The circulatory system includes both the blood vascular system and the lymph vascular system. The blood vascular system includes the heart, arteries, arterioles, capillaries, venules, and veins. It is organized into two circuits: (1) the pulmonary circuit and (2) the systematic circuit. The right half of the heart pumps blood into the pulmonary circuit via the pulmonary artery to the lungs and back to the heart via the pulmonary vein. The left heart then pumps the oxygenated blood into the systematic circuit via the Aorta. In the systemic capillaries oxygen and nutrients leave the blood and waste materials (i.e. CO2) picked up and returned to the heart.
In general, three types of arteries are found in the body: (1) Elastic Arteries, (2) Muscular Arteries, and (3) Arterioles. All three types are composed of three coats or tunics: (1) tunica intima (inner most), (2) tunica media (middle), and (3) adventitia (outer most).
Muscular arteries (Muscular Artery 1) consist of a tunica intima composed of an inner endothelial lining sitting on an elastic lamina. The tunica media, the thickest layer, is composed of spiral smooth muscle cells held together by elastic fibers and an encircling elastic lamina. The tunica adventitia is composed of fibroelastic connective tissue, with much of its elastic component contributing to the make up of the elastic lamina surrounding the media. This layer can be as thick as to 2/3 of that of the media (Muscular Artery 2).
Elastic arteries (Elastic Artery 1) possess a much thicker intima, a thick media with an increased amount of elastic fibers arranged in concentric laminae, and adventitia similar to the muscular artery, except being much thinner (Elastic Artery 2).
The Aterioles contain the same three tunicas, but each is greatly reduced. The intima consist of an endothelium on a basement lamina; the media contains only three layers of smooth muscle cells; and the adventitia thin (Arteriole).
Capillaries are the thinnest walled of all the blood vessels and represent the site of gas and nutrient exchange in the systemic circulatory system. A capillary is composed of endothelial cells, surrounded by a basement membrane (Capillaries).
Veins (Vein1) and the smaller venules are composed of three tunica: the intima, media and adventitia. The intima is composed of endothelial cells, resting on a poorly defined elastic lamina. The media is very thin and is composed of some circular smooth muscle (not continuous) and mostly collagen. The adventitia is the thickest tunica and is composed of collagenous connective tissue (Vein 2). Since these vessels carry oxygen poor blood, the media and adventitia are supplied with a separate vascular system. These vessels are called the vaso vasorum and are also found in the walls of large arteries (Vaso vasorum).
See if you can identify the following blood vessels and their component parts:
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