CHAPTER 13 BLOOD VESSELS & CIRCULATION

 Three layers  Tunica Interna: innermost layer  Tunica Media: smooth muscle  Tunica Externa: connective tissue; stabilization within tissues  Vasoconstriction: arterial contraction; diameter decreases  Vasodilation: arterial relaxation; diameter increases BLOOD VESSEL ANATOMY

 Elastic arteries: elastic fibers for stretching (high systolic pressures, i.e. aorta, pulmonary trunk)  Muscular arteries: supply blood to muscles and organs (i.e. carotid)  Arterioles: have thin tunica media ARTERIES

 Vital functions at the capillary level: chemical and gaseous exchange between the blood and interstitial fluid takes place across capillary walls  Diameter: 8 µm (~1 RBC)  Thin walls: slows blood flow for exchange; one layer of cells (no media/externa)  Capillary beds: network of capillaries; autoregulated by precapillary sphincters CAPILLARIES

 Return blood to the heart  Venules: smallest veins; <50µm lack tunica media  Medium-sized veins: 2- 9mm; has tunica media and thick tunica externa  Large veins: 2 venae cavae & 3 tributaries; thin media, thick externa  Low pressure; valves in medium veins prevent back flow and increase venous return  Damaged valves: varicose veins & hemorrhoids VEINS

 Focal Calcification: aging causes calcification of tunica media  Atherosclerosis: increased level of lipids in blood circulation can lead to formation of plaques  Treatment options: medication, surgery (angioplasty, stent, bypass), LIFESTYLE CHANGE CLINICAL NOTE: ARTERIOSCLEROSIS ch?NR=1&v=MGzyhuCs43o &feature=fvwp v=S9AqBd4RExk

 Pressure: force against vessel walls; direct correlation; inc. pressure  inc. blood flow  Arterial (blood pressure)  Capillary  Venous  Resistance: oppositional force; inverse correlation; inc. resistance  dec. blood flow  Vascular: friction of walls  Viscosity: fluidity of blood  Turbulence: disruption in smooth blood flow FACTORS AFFECTING BLOOD FLOW

 Arterial:  Normal BP: 120/80  Systolic: ventricular systole (120 mmHg)  Diastolic: end of ventricular diastole (80 mmHg)  Pressure decrease from aorta to arterioles (120  30)  Capillary: (Fig. 13-7)  Arterial end (high P)  Venous end (low P)  Diffusion, filtration, and osmosis drive exchange  Venous:  Low pressure compared to arterial flow  Must overcome gravity  Muscle compressions and respiratory increase venous return CARDIOVASCULAR PRESSURES