UNIT 3 Blood Vessels Part 1 of 2

1. UNIT 3 Blood Vessels Part 1 of 2 Structure and Function of Arteries, Veins, and Capillaries Blood Volume Distribution Factors Affecting Blood Pressure (7th edition)

2. What to read for Unit 3: Chapter 19, pp. 714-742, of your textbook; pp. 742-767 will be covered in Unit 4 of this course (7th edition)

3. Overview of Blood Vessels ARTERIES - take blood away from the heart ARTERIOLES - small arteries VEINS - carry blood toward the heart VENULES - small veins CAPILLARIES - site of gas exchange (7th edition)

4. Basic Structure of Arteries, Veins, and Capillaries (fig. 19.1, table 19.1) Arteries - thicker walled and smaller lumen than veins; are exposed to the highest blood pressures; composed of three layers (tunics): tunica intima � composed of simple squamous epithelium (endothelium); it is the innermost layer to the lumen (blood-filled space); the smooth endothelium provides a low friction contact with blood. tunica media � middle layer; this layer is very thick in arteries; contains sheets of smooth muscle, which can contract and relax, thereby changing the blood vessel diameter: vasoconstriction - contraction of the smooth muscle to make the vessel lumen smaller; under the control of the ANS vasodilation - relaxation of the smooth muscle to make the vessel lumen larger; under the control of the ANS elastic arteries - have a large amount of elastin in the tunica media which allows them to expand and recoil muscular arteries - have a large amount of smooth muscle in the tunica media which allows them to constrict and dilate tunica externa (=tunica adventitia) � composed of connective tissue; outermost layer (7th edition)

5. Basic Structure of Arteries, Veins, and Capillaries (fig. 19.1, table 19.1) Veins - thinner walled and larger lumen than arteries which allows them to hold large volumes of blood; these vessels experience the least pressure as they are farthest from the heart; composed of three layers (tunics): tunica intima � composed of simple squamous epithelium (endothelium); it is the innermost layer to the lumen (blood-filled space) tunica media � middle layer; contains sheets of smooth muscle, but less than arteries tunica externa (=tunica adventitia) � composed of connective tissue; outermost layer; this is the predominant layer of the vein wall Capillaries - smallest of the blood vessels; very thin walled; composed of only a lumen and tunica intima (endothelium) only; no smooth muscle; capillaries are where the exchange of materials takes place between blood and tissues (7th edition)

6. Arterial System (table 19.1; fig. 19.2a) ELASTIC (Conducting) Arteries - the arteries closest to the heart as blood leaves the heart it is under the most pressure the first arteries that the blood goes through must stretch to absorb the pressure; when the heart relaxes, they recoil to propel the blood forward the elastin within the wall of the elastic fibers allows them to expand and recoil the AORTA and other elastic arteries experience the widest variation in pressure, and thus must have the ability to accommodate those pressure changes MUSCULAR (Distributing) Arteries - the arteries further from the heart and under less pressure these arteries contain a large amount of smooth muscle in their tunica media the contraction of the smooth muscle causes a constriction of the artery, thus decreasing the blood vessel diameter and the amount of blood that passes through the relaxation of the smooth muscle causes a dilation of the artery, thus increasing the blood vessel diameter and the amount of blood that passes through 4. vasomotor nerves of the sympathetic nervous system synapse with the smooth muscle and regulate blood vessel diameter (7th edition)

7. Arterial System (table 19.1; fig. 19.2a) Arterioles - the smallest arteries the largest arterioles have all three layers (tunics) in common with arteries and veins the blood pressure is less in arterioles than in the muscular arteries; the biggest pressure drop occurs in the arterioles (fig. 19.5) (7th edition)