The blood vessels are part of the circulatory system and function to transport blood throughout the body.
The most important types, arteries and veins, carry blood away from or towards the heart, respectively.
All blood vessels have the same basic structure.
The inner lining is the endothelium and is surrounded by subendothelial connective tissue.
Around this there is a layer of vascular smooth muscle, which is highly developed in arteries.
Finally, there is a further layer of connective tissue known as the adventitia, which contains nerves that supply the muscular layer, as well as nutrient capillaries in the larger blood vessels.