Vena Cava

00:01 Now, here is a large vein, the vena cava. You know it’s a vein because look at the image on the left-hand side, it has got a large lumen, but the walls collapsed. Look at the thickness of the wall relative to the lumen. Totally different to what you see in a large artery. Now, look very carefully on the right hand side, because this is a section through the wall of the vena cava. The tunica media shown here is very thin. The tunica adventitia has smooth muscle in it running longitudinal along the length of the vena cava. That’s an unusual situation. You don’t have smooth muscle in blood vessels in the tunica adventitia. But here, you’ve got it in the vena cava.

00:57 And the reason for that is because the vena cava are so important returning blood to the heart, to the right side of the heart. And that smooth muscle in the tunica adventitia helps the blood vessel, helps the vena cava elongate or shorten depending on the postural position of the individual because the vena cava lie up against the posterior wall of the body.

01:30 So that’s a very important feature of the vena cava, to have the ability to elongate and shorten when we bend or change our posture. It’s a characteristic feature of the vena cava.