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Heart. Heart as a pump Two separate pumps –Right heart Blood to respiratory system –Left heart Blood to the peripheral organs.

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Presentation on theme: "Heart. Heart as a pump Two separate pumps –Right heart Blood to respiratory system –Left heart Blood to the peripheral organs."— Presentation transcript:

1 Heart

2 Heart as a pump Two separate pumps –Right heart Blood to respiratory system –Left heart Blood to the peripheral organs

3 Chambers –Atrium (Primer pump) –Ventricle Muscle composition –Atrial muscle –Ventricular muscle –Specialized muscles Excitatory Conductive

4 Atrial and ventricular muscles –Similar to skeletal muscles –Longer duration of contraction Excitatory and conductive fibers –Few contractile fibrils Contract freely –Automatic rhythmical electrical discharge –Conduction of action potential

5 Cardiac muscle –Striated –Arranged in a latticework Division Recombination Spreading –Myosin and actin filaments

6 Cardiac muscle –Syncytium Muscle cells connected to each other via intercalated discs Gap junctions (free diffusion of ions) –Action potential Many cells act as one large unit

7 Two different syncytium –Atrial syncytium –Ventricular syncytium Separation of atria from ventricle –Fibrous tissue surrounding atrioventricular (A- V) valvular openings Prevents atrial action potential from traveling to ventricle –Allows contraction of atria ahead of ventricles

8 Ventricular action potential –150 mV –Plateau (15 times longer contraction)

9 Cause of plateau and longer action potential –Fast Na channels –Slow Ca channels (Na-Ca channels) Longer flow of Na and Ca ions (prolonged deolarization) –Decreased K permeability after the onset of action potential Prevents flow of K out of the cells

10 Ventricular Muscle Action Potential Membrane Potential (mV) Seconds Fast Na + Channels Open Slow Ca ++ Channels Open phase K + Channels Open phase 0- Fast Na + channels open then slow Ca ++ channels phase 1- K + channels open phase 2- Ca ++ channels open more phase 3- K + channels open more phase 4- Resting membrane potential K + Channels Open More Ca ++ Channels Open More Copyright © 2006 by Elsevier, Inc.

11 Velocity of signal conduction –0.3 to 0.5 mSec Purkinje fibers Refractory period –Absolute refractory period 0.25 to 0.3 sec in ventricular muscle 0.15 sec in atrial muscle –Relative refractory period 0.05 sec Cause premature contraction

12 Excitation-contraction coupling Specific mechanism –Large influx of Ca from extracellular fluid via T-tubules (critical for generating stronger contraction) Poorly developed SR Larger T-tubules Mucopolysaccharides (negatively charged molecule) inside of the T-tubules –Ca ion storage

13 Cardiac cycle Between the beginning of one heartbeat to the beginning of next heartbeat –Initiated by spontaneous generation of action potential Sinus node –Action potential to atrium –Action potential to ventricles via A-V bundle Delayed by 0.1 sec

14 Diastole –period of relaxation –Blood fills the heart Systole –Contraction

15 Cardiac Cycle (cont’d) Figure 9-5; Guyton & Hall

16 Electrocardiogram and cardiac cycle –Five waves (P, Q, R, S, and T) Electrical voltages generated by the heart –P-wave Spread of depolarization through atria (contraction of atria) –Q, R, and S waves Depolarization of ventricle –T wave Repolarization of ventricle

17 Atria as primer pumps –80 % of blood flows directly through atria into the ventricle –20 % by contraction of atria Pressure changes in atria –a-wave (contraction) –c-wave (bulging of A-V valves due to ventricular contraction) –v-wave (filling of atria while A-V valve is closed)

18 Ventricles as pump Systole –Isovolumetric contraction Rapid rise in ventricular pressure A-V valve closure Contraction without emptying of ventricle –Ejection Opening of semilunar valve (aortic and plumonary) Rapid (first 1/3, 70% emptying) Slow (last 2/3, 30 % emptying)

19 Cardiac Cycle (cont’d) Figure 9-5; Guyton & Hall

20 Diastole –Dramatic fall of ventricular pressure after ejection Closure of semilunar valves –Isovolumic relaxation –Opening of A-V valves Rapid filling of ventricles (first 1/3 of diastole)

21 Cardiac Cycle (cont’d) Figure 9-5; Guyton & Hall

22 Stroke volume End-diastolic volume – ml Stroke volume/ejection fraction –70 ml End-systolic volume –40 to 50 ml Increased end-diastolic volume and decreased end-systolic volume –Greater stroke volume

23 Cardiac output –Stroke volume X # heartbeat (per minute)

24 Function of valves Tricuspid and mitral valves –Prevent backflow of blood from ventricle to atria –Open and close passively Changes in pressure –Chordae tendinea Connection between vanes of valve and papillary muscle Prevent valves from bulging too far during ventricular contraction

25 Aortic pressure curve Opening of aortic valves –Ventricular pressure –Stretching of aortic wall 120 mm Hg pressure –Continuous blood flow Closure of aortic valves –Decrease in aortic pressure –80 mm Hg pressure

26 Work output Two forms –Volume-pressure work (external work, major proportion) Moving blood from low pressure (vein) to high pressure (artery) –Kinetic energy of blood flow Acceleration of velocity to ejection speed through valves

27 Volume-pressure diagram Four stages associated with cardiac cycle –Period of filling End-systolic to end- diastolic volume –Isovolumetric contraction Valve closure –Ejection –Isovolumetric relaxation

28 Pre- and afterload Preload –Degree of muscle tension when contraction beigns –End-diastolic pressure Ventricle is filled –Abnormal Alteration in pressure of ventricular filling Left Ventricular Volume Left Ventricular Pressure A Increased preload

