Cardiovascular Physiology 14

Structure of the Heart The heart valves ensure one-way flow Figure 14-7g

Heart Valves PLAY Animation: Cardiovascular System: Anatomy Review: The Heart Figure 14-9

Heart Valves

Histology of Myocardium Involuntary muscle Striated, has sarcomeres Many mitochondria Uni- or binucleated Branched Intercalated Disc Rhythmic contractions Does not fatigue as easily as skeletal Does not have individual neuromuscular junctions Independent contractions Require high O2

Cardiac Muscle versus Skeletal Muscle Smaller and have single nucleus per fiber Have intercalated disks Desmosomes allow force to be transferred Gap Junctions provide electrical connection T-tubules are larger and branch Sarcoplasmic reticulum is smaller Mitochondria occupy one-third of cell volume

Excitation-contraction coupling and relaxation in cardiac muscle Sarcoplasmic reticulum (SR) ECF ICF T-tubule Ca2+ spark Ca2+ signal SR Ryanodine receptor-channel Ca2+ ions bind to troponin to initiate contraction. Voltage-gated Ca2+ channels open. Ca2+ enters cell. Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). Local release causes Ca2+ spark. Action potential enters from adjacent cell. Summed Ca2+ Sparks create a Ca2+ signal. 1 2 3 4 5 6 Figure 14-11, steps 1–6

Excitation-contraction coupling and relaxation in cardiac muscle Myosin Relaxation Contraction ATP Sarcoplasmic reticulum (SR) ECF ICF Actin T-tubule Ca2+ spark Ca2+ signal SR Ryanodine receptor-channel stores Ca2+ ions bind to troponin to initiate contraction. Relaxation occurs when Ca2+ unbinds from troponin. Voltage-gated Ca2+ channels open. Ca2+ enters cell. Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). Local release causes Ca2+ spark. Ca2+ is pumped back into the sarcoplasmic reticulum for storage. Action potential enters from adjacent cell. Summed Ca2+ Sparks create a Ca2+ signal. 1 2 3 4 5 6 8 7 Figure 14-11, steps 1–8

Excitation-contraction coupling and relaxation in cardiac muscle Myosin Relaxation Contraction ATP 3 Na+ 2 K+ Sarcoplasmic reticulum (SR) ECF ICF Actin T-tubule Ca2+ spark Ca2+ signal SR Ryanodine receptor-channel stores Ca2+ ions bind to troponin to initiate contraction. Relaxation occurs when Ca2+ unbinds from troponin. Na+ gradient is maintained by the Na+-K+-ATPase. Voltage-gated Ca2+ channels open. Ca2+ enters cell. Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). Local release causes Ca2+ spark. Ca2+ is pumped back into the sarcoplasmic reticulum for storage. Ca2+ is exchanged with Na+. Action potential enters from adjacent cell. Summed Ca2+ Sparks create a Ca2+ signal. 1 2 3 4 5 6 9 10 8 7 Figure 14-11, steps 1–10

Myocardial Contractile Cells Action potential of a cardiac contractile cell Phase Membrane channels PX = Permeability to ion X +20 -20 -40 -60 -80 -100 Membrane potential (mV) 100 200 300 Time (msec) PK and PCa PNa Na+ channels open Na+ channels close Ca2+ channels open; fast K+ channels close Ca2+ channels close; slow K+ channels open Resting potential 1 2 3 4 Resting membrane potential is -90mv. Na+ passes through double gated voltage channels Plateau results from decreased K+ and increased Ca++ Plateau end when flux is reversed Figure 14-13

Myocardial Contractile Cells Refractory periods and summation in skeletal and cardiac muscle- this prevents summation as it happens in skeletal muscle Figure 14-14c

Modulation of Heart Rate by the Nervous System Sympathetic stimulation targets If channels to open rapidly. Parasympathetic stimuation targets K+ and Ca++ channels, it hyper-polarizes the cell and slows depolarization Figure 14-16

