Intro to the Cardiovascular System - Vasculature I (Jahn).pdf

Intro to the Cardiovascular System – Vasculature I Stephan C. Jahn, Ph.D. General Anatomy of Blood Vessels Copyright © The McGraw-Hill Education. Permission required for reproduction or display....

Intro to the Cardiovascular System – Vasculature I Stephan C. Jahn, Ph.D. General Anatomy of Blood Vessels Copyright © The McGraw-Hill Education. Permission required for reproduction or display. Capillaries Artery: Tunica interna Tunica media Tunica externa Nerve Vein Figure 20.1a (a) © The McGraw-Hill Companies, Inc./Dennis Strete, photographer 1 mm Arteries carry blood away from heart Veins carry blood back to heart 20-2 The Vessel Wall 20-3 Figure 20.2 Blood Vessel Structure and Function There are five types of blood vessels:  Arteries Carry blood from the heart to tissues Consist of endothelium, smooth muscle  Arterioles Carry blood from arteries to capillaries  Capillaries Connect arterioles to venules Very small Where nutrient exchange happens  Venules Start collecting blood to go back to the heart Similar to arterioles  Veins Main pathway back to the heart Similar to arteries Aided by the skeletal muscle pump, and breathing (the respiratory pump)  Arteries Arteries are classified by size  Conducting (elastic or large) arteries Biggest arteries Aorta is an example Have a layer of elastic tissue, internal elastic lamina, at the border between interna and media External elastic lamina at the border between media and externa Expand during systole, recoil during diastole  Expansion takes pressure off smaller downstream vessels  Recoil maintains pressure during relaxation and keeps blood flowing 20-5 Arteries  Distributing (muscular or medium) arteries Distributes blood to specific organs Brachial, femoral, renal, and splenic arteries Smooth muscle layers constitute three-fourths of wall thickness  Resistance (small) arteries Arterioles: smallest arteries  Control amount of blood to various organs Thicker tunica media in proportion to their lumen than large arteries and very little tunica externa 20-6  Capillaries Capillaries—site where gasses, nutrients, wastes, and hormones pass between the blood and tissue fluid  Composed of endothelium and basal lamina  Absent or scarce in tendons, ligaments, epithelia, cornea, and lens of the eye 20-7  Capillary Beds Capillary beds are networks of 10-100 capillaries  Usually supplied by a single arteriole  At distal end, capillaries transition to venules  At any given time, three-fourths of body’s capillaries are shut down Within the capillary bed, precapillary sphincters control flow  When sphincters are relaxed, capillaries are well perfused with blood  When sphincters contract, they constrict the entry to the capillary and blood bypasses the capillary 20-8 Capillary Beds 20-9 Veins Greater capacity for blood containment than arteries Thinner walls, flaccid, less muscular and elastic tissue Collapse when empty, expand easily Have steady blood flow Merge to form larger veins Subjected to relatively low blood pressure  Averages 10 mm Hg with little fluctuation 20-10  Veins Postcapillary venules—smallest veins  Even more porous than capillaries so also exchange fluid with surrounding tissues  Tunica interna with a few fibroblasts and no muscle fibers  Most leukocytes emigrate from the bloodstream through venule walls 20-11  Veins Muscular venules—up to 1 mm in diameter  One or 2 layers of smooth muscle in tunica media  Have a thin tunica externa Medium veins—up to 10 mm in diameter  Thin tunica media and thick tunica externa  Tunica interna forms venous valves  Varicose veins result in part from the failure of these valves  Skeletal muscle pump propels venous blood back toward the heart 20-12  Veins Large veins—diameter larger than 10 mm  Some smooth muscle in all three tunics  Thin tunica media with moderate amount of smooth muscle  Tunica externa is thickest layer Contains longitudinal bundles of smooth muscle  Venae cavae, pulmonary veins, internal jugular veins, and renal veins 20-13  Circulatory Routes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Simplest and most common route for (a) Simplest pathway (1 capillary bed) blood (b) Portal system Heart arteries (2 capillary beds)  arterioles (c) Arteriovenous anastomosis (shunt) capillaries venules veins  Passes through only (d) Venous (e) Arterial anastomoses anastomoses Figure 20.9 one network of capillaries 20-14