29 Afterload –Tension which the muscle exerts its contractile force –Corresponds to systolic pressure –Abnormal Arterial pressure (ventricle must contract against) Left Ventricular Volume Left Ventricular Pressure B Increased afterload

30 Regulation of heart pumping Intrinsic regulation –Changes in volume of blood flowing to the heart Autonomic nervous system

31 Intrinsic regulation Frank-Starling mechanism –Adaptation of the heart in response to increasing flow of blood from veins Venous return –Greater the stretch of heart muscle during filling, greater the force of contraction Greater the volume of blood being pumped –Stretching of right atrium

32 Ventricular function curves Stroke output curve –Relationship between atrial pressure and ventricular output

33 Ventricular function curves Ventricular volume output curve –Relationship between two ventricles Overall relationship –Filling of ventricle by increased atrial pressure Increased ventricular volume and strength of pressure


35 Role of autonomic nervous system Sympathetic nerves –Increases heart rate (70/min to /min) –Increases contraction force Increases amount of blood being pumped out Increases ejection pressure –Increase in maximum cardiac output by 2 to 3 X Addition to Frank-Starling mechanism –Decreases heart rate (30 %) if inhibited Sympathetic stimulation causes pumping to be maintained at 30 % above the level without stimulation

36 Parasympathetic nerves (Vagus nerves) –Innervates atrium –Strong stimulation can stop heartbeat for a few seconds –Heart “escapes” and beats 20-40/min as long as being stimulated –Decreases the strength of heart muscle contraction ( %) –Decreases ventricular pumping by 50 % or more

37 Effects on cardiac function curve –Right atrial pressure Controls cardiac output –Sympathetic stimulation Increased cardiac output –Parasympathetic stimulation Decreased cardiac output –Caused by: Changes in heart rate Changes in contractile strength of heart muscle

38 Role of ions Excess potassium (2 to 3 x above normal) –Dilation –Flaccid heart (soft/flabby) Decreased heart rate –Block conduction of cardiac impulses from atria to ventricle –Decreased resting membrane potential Calcium –Spastic contraction if excess –Flaccid when deficient

39 Rhythmic excitation of heart Components –Sinus node (sinoatrial/S-A) –Internodal pathway –Atrioventricular node (A-V node) –A-V Bundle –Bundle branches of Purkinje nerves

40 Rhythmic excitation of heart Special system –Generation of rhythmical electrical impulses Sinus node –Rapid conduction of impulses Internodal pathway A-V bundle Left and right bundle branches of Purkinje nerve –Spread impulse throughout the ventricle –Impulse delayed by A-V node

41 Sinus node Specialized cardiac muscle –Absent of contractile muscle filament –Smaller size (3 to 5  m) compared to surrounding atrial muscle (10-15  m) –Capable of self-excitation Controls the rate of beat –Entire heart Pacemaker Leaky membrane to Ca and Na ions –Cause of self-excitation

42 Higher resting membrane potential (-55 to - 60 mV) –Higher Na ion concentrations Generation of action potential –Slow Na channels –Rapid opening and closing of Na-Ca channels –Opening of K channel Hyperpolarization of membrane to bring membrane potential to -55 to -60 mV

43 Seconds Membrane Potential (mV) Threshold Sinus Nodal Fiber Na + Leak Slow Ca ++ Channels Open K + Channels Open more Ventricular Muscle fiber } “Resting Potential” Rhythmical Discharge of Sinus Nodal Fiber

44 Internodal pathways Action potential from S-A node –Spread throughout atrium and reach A-V node –Specialized fiber to increase speed of conduction (0.3 m/sec to 1 m/sec) –Three pathway Anterior Middle Posterior –Anterior interatrial band Transmit impulse from atria to the left atrium

45 A-V node Delayed conduction –Caused by reduced number of gap junction Greater resistance to conduction of ions –Emptying of atria before ventricular contraction

46 Internodal pathways –Initial conduction delay from S-A node to internodal pathway (0.03 sec) –About 0.1 sec (0.09 sec) delay from the time action potential arrives via internodal pathway –Another 0.04 sec delay in the penetration portion of A-V bundle –Total delay from S-A node to A-V bundle (0.16 sec)

47 Ventricular Purkinje system Purkinje fibers –A-V node through A-V bundle into the ventricle –Very large fiber Rapid conduction of action potential –Instantaneous transmission of action potential throughout the ventricle –High level of permeability by gap junction –Very few myofibrils

48 Action potential –One-way conduction Atria to ventricle Arrhythmia prevention –Prevention of re-entry Fibrous barrier between atria and ventricle –Insulator Left and right branches

49 Main Arrival Times S-A Node 0.00 sec A-V Node 0.03 sec A-V Bundle 0.12 sec Ventricular Septum 0.16 sec

50 Control of excitation Sinus node –Faster discharge rate compared to A-V node or Purkinje fibers Pacemaker Ectopic pacemaker (other parts of heart) –Shift from sinus node to A-V node or Purkinje fibers Excessive excitability Blockage of transmission –Delayed initiation of impulse (Stoke-Adams syndrome)

51 Control of rhythmicity Parasympathetic nerves (Vagus) –Release of acetylcholine when stimulated Increased permeability/leakage of K (hyperpolarization) –Decreased resting potential to -65 to -70 mV Decrease rate of rhythm by S-A node Decrease excitability of A-V junctional fibers

52 Sympathetic stimulation –Releases norepinephrine Increased Na and Ca permeability Increased resting membrane potential –Acceleration of self-excitation –Increased rate of sinus nodal discharge –Increased rate of conduction and level of excitability –Increased force of atrial and ventriclular contraction

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