Electrical Conduction in Myocardial Cells 1% of myocardial cells are designed to spontaneously generate an action potential. They can contract without outside signal= autorhythmic. Pacemaker cells do not have sarcomeres Figure 14-17

Electrical Conduction in Heart THE CONDUCTING SYSTEM OF THE HEART SA node AV node Purkinje fibers Bundle branches A-V bundle Internodal pathways SA node depolarizes. Electrical activity goes rapidly to AV node via internodal pathways. Depolarization spreads more slowly across atria. Conduction slows through AV node. Depolarization moves rapidly through ventricular conducting system to the apex of the heart. Depolarization wave spreads upward from the apex. 1 4 5 3 2 Purple shading in steps 2–5 represents depolarization. Figure 14-18

Electrical Conduction & Einthoven’s Triangle AV node Direction of electrical signals Delay the transmission of action potentials SA node Set the pace of the heartbeat at 70 bpm AV node (50 bpm) and Purkinje fibers (25-40 bpm) can act as pacemakers under some conditions

Electrical Activity Comparison of an ECG and a myocardial action potential Figure 14-22

The Electrocardiogram ECG give info on heart rate, heart rhythm, conduction velocity, and heart condition. Three major waves: P wave, QRS complex, and T wave Waves correspond to events of the cardiac cycle. Figure 14-20

Electrical Activity Correlation between an ECG and electrical events in the heart P wave: atrial depolarization P START Atria contract. PQ or PR segment: conduction through AV node and A-V bundle Q Q wave R wave R S wave QS ELECTRICAL EVENTS OF THE CARDIAC CYCLE Repolarization ST segment Ventricles contract. S The end T wave: ventricular T Figure 14-21

Electrical Activity The P wave reflects the activity of the atria. The atria contract from top to bottom so the P-wave ends after full atrial depolarization P wave: atrial depolarization START Atria contract. PQ or PR segment: conduction through AV node and A-V bundle P ELECTRICAL EVENTS OF THE CARDIAC CYCLE Figure 14-21 (2 of 9)

Electrical Activity The P-Q segment reflects the flow of current along the interventricular septum via the AV node and AV bundle. This is the time when the ventricles are relaxed and filling with blood P wave: atrial depolarization START Atria contract. PQ or PR segment: conduction through AV node and A-V bundle P Q Q wave ELECTRICAL EVENTS OF THE CARDIAC CYCLE Figure 14-21 (3 of 9)

Electrical Activity The QRS complex occurs while the ventricles contraction (depolarize) from the apex & upwards. At the end of the contraction all blood volume to be expelled as been pushed out. S-T segment happens during ventricular repolarization (relax) P wave: atrial depolarization START Atria contract. PQ or PR segment: conduction through AV node and A-V bundle P Q Q wave R wave R S wave QS ELECTRICAL EVENTS OF THE CARDIAC CYCLE ST segment Ventricles contract. S Figure 14-21 (6 of 9)

Electrical Activity The T-wave indicates ventricular repolarization- meaning that the muscle is coming back to a resting state. At this point the chambers are ready to receive blood P wave: atrial depolarization START P The end R PQ or PR segment: conduction through AV node and A-V bundle P T QS P Atria contract. T wave: ventricular Repolarization Repolarization ELECTRICAL EVENTS OF THE CARDIAC CYCLE R P T QS P Q wave Q ST segment R R wave P R Q S P Ventricles contract. R Q P S wave QS Figure 14-21 (9 of 9)

Electrical Activity Normal and abnormal electrocardiograms Figure 14-23

Mechanical Events Mechanical events of the cardiac cycle PLAY START Late diastole: both sets of chambers are relaxed and ventricles fill passively. Atrial systole: atrial contraction forces a small amount of additional blood into ventricles. Isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. relaxation: as ventricles relax, pressure in ventricles falls, blood flows back into cups of semilunar valves and snaps them closed. Ventricular ejection: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected. 5 4 1 2 3 PLAY Animation: Cardiovascular System: Cardiac Cycle Figure 14-24

