Chapter 14 Cardiovascular System Blood Vessels and Blood Pressure Autonomic Control of the Heart Intrinsic Control of the Heart Starling s Law When the rate at which blood ows into the heart from the veins venous return changes the heart automa cally adjusts its output to match the in ow In chapter 13 we saw that cardiac output is regulated both extrinsically autonomic nervous system controlling heart rate and stroke volume as well as intrinsically regulaFon of stroke volume In chapter 14 we will also see that the vasculature is also regulated intrinsically and extrinsically Vasculature Flow Change in Pressure resistance Overview of Vasculature Blood vessels are classi ed according to whether they carry blood to or away from the heart and according to size Arteries and smaller arterioles carry blood from the heart and to capillaries Venules and then larger veins return blood back to the heart Overview of Vasculature The lumen of all blood vessels is lined by a layer of epithelial cells called endothelium The walls of all blood vessels except capillaries contain various amounts of smooth muscle Within the connecFve Fssue are collagen and elasFn proteins enabling them to withstand large pressures and expand and contract Arteries One of the major funcFons of arteries is as a pressure reservoir to ensure a con nual smooth ow of blood even when the heart is not pumping diastole During systole arterial walls expand due to increased volume stretching the elasFn like a spring During diastole when no more blood is entering the arteries the elasFn recoils passively propelling blood forward The average arterial pressure during the cardiac cycle is the mean arterial pressure MAP When you go to a physician to have your blood pressure taken what is actually measured is an esFmate of the arterial pressure Blood Pressure To measure blood pressure the technician increases cu pressure above the systolic arterial pressure causing the artery to collapse and stop blood ow The valve slowly lets air out and the pressure drops unFl the vessel can open causing blood to ow through in a turbulent fashion which can be heard through the stethoscope systolic arterial pressure Once the pressure drops just below the diastolic pressure Korotko sounds disappear diastolic arterial pressure Hypertension elevated mean arterial pressure 1 in 3 adults 70 million Americans Hypertension is closely associated with atherosclerosis or hardening of the arteries In atherosclerosis a fa y plaque builds up in the walls of arteries decreasing its elas city and narrowing the lumen increasing resistance Hypertension also damages the walls of the arteries predisposing them for atherosclerosis Also increases the likelihood of myocardial infarcFon Overview of Vasculature The smallest arteries branch into even smaller arterioles which can lead into a capillary bed Arterioles provide the greatest resistance to blood ow but their resistance can also be regulated Resistance is regulated both intrinsically and extrinsically by the contracFon and relaxaFon of smooth muscle Arterioloes and Resistance to Blood Flow When arteriolar smooth muscle contracFon increases the radius of the arterioles decreases vasoconstric on and resistance increases When the arteriolar smooth muscle relaxes the radius of arterioles increases vasodila on and resistance decreases Intrinsic Control of Blood Flow Distributed to Organs Vascular smooth muscle cells in arterioles are sensiFve to in the extracellular uid and respond to changes in concentraFons of a wide variety of substances These changes in concentraFon occur as a result of metabolic ac vity RegulaFon in Response to Metabolic AcFvity Changes associated with increased metabolic acFvity generally cause vasodila on whereas changes associated with decreased metabolic acFvity induce vasoconstric on Extrinsic Control of Arteriole Radius The sympatheFc nervous system innervates the smooth muscle of most arterioles During periods of increased sympatheFc acFvity norepinephrine binds to adrenergic receptors and acFvates second messengers to result in vasoconstricFon Extrinsic Control of Arteriole Radius In addiFon the release of epinephrine secreted by the adrenal medulla can also bind to adrenergic receptors causing vasoconstric on Hoormonal Control of Arteriole Radius Vasopressin secreted by the posterior pituitary and angiotension II also promote vasoconstricFon thereby increasing the MAP Summary of Extrinsic Control of Arteriole Radius