Conduction cells Autorhythmic, pacemaker

2 Types Cardiac Muscle Cells: Contractile cells

Seen in histology

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Activity of Autorhythmic Cells

Found in SA & AV nodes

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Conduction System of Heart Autorhythmic

(self excitable)

SA node Pacemaker

potential

AV node

AV bundle of His Divides into

bundle branches & purkinje fibers

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Impulse Conduction In Heart

SA node Atria AV node Bundle of His Bundle branches & Purkinje fibers Ventricles

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Action Potential in a Ventricular

Contractile fiber

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Physiology of Muscle Contraction Depolarization triggers contraction Plateau maintains contraction Repolarization triggers relaxation

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Electrocardiogram - ECG or EKG

P wave

PQ interval

QRS complex

T wave

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Cardiac Cycle All events associated with one heartbeat Systole & diastole of atria & ventricles

In each cycle, atria & ventricles alternately contract & relax

Forces blood from higher pressure to lower pressure During relaxation period, both atria & ventricles

are relaxed The faster the heart beats, the shorter the

relaxation period Systole & diastole lengths shorten slightly

Phases of the Cardiac Cycle

Linking ECG to AP & Contraction Action

Potentials in Atrial & Ventricular Contractile Cells

ECG Readings

Systole & Diastole in Heart Chambers

Heart Valve Openings& Closings 48

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Arrhythmia

Categories:

Supraventricular or atrial

Ventricular

Bradycardia

Tachycardia

Fibrillation

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Ventricular Pressures

BP in aorta is ~120mm Hg BP in pulmonary trunk is ~30mm Hg

Differences in ventricle wall thickness allows heart to push same amount of blood w/ more force from L ventricle Volume blood ejected from each

ventricle is ~70ml = stroke volume

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Cardiac Output Amount of blood pushed into aorta or pulmonary

trunk by ventricle CO = SV (stroke vol) x HR (heart rate)

Example: 70ml stroke volume & 75 beat/min

- CO = 70mL/beat X 75 beat/min = 5250 mL/min (5.25 L/min)

Cardiac reserve = difference between max CO & CO at rest average is ~4-5 resting volume while athlete is 7-8 resting volume heart disease may decrease the reserve

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Clinical Application: Congestive Heart Failure

Loss of pumping efficiency

Causes of CHF CAD, HTN, MI, valve disorders,

congenital defects

Left side heart failure Blood remains in ventricle Pulmonary edema

Right side failure Peripheral edema

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Regulation of Heart Rate & Contractility:Autonomic (nervous) control Cardiovascular center input from:

Cortex, limbic system, hypothalamus Proprioceptors Chemoreceptors Baroreceptors (pressure receptors)

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Regulation of Heart Rate & Contractility:Autonomic (nervous) control

Output: to heart (balancing act) Sympathetic impulses Parasympathetic impulses

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Regulation of Heart Rate & Contractility:Autonomic (nervous) control

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Variables That Influence Stroke Volume

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Chemical Regulation of Heart Rate

Hormones Epi & norepi

(from adrenal medulla)

Thyroid HM Cations

Relative [ ] K+, Ca+2 & Na+ = significant effect on cardiac fxn Other Factors:

Age Gender Physical fitness Body temp

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Disorders: Homeostatic Imbalances

Risk factors in heart disease: High blood cholesterol level HTN Cigarette smoking Obesity & lack of regular exercise Other factors include:

DM Genetic predisposition Male gender High blood levels of fibrinogen Left ventricular hypertrophy

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Plasma Lipids & Heart Disease

High blood cholesterol promotes growth of fatty

plaques lipids transported as

lipoproteins- HDL - LDL- VLDL

2 sources of cholesterol in body foods & from liver

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Exercise & the Heart

Benefits of aerobic exercise:

increased CO

increased HDL & decreased

triglycerides

improved lung fxn

decreased BP

weight control