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Physiology Lecture 10- Cardiac Cycle
And Cardiac Output Exam Study
Guide
phases of the cardiac output - Answer all events during a single heartbeat
phase 1: ventricular filling - Answer occurs during the mid to late diastole (ventricular relaxation); blood flows into the atria, through the AV valves, and into the ventricles. At this time, the semilunar valves are closed; toward the end of this phase, the atria contract to drive more blood into the ventricles
phase 2: isovolumetric contraction - Answer occurs at the beginning of systole. the pressure in the ventricle exceeds that in the atria and the AV valves close (generates first sound of the heartbeat); however the pressure is not great enough to open semilunar valves; thus, there is no blood flow into or out of the ventricle
phase 3: ventricular ejection - Answer ventricular pressure rises and blood is pushed through the semilunar valves. now, ventricular pressure drops and the semilunar valves shut (generates second sound of heartbeat); this ends systole
phase 4: isovolumetric relaxation - Answer as the ventricles enter the early stage of diastole, the pressure is still too high to allow AV valves to open, and too low to push semilunar valves open; thus, all valves are closed and no blood is moving through the ventricles as they relax
aortic (arterial) pressure - Answer pressure is measured in millimeters of mercury
diastolic pressure - Answer at the end of phase 2, the pressure in the aorta is at its minimum
systolic pressure - Answer during phase 3, as the ventricular pressure rises, the semilunar valve opens, the aortic pressure rises to a maximum
at the end of phase 3 - Answer as the ventricle pressure is dropping, the aortic pressure drops but remains higher and the difference causes the semilunar valve to close
mean arteriole pressure (MAP) - Answer the average arterial pressure based on the following equation
MAP - Answer (systolic pressure + 2 diastolic pressure) / 3
end-diastolic volume (EDV) - Answer during phase 1 (ventricular filling) - the ventricular volume is increasing and eventually reaches its maximum
end-systolic pressure (ESV) - Answer during phase 3 (ventricular systole) - the ventricular volume is decreasing and eventually reaches its minimum
stroke volume - Answer the amount of blood ejected form the ventricle during one heartbeat
SV - Answer EDV - ESV
average stroke volume - Answer 70 ml
ejection fraction (EF) - Answer stroke volume / end-diasolic volume ; average: 54% ; when the ventricle is completely relaxed, it holds 130ml, the SV on average is 70ml, so that means 60ml was not ejected
cardiac output (CO) - Answer the amount of blood pumped by the heart in one minute
cardiac output (CO) (ml/min) - Answer stroke volume (ml/beat) x heart rate (beats/min) ; average: 5.25 liters
neural control of heart rate - Answer controlled by two branches of our autonomic nervous system; sympathetic and parasympathetic
sympathetic ANS - Answer neurons release epinephrine and norepinephrine, which bind to adrenergic receptors on the SA (pacemaker) cells; as a result, funny channels and T-type calcium channels are opened and the frequency of action potential generation is increased
parasympathetic ANS - Answer neurons release acetylcholine, which binds to muscarinic cholinergic receptors on the SA (pacemaker) cells; as a result, T-type calcium channels and sodium channels close and potassium channels open; thus, the cell hyperpolarizes and action potentials decrease
epinephrine - Answer released from the adrenal gland in large amounts when we're under stress; increases heart rate; hormonal control of heart rate
ventricular contractility - Answer extrinsic (external) influence
sympathetic influence on stroke volume - Answer it not only causes an increase in heart rate but it also causes an increase in calcium activity such that the cell's contractile is maximized
epinephrine from adrenal gland (changes in stroke volume) - Answer causes increased heart rate, increase in calcium activity (cell's contraction is maximized)
thyroid hormone, glucagon, and insulin - Answer can increase force of contraction
influence of end-diastolic volume on stroke volume - Answer an intrinsic (internal) influence
starling's law - Answer when the rate at which blood flows into the heart changes, the heart automatically adjusts its output to match the inflow
if EDV increases - Answer force of ventricular contraction increases, SV increases, CO
