1 Topics to be addressed: Blood Anatomy of Blood Vessels Anatomy of the Heart The Conduction System The Cardiac Cycle Cardiodynamics Blood Flow and its Regulation Adaptation and Disorders of the Cardiovascular System Overview of the Cardiovascular System

2 Pumping Blood: a mechanical event initiated by electrical events Purkinje fibers distribute the stimulus to the contractile cells, which make up most of the ventricle wall Normally, the SA node generates an action potential, and passes the signal down the conductive system The Cardiac Cycle and the ECG

3 Small size Single, central nucleus Branching interconnections between cells Intercalated discs Characteristics of Cardiac Muscle Cells

4 Structure of Cardiac Muscle Cells: Intercalated Discs

5 Structure of Cardiac Muscle Cells Intercalated discs contain two types of cell-cell junctions: Desmosomes physically tie cells together Gap Junctions connect cytoplasm allow ion flow directly from one cell into another “electrical coupling”

6 The Action Potential of a single contractile cardiac muscle cell **The resting membrane potential of contractile cells is stable (unlike that of the conductive cells like those of the SA node) Net gain of + charge Net loss of + charge

7 The Role of Calcium Ions in Cardiac Contractions Cardiac muscle tissue is very sensitive to extracellular Ca 2+ concentrations Calcium channel blockers are a group of powerful medications for heart patients Contraction of a cardiac muscle cell is produced by an increase in calcium ion concentration around myofibrils From Silverthorn Human Physiology, 4 th ed., Pearson/Benjamin Cummings 2007 Actin-Myosin crossbridges form

8 Comparison of the action potential and resulting contraction between skeletal and cardiac muscle In skeletal muscle, the action potential was brief relative to the contraction. A second action potential soon after the first increased cytoplasmic calcium levels and increased the contraction

9 Comparison of the action potential and resulting contraction between skeletal and cardiac muscle In cardiac muscle, the action potential lasts longer than the contraction. One contraction is over before another can begin, preventing summation of contraction and tetany. This ensures time for the heart to fill between contractions. The Absolute Refractory Period is very long: cardiac muscle cells cannot be stimulated again until this period is over

10 Monitoring Heart Activity: the ECG The Electrocardiogram (ECG or EKG) is a recording of electrical events in the heart, representing ALL the action potentials from ALL the cardiac cells – conducting and contractile

11 Features of an ECG P wave: Atria depolarize QRS complex: Ventricles depolarize T wave: Ventricles repolarize

12 Common Clinical ECG Measures P–R interval Time from start of atrial depolarization to start of QRS complex Q–T interval Time from ventricular depolarization to ventricular repolarization

13 Abnormal ECG Recordings Normal P waves absent SA node nonfunctional Slower heart rate now driven by AV node P waves not always followed by QRS wave A form of “heart block” Problem within conduction system between SA node and rest of system Chaotic deflections “Ventricular fibrillation” Bad. Very bad.

14 Defibrillators shock the heart back into a normal rhythm Portable AEDs (automated external defibrillators) are now common

15 The Cardiac Cycle One cycle = from the start of one heart beat to the start of the next heartbeat Two Phases: Systole (contraction) Diastole (relaxation) Begins with initiation of action potential at SA node Produces action potentials in cardiac muscle cells (contractile cardiac cells) of Atria Both Atria begin contracting = Atrial Systole Signal is transmitted through conducting system (conducting cardiac cells of AV node, Bundle branches, Purkinje fibers) Both Ventricles contract, apex to base, pushing out blood = Ventricular Systole atria begin relaxing = Atrial Diastole Ventricles relax, heart refills = Ventricular Diastole

16 The Cardiac Cycle The period between the start of one heartbeat and the beginning of the next What makes blood move? 1.A pressure gradient Blood moves from area of high pressure to area of low pressure 2.Open valve

17 Steps in the Cardiac Cycle Initiated by pacemaker potential at SA node

18 Steps in the Cardiac Cycle Ventricles are contracting and exerting pressure, but valves are closed so blood is unable to move out “Isovolumetric contraction” phase

19 Steps in The Cardiac Cycle Pressure generated by ventricle wall finally great enough to exceed trunk pressure; semilunar valves are pushed open “Ejection” phase

20 Steps in The Cardiac Cycle Ventricle wall begins relaxation, with pressure falling below trunk pressure. Back flow of blood from trunk toward ventricle closes semilunar valve and ends ejection phase

21 Steps in The Cardiac Cycle Ventricle wall relaxed, with pressure falling below that in atria; AV valves open as blood moves from atria to ventricles “Filling” stage

22 The Cardiac Cycle Looking at only the electrical events and resulting contractile events

23 The Cardiac Cycle Plotting pressures generated by atrial and ventricular contraction

Comparison of Right and Left Heart Pressures 24

25 The Cardiac Cycle Changes in blood volume are driven by changes in pressure and state of the valves

26 Heart sounds normally heard during the Cardiac Cycle “Lub” = S 1 Produced by turbulence as AV valves close and blood pushes against them “Dub” = S 2 Produced by turbulence as semilunar valves close and blood pushes against them Heart Murmur : Abnormal sounds produced by regurgitation through faulty valves or by damaged valve flaps

27 The Cardiac Cycle

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