Veins – Thoracic Vessels

00:01 Now, that we covered the arterial branching system to the thorax and the viscera, let’s shift our attention to the veins that I want you to understand. Those will include our pulmonary veins, our superior vena cava, the first posterior intercostal veins. Then we have an azygos system of veins. We also have our brachiocephalic veins. We’ll have our veins of the vertebral column and then, we’ll also have our inferior vena cava. This slide highlights the pulmonary veins and we have four pulmonary veins: two from the right and two from the left. And so, if we take a look at our illustration, here is our left atrium. These will be the pulmonary veins coming from the right lung. We have a right superior pulmonary vein and then we have an inferior pulmonary vein. We’ll also have the same situation on the left side, where we have a left superior pulmonary vein and then a left inferior pulmonary vein and these veins are conveying blood that’s highly saturated in oxygen as the blood is coming back from the lungs to enter the left atrium and then to be pumped out into our systemic circulation. This slide demonstrates the superior vena cava. The superior vena cava is shown right here in the illustration. It’s going to be formed by the right brachiocephalic vein and the left brachiocephalic vein. The left brachiocephalic vein is longer than is the right, because it has to course across the midline, coming from the left across the midline of the body, to then join up with the right brachiocephalic vein that’s already on the right side of the midline. The brachiocephalic veins are going to drain blood from the head and neck, the brain, upper extremity through other tributaries, as well as blood from the thorax itself. And then the blood collected here from those tributaries will empty into the right atrium. The azygos vein is a part of the azygos system of veins. The azygos vein itself is shown here in the illustration, lies to the right of the midline and it has numerous tributaries. So, it will receive the right superior intercostal vein, the right posterior intercostal veins from intercostal spaces 5 through 11, the right subcostal vein. Will also receive blood from the hemiazygos vein and the accessory hemiazygos vein, right bronchial vein. Esophageal, mediastinal and pericardial veins empty into the azygos. And the azygos vein is going to be formed by the union of the right subcostal and right ascending lumbar veins. And we can see where that occurs inferiorly on the right side of our illustration. This vein is your right ascending lumbar. Here is your right subcostal and you can see that they join at this point. And then the continuation superior is the azygos vein. And the azygos vein, as we see here, will empty into the superior vena cava. So, let’s take a look at the tributaries of the azygos vein. But, before we really get into the details of those tributaries, I’m kind of treating the first posterior intercostal veins a bit differently here. These are actually tributaries of the brachiocephalic, but as you may remember from the previous slide, the azygos vein receives a tremendous amount of blood flow from the right posterior intercostals, but that does not include the first one. So, what is it about the first posterior intercostal vein and where does it go? The first posterior intercostal vein is running just inferior to rib 1 and we start to see it here posteriorly coming into view and then it’s diving behind the brachiocephalic vein on the right and then will empty into the right brachiocephalic vein on the right. The left one is coming around here and we can just see it right here and the left first posterior intercostal vein will also empty into the left brachiocephalic vein. There is variability here, so it’s not unusual to see variability in the first posterior intercostal veins with respect to what they actually empty into. The first posterior intercostal veins will drain blood from the territory supplied by its arterial counterpart.

05:43 Now, we can focus on the tributaries of the azygos vein and the first one is going to be the right superior intercostal vein. That is shown here. And we see the right superior intercostal vein emptying into the arch of the azygos and then we see the arch, then, emptying into your superior vena cava. The right superior intercostal vein is receiving blood from the 2nd, 3rd and 4th posterior intercostal veins and again, there can be some variability in this drainage territory. And it will then drain blood from the territory that’s supplied by its arterial counterparts. The right posterior intercostal and right subcostal veins also will, then, be tributaries of the azygos. We’ve already talked about the first posterior intercostal vein going into the brachiocephalic, talked about the 2nd, 3rd and 4th posterior intercostal veins emptying into the right superior intercostal vein. That means we still have posterior intercostal veins posteriorly in intercostal spaces 5 through 11. And if we take a look, we can see these other veins in these other more inferiorly located intercostal spaces and you can see that they empty into the azygos and again, the azygos will drain that blood back into the superior vena cava. We’ve already highlighted the fact that the azygos vein is formed by the union of the right subcostal vein and the right ascending lumbar and so, the right subcostal vein is also going to be a tributary. And as with the other intercostal veins, these intercostal veins and the subcostal vein as well, are draining blood from the territory supplied by their arterial counterparts.

08:03 Another tributary of the azygos vein is the hemiazygos vein. The hemiazygos vein is on the left side of the vertebral column in this illustration and we see the hemiazygos running right along here. It’s going to be formed by the left subcostal vein and the left ascending lumbar vein and the hemiazygos is going to receive blood generally from intercostal spaces 11, 10 and 9. However, there is variability here and that is shown in the illustration.

08:47 And the blood that’s drained by the posterior intercostal veins will be blood drained from what is supplied by their arterial counterparts. And then your hemiazygos, at whatever level along the vertebral column, will drain across the vertebral column into the azygos vein.

09:11 And this may be as low as vertebral level T9, or as shown here, it’s at a higher vertebral level. More superiorly on the left side, we have an accessory hemiazygos vein that will drain blood into the azygos vein that lies to the right. The accessory hemiazygos vein is shown here and it is connected or joined with the hemiazygos, which is common. The accessory hemiazygos typically will drain blood from intercostal spaces 4 through 8 and again, it’s draining blood supplied by its posterior intercostal arterial counterparts.