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What is a vein?

Definition, anatomy and function of a vein.

Show transcript

Hey there! It’s Matt from Kenhub and, on this video tutorial, I will quickly describe, what is a vein? First thing you need to know is that there are three main types of vessels that transport nutrients through the body – the arteries, the veins, and the capillaries. The image on the screen shows you some of the most important veins in your body which are all these blue structures. Here is one of the most well-known, the inferior vena cava.

Veins carry blood away from the tissues and towards the heart and have thin walls. Their internal lumen is larger than that of the arteries due to the fact that they contain blood under low pressure. They also have valves that prevent the blood from flowing backwards.

Blood that returns to the heart via the veins comes from the capillaries. They are the point where the arteries and veins merge with one another and serve as a complex plexus of many tiny branches. This is also where the exchange of gases, nutrients and waste products takes place because the capillary walls are thin and fenestrated. After they are emptied of oxygen and nutrients, the capillaries collect into venules, and finally into the veins which wind their way back to the heart.

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