12 November 2010 Cardiovascular Physiology Today’s lecture: MAP and TPR Blood Vessels Lab next week: Human Electrocardiography and Blood Pressure

1QQ # 27 for 8:30 am During isovolumetric contraction of the left ventricle a) the mitral valve is open b) the aortic valve is closed c) pressure in the left ventricle is greater than in the left atrium d) pressure in the left ventricle is greater than in the aorta e) the pressure is rising very rapidly in the left ventricle. Acting via beta-adrenergic receptors, EPI will Increase heart rate Increase stroke volume Increase ejection fraction Increase the rate of tension development in cardiac myofibers Increase twitch duration in cardiac myofibers.

1QQ # 27 for 9:30 am During isovolumetric relaxation of the left ventricle a) the mitral valve is open b) the aortic valve is closed c) pressure in the left ventricle is greater than in the left atrium d) pressure in the left ventricle is greater than in the aorta e) the pressure is rising very rapidly in the left ventricle. Acting via muscarinic AChRs, acetylcholine will Decrease heart rate Increase stroke volume Increase ejection fraction Increase the rate of tension development in cardiac myofibers Increase twitch duration in cardiac myofibers.

CO = HR x SV 5L/min = 72 beat/min x 70 ml/beat 35L/min =. beat/min x CO = HR x SV 5L/min = 72 beat/min x 70 ml/beat 35L/min = ? beat/min x ? ml/beat S 1 So far, we’ve dealt with the factors that control Cardiac Output by changing heart rate and stroke volume.

Summary of Factors that Regulate Cardiac Output Fig. 12.28 Even persons with heart transplants can adjust CO in the absence of innervation of heart. 12.28.jpg Notice: No Parasymp innervation of Cardiac Myofibers, Parasymp to Conducting Cells only.

Heart is pump that generates pressure gradient. Blood flows through vessels, which have resistance. Arterioles have greatest resistance and create “backpressure” in the arteries and aorta. Mean Arterial Pressure = diastolic +1/3(systolic – diastolic) = 70 + 1/3(120-70) = 70 + 17 = 87 mm Hg

Mean Arterial Pressure = Cardiac Output x Total Peripheral Resistance MAP = CO x TPR MAP = (HR x SV) x TPR

Properties of Blood Vessels All vessels and heart chambers lined with ENDOTHELIAL cells (simple squamous) Arteries Arterioles Capillaries Venules Veins Elastic, low compliance, large diameter, low resistance vessels Resistance vessels Exchange Wall = simple squamous endothelium Capacitance vessels, high compliance, low pressure, valves for unidirectional flow

Fig. 12.29 S 6 Aorta Brachial or Femoral artery Damage to artery vs vein Pusatile flow 12.29.jpg

6 S 7 Fig. 12.39b Analogy: river width and flow 12.39b.jpg

S 8 Fig. 12.30 Elastic recoil of stretched arterial walls during ventricular systole maintains arterial pressure during diastole as blood drains into arterioles. Atherosclerosis 12.30.jpg Point of Confusion: Smooth muscles in arterial walls DO NOT rhythmically contract!

Arteries and Arterial Pressure Mean Arterial Pressure Arteriole Arterioles have two main functions: 1) regulate flow to tissues and organs and 2) responsible for Total Peripheral Resistance which influences Blood Pressure. MAP = CO x TPR Poiseulle’s Equation

S 10 Fig. 12.50 12.50.jpg

S 11 Receptors for other ligands Alpha receptors more common except in skeletal muscle arterioles which have more B2 receptors