Mechanical Events Figure 14-24, steps 1–2 Late diastole: both sets of START 1 2 Late diastole: both sets of chambers are relaxed and ventricles fill passively. Atrial systole: atrial contraction forces a small amount of additional blood into ventricles. Figure 14-24, steps 1–2

Mechanical Events Figure 14-24, steps 1–3 1 START 1 2 3 Late diastole: both sets of chambers are relaxed and ventricles fill passively. Atrial systole: atrial contraction forces a small amount of additional blood into ventricles. Isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. Figure 14-24, steps 1–3

Mechanical Events Figure 14-24, steps 1–4 1 START 4 1 2 3 Late diastole: both sets of chambers are relaxed and ventricles fill passively. Atrial systole: atrial contraction forces a small amount of additional blood into ventricles. Isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. Ventricular ejection: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected. Figure 14-24, steps 1–4

Mechanical Events Figure 14-24, steps 1–5 1 START 5 4 1 2 3 Late diastole: both sets of chambers are relaxed and ventricles fill passively. Atrial systole: atrial contraction forces a small amount of additional blood into ventricles. Isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. relaxation: as ventricles relax, pressure in ventricles falls, blood flows back into cups of semilunar valves and snaps them closed. Ventricular ejection: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected. Figure 14-24, steps 1–5

Cardiac Cycle Left ventricular pressure-volume changes during one cardiac cycle A B C 65 100 135 Left ventricular volume (mL) 120 80 40 EDV ESV D Stroke volume KEY EDV = End-diastolic volume ESV = End-systolic volume One cardiac cycle Left ventricular pressure (mm Hg) Figure 14-25

Cardiac Cycle At the beginning of the diastolic phase the ventricles are relax and contain a very small amount of blood A 65 100 135 Left ventricular volume (mL) 120 80 40 KEY EDV = End-diastolic volume ESV = End-systolic volume Left ventricular pressure (mm Hg) Figure 14-25 (1 of 4)

Cardiac Cycle At then of the diastolic phase the volume as increased because the ventricle has filled after the ventricles contracted A B 65 100 135 Left ventricular volume (mL) 120 80 40 EDV KEY EDV = End-diastolic volume ESV = End-systolic volume Left ventricular pressure (mm Hg) Figure 14-25 (2 of 4)

Cardiac Cycle At point C (systole phase) the pressure has increased but the volume has not changed A B C 65 100 135 Left ventricular volume (mL) 120 80 40 Left ventricular pressure (mm Hg) EDV KEY EDV = End-diastolic volume ESV = End-systolic volume Figure 14-25 (3 of 4)

Cardiac Cycle At the end of systole the pressure is at is highest and the volume has dropped. Stroke volume= EDV - ESV A B C 65 100 135 Left ventricular volume (mL) 120 80 40 EDV ESV D Stroke volume KEY EDV = End-diastolic volume ESV = End-systolic volume One cardiac cycle Left ventricular pressure (mm Hg) Figure 14-25 (4 of 4)

Wiggers Diagram This diagram shows the relationship between the cardiac cycle, the ECG, the heart sounds, and pressure changes in the left ventricle and aorta Electro- cardiogram (ECG) Pressure (mm Hg) Heart sounds Left ventricular volume (mL) Dicrotic notch P Cardiac cycle Atrial systole Ventricular diastole T S2 S1 Atrial systole Early Late Isovolumic contraction pressure Left atrial 65 135 30 60 90 120 Time (msec) 100 200 300 400 500 600 700 800 Aorta QRS complex Figure 14-26

Wiggers Diagram This shows the correlation between the carciac cycle and the ECG. Notice between the T wave of one and P wave of another the ventricles are relaxed while the atria are filling and beginning to empty prior to atrial depolarization Electro- cardiogram (ECG) P Cardiac cycle Atrial systole Ventricular diastole T Atrial systole Time (msec) 100 200 300 400 500 600 700 800 Early ventricular Late Isovolumic contraction QRS complex Figure 14-26

