Xsection of muscle8/31/2023 ![]() ![]() The walls of arteries and veins are largely composed of living cells and their products (including collagenous and elastic fibers) the cells require nourishment and produce waste. This is critical because blood flow becomes sluggish in the extremities, as a result of the lower pressure and the effects of gravity. In addition, many veins of the body, particularly those of the limbs, contain valves that assist the unidirectional flow of blood toward the heart. Their walls are considerably thinner and their lumens are correspondingly larger in diameter, allowing more blood to flow with less vessel resistance. ![]() In other words, in comparison to arteries, venules and veins withstand a much lower pressure from the blood that flows through them. (Micrograph provided by the Regents of the University of Michigan Medical School © 2012)īy the time blood has passed through capillaries and entered venules, the pressure initially exerted upon it by heart contractions has diminished. (c) A micrograph shows the relative differences in thickness. (a) Arteries and (b) veins share the same general features, but the walls of arteries are much thicker because of the higher pressure of the blood that flows through them. Together, their thicker walls and smaller diameters give arterial lumens a more rounded appearance in cross section than the lumens of veins.įigure 2. Arteries have smaller lumens than veins, a characteristic that helps to maintain the pressure of blood moving through the system. Each type of vessel has a lumen-a hollow passageway through which blood flows. Arteries and arterioles have thicker walls than veins and venules because they are closer to the heart and receive blood that is surging at a far greater pressure (Figure 2). Shared Structuresĭifferent types of blood vessels vary slightly in their structures, but they share the same general features. The arrows indicate the direction of blood flow, and the colors show the relative levels of oxygen concentration. The systemic circuit moves blood from the left side of the heart to the head and body and returns it to the right side of the heart to repeat the cycle. The pulmonary circuit moves blood from the right side of the heart to the lungs and back to the heart. Although arteries and veins differ structurally and functionally, they share certain features.įigure 1. Pulmonary veins then return freshly oxygenated blood from the lungs to the heart to be pumped back out into systemic circulation. In contrast, in the pulmonary circuit, arteries carry blood low in oxygen exclusively to the lungs for gas exchange. The blood returned to the heart through systemic veins has less oxygen, since much of the oxygen carried by the arteries has been delivered to the cells. Systemic arteries provide blood rich in oxygen to the body’s tissues. Eventually, the smallest arteries, vessels called arterioles, further branch into tiny capillaries, where nutrients and wastes are exchanged, and then combine with other vessels that exit capillaries to form venules, small blood vessels that carry blood to a vein, a larger blood vessel that returns blood to the heart.Īrteries and veins transport blood in two distinct circuits: the systemic circuit and the pulmonary circuit. An artery is a blood vessel that carries blood away from the heart, where it branches into ever-smaller vessels. Explain the structure and function of venous valves in the large veins of the extremitiesīlood is carried through the body via blood vessels.Describe the basic structure of a capillary bed, from the supplying metarteriole to the venule into which it drains.Distinguish between elastic arteries, muscular arteries, and arterioles on the basis of structure, location, and function.Compare and contrast the three tunics that make up the walls of most blood vessels.Each of the following quizzes include 15 multiple-choice questions on the muscles of a specific area of the body.By the end of this section, you will be able to: There's a lot to learn when it comes to the muscular system, including not only the location of every muscle, but also their actions, and their origins and insertions. ![]()
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