PHIS 206 1st Edition Lecture 12 Outline of Last Lecture I Muscle Mechanics Skeletal Muscles II Smooth Muscles III Cardiac Muscles IV Atrial and Ventricular V Mechanism of Stimulation Cardiac Muscle VI Cardiac Cycle Outline of Current Lecture I How The Blood Works Mechanical II How The Blood Works Blood Flow III External Factors that Modify Cardiac Output IV Electrical Properties of the Heart V Conductive Fibers Current Lecture I How The Blood Works Mechanical Blood is a fluid Fluids always flow downhill high to low pressure Heart valves only 1 way valves Valves will open when pressure pushing in is greater than pressure pushing back From pulmonary it goes down Left Atrial and down Left Ventricular to systemic From systemic it goes down Right Atrial and down Right Ventricular to pulmonary Systole heart contracting Diastole heart relaxing soon will be 0 mmHg heart fills passively expands where heart is closed in membrane at the end heart begins to contract 1st atrial contracts o 70 of volume that enters ventricles before atrial contracts o Ventricular thicker stronger begins to contract exceeds atrial pressure so valve b w a v get pushed up Period of isometric contraction volume stays same only pressure is increased by ventricles As LV reaches 80 mmHg valve opens and blood flows from LV to aorta Period of ejection blood is being ejected from ventricles These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II III IV V from time of 80 mmHg to 120 mmHg heart begins to relax 0 mmHg and back to diastole o happens EVERY second End Systolic 50 mL End Diastolic 125 mL Stroke 75 mL Normal Cardiac Output 5 L minute 5 L in left will soon go to 5 L in right How The Blood Works Blood Flow Starling Law of Heart harder you heart ejects in stroke heart entering in diastole Summary cardiac output return Length Tension relationship gives heart the unique property of having input output External Factors that Modify Cardiac Output Parasympathetic decreases heart activity output Sympathetic increases heart activity output Sterling s Law is an INTERNAL factor Autoregulation if you exercise a muscle O2 increases arterials dilate smooth muscle relaxes when O2 increases o blood flows through o Venus return increases so heart pumps extra volume Electrical Properties of the Heart Since the stroke volume difference b w end systole and end diastole the heart gains efficiency if there is a time when every cell simultaneously relaxes or contracts Excitation every piece of heart muscle can spontaneously depolarize contract Fastest contraction S A Node S A Node depolarize with highest frequency spontaneously than any other heart cell Atrium have simultaneous relaxation contraction will stay that way until 1st cell that generated the action potential goes back to relaxation o cells are in the S A Node Conductive Fibers carry action potentials from atria to ventricles since they cannot directly transfer to each other What happens in atria occurs in ventricles but only timing is different
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