Discuss the different types of blood vessels and how their structure is uniquely suited to their functions?

Although all the blood vessels of the body are actually
one continuous system, anatomists generally divide them into three functional
categories: Arteries, veins, and capillaries.

Arteries and
veins are both composed of three major layers, or tunics. The outer
layer is the tunica adventitia, which is a fibrous protective layer with a lot of
collagen. The tunica media, or middle layer, is composed of elastic connective tissue
and smooth muscle. The innermost layer, or tunica intima, is primarily elastic tissue
with a lining of endothelial cells.

The major difference
between arteries and veins is the thickness of the layers. In arteries, all the layers
are thicker and more robust than in veins, with the exception of the endothelial lining.
Arteries are subjected to the full pressure of the heart, so they need to be more
elastic to maintain shape, and they need more muscle to help control blood flow to
various areas. Veins are under much less pressure so they tend to be less elastic, but
veins have valves, which are extra flaps of endothelium, to help keep blood from flowing
backwards in response to gravity in between heart
beats.

Capillaries are composed of only a single layer of
tunica intima. This makes them very thin, which allows gasses and other materials to be
exchanged between the blood and body cells easily. Because of their simple structure,
capillaries are both prone to damage and easy to repair. Their tiny diameter allows them
to have a large surface area in contact with body cells.