Blood vessel between the blood and the tissues; and the veins, which carry blood from the capillaries back toward the heart. The word "vascular", meaning relating to the blood vessels, is derived from the Latin "vas", meaning vessel. A few structures (such as cartilage and the lens of the eye) do not contain blood vessels and are labeled. The arteries and veins have three layers. The middle layer is thicker in the arteries than it is in the veins: Capillaries consist of little more than a layer of endothelium and occasional connective tissue. When blood vessels connect to form a region of
Mesenteric arteries smaller mesenteric vessels, the resistance of blood flow to the gut increases, and hence blood flows more readily to other organs. Mesenteric arteries The mesenteric arteries take blood from the aorta and distribute it to a large portion of the gastrointestinal tract. Both the superior and inferior mesenteric arteries arise from the abdominal aorta. Each of these arteries travel through the mesentery, within which they branch several times before reaching the gut. In humans, many of these branches are named, but in smaller animals the branches are more variable. In some animals, including humans, branches of these arteries join with