Wiggers Diagram Left ventricular volume (mL) Atrial systole Ventricular diastole Atrial systole 65 135 Time (msec) 100 200 300 400 500 600 700 800 Early Late Isovolumic contraction This phase shows the changes in blood volume as the ventricle contracts (depolarizes) or relaxes (repolarizes) Figure 14-26

Wiggers Diagram You can see the relationship between pressure chages in teh atrium and the cardiac cycle. Notice that the lowest atrial pressure is during ventricular diastole. Pressure (mm Hg) Left ventricular volume (mL) Atrial systole Ventricular diastole Atrial systole Left atrial pressure 65 135 30 60 90 Time (msec) 100 200 300 400 500 600 700 800 Early Late Isovolumic contraction Figure 14-26

Wiggers Diagram This shows changes in ventricular pressure and valve sounds as the AV valve (S1) and semilunar valves (S2) close. Pressure (mm Hg) Heart sounds Atrial systole Ventricular diastole S2 S1 Atrial systole Left ventricular pressure 135 30 60 90 120 Time (msec) 100 200 300 400 500 600 700 800 Early Late Isovolumic contraction Figure 14-26

Wiggers Diagram This shows changes in ventricular pressure and ventricular blood volume. Pressure (mm Hg) Left ventricular volume (mL) Atrial systole Ventricular diastole S2 S1 Atrial systole pressure 65 135 30 60 90 Time (msec) 100 200 300 400 500 600 700 800 Early Late Isovolumic contraction Figure 14-26

Wiggers Diagram The top line shows changes in pressure of the aorta as the left ventricle contracts or relaxes. The dicrotic notch occurs as a sharp drop in pressure results from a drop in blood flow once the ventricle begins to relax Pressure (mm Hg) Heart sounds Dicrotic notch Atrial systole Ventricular diastole S2 S1 Atrial systole Left ventricular pressure 30 60 90 120 Aorta Time (msec) 100 200 300 400 500 600 700 800 Early Late Isovolumic contraction Figure 14-26

Wiggers Diagram Figure 14-26 Pressure (mm Hg) Heart sounds Dicrotic notch Atrial systole Ventricular diastole S2 S1 Atrial systole Left ventricular pressure Left atrial 30 60 90 120 Aorta Time (msec) 100 200 300 400 500 600 700 800 Early Late Isovolumic contraction Figure 14-26

Wiggers Diagram Electro- cardiogram (ECG) Pressure (mm Hg) Heart sounds Left ventricular volume (mL) P Atrial systole Ventricular T S1 pressure Left atrial 65 135 30 60 90 120 Time (msec) 100 200 300 Aorta QRS complex This shows all the events that are happening during one complete ECG wave Figure 14-26

This shows all the changes happening during ventricular diastole Wiggers Diagram Electro- cardiogram (ECG) Pressure (mm Hg) Heart sounds Left ventricular volume (mL) Dicrotic notch P Cardiac cycle Atrial systole Ventricular diastole T S2 S1 pressure Left atrial 65 135 30 60 90 120 Time (msec) 100 200 300 400 500 600 700 800 Aorta Late QRS complex This shows all the changes happening during ventricular diastole Figure 14-26

These are all the events during one complete cardiac cycle Wiggers Diagram Electro- cardiogram (ECG) Pressure (mm Hg) Heart sounds Left ventricular volume (mL) Dicrotic notch P Cardiac cycle Atrial systole Ventricular diastole T S2 S1 Atrial systole pressure Left atrial 65 135 30 60 90 120 Time (msec) 100 200 300 400 500 600 700 800 Aorta Early Late Isovolumic contraction QRS complex These are all the events during one complete cardiac cycle Figure 14-26