These are thick-walled to cope with the high pressure of the blood flowing through it. What do you call this?

An Artery (plural arteries) is a blood vessel that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pulmonary and the umbilical arteries, which carry deoxygenated blood to the organs that oxygenate it (lungs and placenta, respectively). The effective arterial blood volume is that extracellular fluid which fills the arterial system.

The arteries are part of the circulatory system, that is responsible for the delivery of oxygen and nutrients to all cells, as well as the removal of carbon dioxide and waste products, the maintenance of optimum blood pH, and the circulation of proteins and cells of the human immune system.

Arteries form part of the circulatory system that carry blood that is oxygenated after is has been pumped from the heart. Coronary arteries also aid the heart in the blood by sending oxygenated blood to the heart, allowing muscles to function. Arteries carry oxygenated blood away from the heart to the tissues, except for pulmonary arteries, which carry blood to the lungs for oxygenation (usually veins carry deoxygenated blood to the heart but the pulmonary veins carry oxygenated blood as well).