EXSS 376 1st Edition Exam 2 Study Guide Cardiovascular System Overview Three major circulatory elements o Pump heart o Channels or tubes blood vessels o Fluid medium blood Heart generates pressure to drive blood through vessels Blood flow must meet metabolic demands Structure Heart is a dual pump containing 4 chambers 2 upper chambers atria o Receive blood from blood vessels returning blood to the heart veins 2 lower chambers ventricles o Eject blood from heart into blood vessels arteries Note left ventricle more hypertrophied than right because it pumps blood through the entire body Valves 2 valves situated between the atria and ventricles AV valves o right tricuspid left bicuspid 2 valves guard blood flow from ventricles semilunar valves o aortic left and pulmonary right Heart Layers Wall has 3 distinct layers o Epicardium outer layer Formed with visceral pericardium o Myocardium middle layer Composed of cardiac tissue what makes heart pump 95 of heart layer cardiac muscle fibers are interconnected by intercalated discs to form a functional syncytia mechanically and electrically interconnected cells acting as 1 unit 2 cell junctions are present in an intercalated disc desmosome binds sarcolemmas together mechanical gap junction allow action potentials to move from 1 cardiac muscle cell to another electrical o Endocardium inner layer Provides smooth lining for the chambers of the heart and covers the valves of the heart Cardiac Conduction System Sinoatrial SA node pacemaker of the heart initiates action potentials o Located on right atrial wall o On its own SA would fire AP s every 0 6 sec 100 per min with parasympathetic tone 75 per min If you took the heart out of the body would beat at 100 bpm o Causes atria to contract Action potential reaches atrioventricular AV node o Action potential slows down o Provides time for blood to enter ventricles From AV nodes AP enters bundle of his AP travels down right and left bundle branches Purkinje fibers rapidly conduct the AP throughout ventricles o Ventricles contract Cardiac Cycle Cardiac cycle all events associated with 1 contraction Can be divided into 3 phases o Relaxation period all 4 chambers in diastole o Atrial systole atria contract o Ventricular systole ventricles contract 1 Relaxation Period o end of cardiac cycle when all 4 chambers in diastole relaxed o what happens in atria Blood flows into relaxed atria o What happens in ventricles Ventricles relax Pressure drops in ventricles Semilunar valves close When ventricular pressure drops below atrial pressure ventricles begin to fill Accounts for 75 of ventricular filling o majority of blood entering ventricles occurs during relaxation period 2 Atrial Systole o atrial contraction forces remaining blood 25 in atria into relaxed ventricles tricuspid and bicuspid valves open 3 Ventricle Systole o at first ventricular contraction pushes tricuspid and bicuspid vales closed prevents back flow increased pressure closes valves o ventricular pressure increases and then open semilunar valves o blood is ejected to aorta and pulmonary arteries Cardiac Output CO volume of blood pumped by each ventricle per min L min At rest 5 L min Cardiac output at rest does not change 2 determinates HR bpm and SV volume of blood pumped per beat typical values o predicted HR max 220 age o at rest trained vs untrained same cardiac output trained lower HR but higher SV o at max exercise max HR is same but trained has higher SV higher Q cardiac output Stroke Volume SV EDV ESV o EDV End Diastolic Volume Amount of blood in the ventricle at the END of diastole right before it contracts o ESV End Systolic Volume Amount of blood in ventricle at end of SYSTOLE what is left over after contraction Cardiac Output Control Heart rate o Parasympathetic activity rest digest Increasing PARASYMPATHETIC activity will DECREASE HR Resting threshold starts LOWER o Sympathetic activity fight or flight Increasing SYMPATHETIC activity will INCREASE HR Threshold is reached more RAPIDLY Stroke volume o Sympathetic activity Increased force of contraction less blood left over lower ESV Squeezes more blood out of the chamber o EDV venous return EDV length of cardiac muscle fibers Frank starling mechanism greater the stretch greater subsequent contraction strength of contraction EDV stretches cardiac fibers SV Vascular System arteries carry blood away from heart arterioles control blood flow feed capillaries capillaries site of nutrient and waste exchange venules collect blood from capillaries veins carry blood from venules back to heart Blood Pressure force per unit area that blood places on the inside of the wall of a blood vessel mmHg primary cardiovascular variable being regulated is MEAN ARTERIAL PRESSURE o ensures adequate BLOOD FLOW to tissues systolic highest pressure in artery during systole top number diastolic lowest pressure in artery during diastole bottom number MAP average blood pressure in arteries o Diastolic 1 3 systolic diastolic BP systolic diastolic No blood flow going through when at 140 slowly release hear tapping initial sound blood intermittently going through vessel keep releasing it until hear nothing diastolic flowing freely w out constriction Pressure greatest near the heart just enough in veins to bring back to heart Pressure force that drives flow Determinants of MAP 1 Total peripheral resistance TPR o resistance in peripheries 2 Blood Volume o decrease blood volume decrease blood pressure o minor decrease in blood volume has only minimal effect on BP o 10 blood loss decreases BP o water retention may increase blood volume and INCREASE BP 3 Cardiac Output o any increase in CO or Q will increase MAP IF TPR remains constant Total Peripheral Resistance TPR opposition to blood flow due to FRICTION between blood and walls of the blood vessels Depends on o Vessel radius MOST IMPORTANT Decrease in diameter increases resistance to blood flow Influenced by Local tissue metabolic controls o Increase O2 vasoconstrictor because already meeting O2 needs o Increase CO2 H vasodilator indicates exercise more byproducts made need more blood flow less resistance o Increase Nitric oxide vasodilator smoking influences ability to dilate Sympathetic activity fight flight o Increase SYMP activity vasoconstrictor o Vessel length o Blood viscosity Resistance length viscosity radius 4 Blood Increase viscosity increase amount of formed elements RBC OR decrease water plasma Hematocrit RBC in total blood volume 45 formed elements 55