specific type of anastomosis that occurs between the veins of the portal circulation and those of the systemic circulation. 2. more generally, any part of the systemic circulation in which blood draining from the capillary bed of one structure flows through a larger vessel(s) to supply.
So what's the first thing that kind of comes across?
Well, blood leaves the right ventricle, goes through a valve. And after, on the other side, you've got this area right here. And I've drawn it as one tube with no split, and this is the pulmonary trunk. So blood is headed towards the lungs, going first through the trunk. And of course, after the trunk there's a left and right.
So I'll write that up here. The pulmonary arteries are next.
And remember, I call them arteries because they're going away from the heart. And there are two arteries. So pulmonary arteries, left and right pulmonary arteries. And that's why you see two things here. One here, and you see one here. And those are basically tubes. So it's going from the pulmonary trunk.
It's splitting into one of the two tubes. And now I'm drawing the left and right lung up top. And of course, you know that the lungs are actually not going to look this way. So this is not anatomically correct.
But this is not, as I said in the beginning, a bad way of thinking about it. So blood goes through the lungs and then comes out on the other side.
And there we're going to talk about left and right pulmonary veins. And actually, here I'm going to make the point that there aren't just two pulmonary veins, one for each lung. Actually, there are usually more than that.
Two circulations in the body (video) | Khan Academy
And so when I draw this, too, I really want you to just think of the two sides, veins coming from both sides. But the actual number could be a few pulmonary veins in total. The pulmonary veins drain blood, then, into the left atrium, right? So now we're on the other side of the heart. And for the moment, I'm going to kind of pause the journey here. So we've gone from the right ventricle, around to the lungs, back again in the left atrium.
And this is kind of the first part of our journey. And this part of the journey is called the pulmonary circulation. I'm actually just going to write that here. So the fact that this part is going-- starting from the heart and going back to the heart is one circuit, and our heart actually has two circuits.
But I want to point out the circuits one at a time, and we've already kind of completed one circuit. So I'm going to take some blue paint to indicate deoxygenated blood, or blood without oxygen. I'm going to paint in how it would look. And actually, it stopped there because my arrows. But you can actually see now the deoxygenated blood kind of goes from the right ventricle, through the pulmonary trunk, through the arteries, and into the left and right lung.
And once it's there, it's going to kind of mix in with the capillaries. And it's going to start getting oxygen, and then it's going to come out on the other side in the pulmonary veins.
And it's again stopped a little bit there, but I can fill it in. And the pulmonary veins are going to deliver that oxygenated blood to the left atrium. So what you see kind of colored in now is the pulmonary circulation. That's the first part of our circuit. But let's now keep going and now talk about the second part of the circulatory system, which is the systemic circulation.
So now the journey starts with the left ventricle, so let me start there. So for the systemic circulation, I'm going to start the left ventricle. And it's going to go around to the body, right? The body is kind of the thing that's going to be receiving all of the blood. And when I say body, I really mean lots of things.
I mean things like the brain, so it could be an organ like the brain or the liver. It could also be maybe things like bones, if you have bones in your fingers. Could be the toes. Could be any part of your body that you can think of, right? So all these different organs and tissues are going to be getting blood from the left ventricle.
It's going to be going initially through a giant vessel. This vessel I'm going to label it say, here, as the aorta. So this large vessel is the aorta. And of course, it branches and splits. And I haven't shown all the branches that come off the aorta. But there are many, many of them. It goes to the various tissues and organs, and then it comes back out on the other side.
And at the end, kind of somewhere up here, it's going to go back to the right atrium. And it generally travels through two major kind of vessels. One is the inferior, and the other is the superior, meaning lower and upper. And they're both called vena cava.
So superior vena cava and inferior vena cava. I'll just write that here. So these are the two major veins that are bringing back blood from all the different parts of the body. And so now you've actually seen the second circulation, because it all ends at the right atrium.
And this is the systemic circulation. I'm going to write systemic circulation here. So now you can see that the heart is really two different systems-- or let's say two different circuits, rather.
And the first one, the pulmonary circulation, is really kind of relying on the right ventricle as the pump. And the second one is relying on the left ventricle as the pump. And actually, now that you've seen it, I can now color it in.
There it would kind of deliver all the blood to the various organs, and then the organs would use up the oxygen. So let me show it kind of now going back to blue just to indicate deoxygenated blood, and it goes back to the right atrium as deoxygenated blood. So this is kind of how we sometimes see it. For example, nitroglycerin cannot be swallowed because the liver would deactivate the medication, but it can be taken under the tongue or transdermally through the skin and thus is absorbed in a way that bypasses the portal venous system.
Inversely, dextromethorphana cough suppressor, is best taken orally because it needs to be metabolised by the liver into dextrorphan in order to be effective.
| CK Foundation
This latter principle is that of most prodrugs. The use of suppositories is a way to bypass partially the portal vein: Blood flow to the liver is unique in that it receives both oxygenated and partially deoxygenated blood.
As a result, the partial gas pressure of oxygen pO2 and perfusion pressure of portal blood are lower than in other organs of the body. Blood passes from branches of the portal vein through cavities between "plates" of hepatocytes called sinusoids.
Blood also flows from branches of the hepatic artery and mixes in the sinusoids to supply the hepatocytes with oxygen. This mixture percolates through the sinusoids and collects in a central vein which drains into the hepatic vein. The hepatic vein subsequently drains into the inferior vena cava. The rest comes from the partially deoxygenated blood from the portal vein.