Arteries

In the aorta and other large arteries, there are numerous layers of elastin fibers between the smooth muscle cells of the tunica

Heart and Circulation

Venous Circuit

Arterial Circuit

Tunica externa

Tunica media

Tunica interna

Endothelium

Lumen -

Tunica externa

Heart and Circulation

Venous Circuit

Arterial Circuit

Tunica externa

Tunica media

Tunica interna

Endothelium

Lumen -

Tunica externa

Tunica media Tunica interna

Valve

Precapillary Sphincter

Tunica externa

Tunica media

Tunica interna

Tunica externa Tunica media

Tunica interna

Endothelium Lumen

Precapillary sphincter

-Basement membrane -

Tunica externa

Tunica media

Tunica interna

Tunica media Tunica interna

Valve

Tunica externa Tunica media

Tunica interna

Endothelium Valve

Endothelium Lumen

Precapillary sphincter

-Basement membrane -

■ Figure 13.25 The structure of blood vessels. Notice the relative thickness and composition of the tunicas (layers) in comparable arteries and veins.

media. These large elastic arteries expand when the pressure of the blood rises as a result of the heart's contraction; they recoil, like a stretched rubber band, when the blood pressure falls during relaxation of the ventricles. This elastic recoil drives the blood during the diastolic phase—the longest phase of the cardiac cycle—when the heart is resting and not providing a driving pressure.

The small arteries and arterioles are less elastic than the larger arteries and have a thicker layer of smooth muscle for their diameters. Unlike the larger elastic arteries, therefore, the diameter of the smaller muscular arteries changes only slightly as the pressure of the blood rises and falls during the heart's pumping activity. Since arterioles and small muscular arteries have narrow lumina, they provide the greatest resistance to blood flow through the arterial system.

392 Chapter Thirteen

Blood flow

Precapillary sphincter

Metarteriole (forming arteriovenous shunt) i

Blood flow

Blood flow

Precapillary sphincter

Metarteriole (forming arteriovenous shunt) i

Blood flow

Shunting Muscle

■ Figure 13.26 The microcirculation. Metarterioles (arteriovenous anastomoses) provide a path of least resistance between arterioles and venules. Precapillary sphincter muscles regulate the flow of blood through the capillaries.

Clinical Investigation Clues

Remember that Jason's radial pulse was fast and weak.

■ What causes the pulse in the artery?

■ What does the fast and weak pulse reveal about the pumping of Jason's heart?

Small muscular arteries that are 100 |im or less in diameter branch to form smaller arterioles (20 to 30 |im in diameter). In some tissues, blood from the arterioles can enter the venules directly through arteriovenous anastomoses. In most cases, however, blood from arterioles passes into capillaries (fig. 13.26). Capillaries are the narrowest of blood vessels (7 to 10 |im in diameter). They serve as the "business end" of the circulatory system, in which exchanges of gases and nutrients between the blood and the tissues occur.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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Responses

  • jodi
    How are metarterioles shunts?
    5 years ago
  • Autumn
    How are precapillary sphincter muscles regulated?
    5 years ago
  • amelia
    Do arteries have sphincter muscles?
    5 years ago
  • ENNIO
    Which artery offers least resistance to blood flow?
    5 years ago
  • balbo
    What are arteriovenous anastomoses?
    5 years ago
  • caterina
    What is the tunica media of the arteries?
    5 years ago
  • amaranto toscani
    How are the muscular arterioles and precapillary sphincter controlled?
    4 years ago
  • alice
    Do arteries have sphincters?
    4 years ago
  • gregor
    Do arteries or veins have sphincter muscles?
    3 years ago
  • Abel
    Do veinshave sphincters?
    2 years ago

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