Ch 13: Heart concepts:

SLOs Distinguish between pulmonary and systemic circuits. Trace a drop of blood through the heart and name all structures it passes by. Describe the cardiac cycle and explain how the pressure differences in the heart chambers account for blood flow through the heart Diagram EC coupling in cardiac muscle and compare it to EC coupling in skeletal muscle Distinguish between myocardial contractile cells and myocardial autorhythmic cells. Diagram the mechanisms by which APs are generated in each cell type Describe and trace the electrical conduction system. Describe the components of the ECG and their relationships to the cardiac cycle.

13.3 Structure of the Heart 2 circuits ... 4 chambers.... Fibrous skeleton Fig 13 -10

Pulmonary and Systemic Circulation 3 basic components: ? The heart is a dual pump!

One way flow in heart is ensured by ? AV = _______________________________ located between ..... Semilunar located between ..... Fig 13 -11

Heart Sounds (HS) lub....dub... 1st HS: during early, isovolumetric ventricular contraction (= ________________)  AV valves close 2nd HS: during early ventricular relaxation (= ________________)  semilunar valves close

Stethoscope Positions for Heart Sounds Heart Murmurs Clinical Application Abnormal, turbulent blood flow produces heart murmurs upon auscultation Stethoscope Positions for Heart Sounds Fig 13 -13

Many Causes for Heart Murmurs Defective heart valves: Stenosis, e.g.: Mitral stenosis  consequences? Incompetent valves  Insufficiencies, e.g.: Mitral valve prolapse  regurgitation (common)

Many Causes for Heart Murmurs cont. Septal defects: Holes in interventricular or interatrial septa Ductus arteriosus Normal Fig 13 -14 Various pathogenic

13.4 Cardiac Cycle

Mechanical Events of Cardiac Cycle Systole (time during which cardiac muscle contracts) atrial ventricular Diastole (time during which cardiac muscle relaxes) Fig 13 -17 Heart at rest: atrial & ventricular diastole Completion of ventricular filling: atrial systole Ejection: ventricular systole

Cardiac Muscle sSR smaller than in skeletal muscle, indicates ? Fig 12 -32 Heart muscle cells: 99% contractile 1% autorhythmic pacemaker cells sSR smaller than in skeletal muscle, indicates ? Abundant mitochondria

EC Coupling in Heart Muscle Voltage-gated Ca-channels are not directly connected to Ca-channels in SR Ca acts as 2nd messenger to open SR Ca-channels. Calcium-induced calcium release Fig 12-34

EC Coupling

13.5 Electrical Activity of the Heart and the Electrocardiogram Pacemaker or autorhythmic cells: Anatomically distinct from contractile cells Spontaneous AP generation  Do not need ___________ Unstable resting membrane potential = pacemaker potential

Pacemaker potential starts at -60mV, slowly drifts to threshold Fig 13.18 Heart Rate = Myogenic Skeletal Muscle contraction = ?

Modulation of Heart Rate by ANS ANS alters permeability of autorhythmic cells to different ions NE/E:  flow through If (HCN) and Ca2+ channels  Rate AND force contraction  Ach:  flow through K+ channels and  flow through Ca2+ channels  Heart rate 

Pacemaker sets HR SA node firing rates set HR Why? If SA node defective? ___________: 50 bpm ventricular cells: 35 bpm  Implant mechanical pacemaker!

APs in Contractile Myocardial Cells Similar to skeletal muscle Stable resting pot. ~ 85 - 90 mV Rapid depolarization due to voltage gated Na+ channels (Na+ movement?) Repolarization due to voltage gated K+ channels (K+ movement?) What is different?

Compare to Fig 13-19

Refractory Period and Summation of Skeletal Muscle

Refractory Period and Summation of Cardiac Muscle Fig 13.21

Electrocardiogram ECG (EKG) Reflects electrical activity of whole heart not of single cell! Surface electrodes record electrical activity deep within body - How possible?

Signal very weak by time it gets to skin EC fluid = “salt solution” (NaCl)  good conductor of electricity to skin surface Signal very weak by time it gets to skin ventricular AP = ? mV ECG signal amplitude = 1mV EKG tracing =  of all electrical potentials generated by all cells of heart at any given moment (e)

Depolarization = signal for contraction Since: Depolarization = signal for contraction Segments of EKG reflect mechanical heart events Mechanical events lag slightly behind electrical events. Fig. 13-22

Components of EKG Waves: P, QRS, T Segments: PR, ST Intervals = wave-segment combos: PR, QT

Net electrical current in Why neg. tracing for depolarization ?? Net electrical current in heart moves towards + electrode EKG tracing goes up from baseline Net electrical current in heart moves towards - electrode EKG tracing goes Down from baseline

Einthoven’s Triangle and the 3 Limb Leads: RA LA LL I II III – + Fig 13.24

Relationships of EKG components Info provided by EKG: HR Rhythm Relationships of EKG components each P wave followed by QRS complex? PR segment constant in length? etc.

For the Expert: Find subtle changes in shape or duration of various waves or segments. Indicates for example: Change in conduction velocity Enlargement of heart Tissue damage due to ischemia (infarct!)

Normal and Abnormal EKGs In depth study in lab Analyze this abnormal ECG:

ECG, Pressures and Heart Sounds The end