Lecture 11.2 Heart Physiology

Conduction System of the Heart Intrinsic/Nodal System: spontaneous, independent of nervous system Causes heart muscle depolarize from atria to ventricles. Sinoatrial (SA) Node - starts each heartbeat, “pacemaker” Arterioventricular (AV) Node AV bundles, bundle branches, Purkinje fibers

Electrocardiography Electrocardiogram (ECG) measures electrical current through the heart. Typical ECG wave = 1 heartbeat P wave - depolarization of atria before they contract QRS complex - depolarization of ventricles T wave - repolarization of ventricles

Electrocardiography

The Cardiac Cycle Cardiac Cycle - one complete heartbeat Atria contract simultaneously As atria relax, ventricles contract

The Cardiac Cycle Systole = contraction Diastole = relaxation We concentrate primarily on ventricular systole and diastole.

Heart Sounds - The “Lub Dup” “Lub” - closing of AV valves (beginning of systole) “Dup” - closing of semilunar valves (end of systole) LubLubDupDup

Cardiac Output Cardiac Output (CO): amount of blood pumped out by each ventricle each minute Stroke volume (SV): amount of blood pumped out by a ventricle with each heartbeat Heart Rate: Number of times the heart beats per minute. CO = SV x HR

Regulation of Heart Rate If stroke volume declines, HR must increase. Blood loss, weakened heart HR affected by ANS Sympathetic speeds up HR Parasympathetic slows down HR

Arterial Pulse Arteries expand and recoil with each heartbeat. Pulse: Pressure wave that travels through arteries Pulse can be felt in superficial arteries Average ~ 70 bpm at rest

Blood Pressure Blood pumped out through arteries is under pressure. Highest in arteries near heart Flows from high pressure -> low pressure on its way back to the heart. High BP: High blood volume, plaques, vasoconstriction (cold, nicotine…), sympathetic NS

Measuring Blood Pressure Heart alternately contracts and relaxes. Systolic Pressure: pressure in arteries when ventricles contract Diastolic Pressure: pressure in arteries when ventricles relax. Written as systolic/diastolic (ex: 120/80)