BIOL 320 1 st Edition Lecture 9 Outline of Last Lecture I Cardiac Cycle II Cardiac Output Flow Chart to Increase Cardiac Output III Regulation of Stroke Volume SV Three Factors that Regulate SV IV Effects of Calcium in Cardiac Muscle V Heart Development VI Congenital Heart Defects VII Aging of the Heart I II III Blood Vessels Structure Arteries Capillary Beds sites of gas exchange Thoroughfare channel bypass capillary bed Outline of Current Lecture IV Capillary Modifications V Venules Veins VI Hemodynamics VII Blood Flow Long Term Auto regulation of Blood Flow Blood Flow Skeletal Muscles Blood Flow Brain VIII Blood Pressure IX Venous Return X Blood Pressure Regulation Cardiac Output Regulation by BP Short Term BP Controls VMC Regulation Baroreceptor Reflex Long Term BP Regulation Renal Current Lecture Capillary Modifications Continuous Capillaries o Structure endothelial tissue wrapped around exterior tight junctions tight intra cellular clefts that allow diffusion blood brain barrier o Located skin muscle Sinusoids o Structure loose and leaky large intra cellular cleft cell solutes etc can pass through easily o Located liver bone marrow spleen Fenestrations o Structure portholes windows or pores present intermediate leakiness between the three types solutes and chemicals can pass through pores o Located near endocrine glands kidney small intestine Venules Veins Have valves anti backflow valves Veins have a large diameter thin walled are low pressure with high volume tubes and hold the most blood at any point in time throughout the body What do varicose veins and hemorrhoids have in common o Both have damage to these anti backflow valves Vascular anastomoses a cross connection between other vascular tubes o Brain heart abdominal organs joints Hemodynamics Blood flow volume of blood through a define area Blood pressure force exerted on vessel wall Resistance peripheral resistance opposition to flow highest in arterioles Resistance factors most important factor in blood flow o Viscosity changes with hydration o Blood Vessel Length o Blood Vessel Diameter changes most frequently Blood Flow Blood flow through entire CVS cardiac output CO At rest relatively constant Blood flow in individual organs varies with need Flow is directly proportional to change in pressure greater the difference the faster the flow Poiseuille s Law o Inversely proportional to resistance Inversely proportional to viscosity Inversely proportional to vessel length Directly proportional to vessel diameter o Directly proportional to pressure Regulation of Blood Flow o Intrinsic mechanisms auto regulation distribute blood flow to individual organs and tissues as needed Metabolic Controls Decrease o pH dilates o O2 dilates Increase o CO2 dilates o K dilates o Prostaglandins dilates o Adenosine dilates o Nitric oxide dilates o Endothelins constricts Myogenic Controls Increase o Stretch contricts o Extrinsic mechanisms maintain mean arterial pressure MAP redistribute blood during exercise and thermoregulation Nerves Sympathetic constricts Hormones Epinephrine Norepinephrine o receptors constricts o receptors dilates Angiotensin II constricts Antidiuretic hormone ADH constricts Atrial natriuretic peptide ANP dilates Long Term Auto regulation of Blood Flow o Angiogenesis growing of new blood vessels Occurs when short term auto regulatory can t meet tissue needs Increase number of vessels to region existing vessels enlarge Blood Flow Skeletal Muscles o At rest myogenic general neural mechanisms predominate o During muscle activity Blood flow increase relative to tissue activity Local controls over ride sympathetic vasoconstriction o Muscle blood flow can increase 10x or more during physical activity Blood Flow Brain Blood Pressure Pulse pressure PP SP Systolic pressure DP Diastolic pressure MAP DP 1 3PP MAP Mean Arterial Pressure pressure that propels blood to target Biggest pressure difference occurs in the arterioles since they spread the blood out disperse to capillary beds Venous Return Allowed by these factors o Respiratory pump o Muscular pump o Valves anti backflow These help increase EDV get the heart more full Blood Pressure Regulation Why bother o Maintains flow through capillary beds o To change regional blood flow based on needs o Counteract gravity Factors o Cardiac Output CO o Peripheral Resistance vasoconstriction vasodilation dehydration o Blood volume regulation via kidneys Cardiac Output Regulation by BP o Normal HR control P ANS CIC SV stroke volume control venous return EDV o Under Stress HR control S ANS CAC SV stroke volume control Epinephrine neural regulation increase contractility SV decrease ESV Venous return increase due to increased activity muscle respiratory pumps Short Term BP Controls o Neural controls Specific demands Overcome pooling in legs when suddenly stand after sitting for a while Direct blood to active areas muscles skin Recover pressure lost with hemorrhage Maintenance of MAP via altering blood vessel diameter Operate via reflex arcs Receptor baroreceptors Integration center vasomotor center Effector smooth muscle on outside of vessels arteries arterioles o Vasomotor center cluster of S ANS neurons in medulla never an on off always maintains constant low level of activity to be ready o Cardiovascular center Vasomotor center CAC CIC o S ANS activity increase vasoconstriction increase BP o S ANS activity decrease P ANS takes over decrease BP o Vasomotor center regulation Chemoreceptor Reflex Location aorta carotid artery Measure oxygen and carbon dioxide Stimuli low oxygen or elevated carbon dioxide Action activate VMCenter Result vasoconstriction speed blood back to heart Coupled with increased HR VMC Regulation Baroreceptor Reflex o High BP Increase CIC Vasodilation S ANS decrease HR contractility CO o Low BP VMC stimulate vasoconstriction Increase CAC decrease CIC S ANS increase HR and contractility CO Long Term BP Regulation Renal o Control mechanism via blood volume o Direct Pathway with time baroreceptors can adapt to chronic high low BP o Result High BP kidneys eliminate water decrease BP Low BP kidneys keep water increase BP o Indirect Pathway when BP low leads to vasoconstriction enhances renal reabsorption Renin Angiotensin mechanism o High blood pressure medications diuretics eliminate water decrease blood volume