CH18 Cardiac Cycle

Exam 1 Review: Chapter 18: Cardiac Cycle

cardiac cycle - The complete sequence of events encompassing one complete contraction and relaxation of the atria and then the ventricles of the heart from the beginning of one heart beat to the beginning of the next; an electrical impulse (depolarization event) is conducted through the myocardium which constricts the atria which can be illustrated on an electrocardiogram.

systole - The period when either the ventricles or the atria are contracting; the rhythmic contraction of the heart, especially of the ventricles, by which blood is driven through the aorta and pulmonary trunk after each dilation or diastole during which the chambers are refilled; systole is also reflected in the systolic pulse pressure observed in the arterial tree.

extrasystole - A premature contraction of the heart, which is independent of the normal rhythm and arises in response to an impulse in some part of the heart other than the sinoatrial node, resulting in momentary cardiac arrhythmia. aka premature beat

PreVentricular Contractions (PVCs) - A premature contraction of the heart, when the ventricles fire early, before the atria; PVCs are among the less serious arrhythmias and usually do not need treatment; they are disconcerting, however, and they can happen in response to caffeine--coffee, tea, sodas and chocolate and some kinds of over-the-counter cough or cold medicines and alcohol.

diastole - The period of the cardiac cycle when either the ventricles or the atria are relaxing and fill with blood; diastole is also reflected in the diastolic pulse pressure observed in the arterial tree.

end-diastolic volume (EDV) - The typical volume of blood, approximately 120-130 mL, found in the ventricles after they are filled by atrial contraction during ventricular diastole (before the ventricles contract); the actual volume will depend on venous return of blood to the heart.

end-systolic volume (ESV) - The residual volume of blood, approximately 50-60 mL, found in the ventricles after systole (when the ventricles have contracted); the volume varies in response to activity levels and to disease states.

venous return - The amount of blood delivered to the atria by the veins of the pulmonary and systemic circulations; venous return is influenced by blood pressure, gravity, blood volume, activity levels and by disease states.

stroke volume (SV) - The amount of blood pumped out of a ventricle during one contraction; the difference between the ventricular end-diastolic volume (EDV) and the end-systolic volume (ESV); a typical stroke volume is approximately 70 mL; stroke volume is influenced by the contractility (inotropy) of the heart and by the preload (degree of venous return) and the afterload (the degree of arterial (pulmonary trunk or aorta) pressure).

quiescent phase (of cardiac cycle) - The period of relaxation, especially the time during which the valves to the heart chambers are closed and the myocardium is relaxing (see isovolumetric relaxation).

isovolumetric contraction - The period during the cardiac cycle in which the both the atrio-ventricular valves and the semi-lunar valves of the ventricles are closed and the myocardium is contracting; during this period the volume of blood in each ventricle does not change, but the tension on the myocardium and the blood pressure within the ventricles are increasing.

ventricular ejection - The period during the cardiac cycle in which the atrio-ventricular valves of the ventricles are closed but and the semi-lunar valves are open and the myocardium is contracting, moving blood into the pulmonary trunk and aorta; during this period the volume of blood in each ventricle, the tension on the myocardium and the blood pressure within the ventricles are decreasing; this period typically lasts 0.25 seconds.

isovolumetric relaxation - The period during the cardiac cycle in which the both the atrio-ventricular valves and the semi-lunar valves of the ventricles are closed and the myocardium is relaxing; during this period the volume of blood in each ventricle does not change, but the tension on the myocardium and the blood pressure within the ventricles are decreasing.

dicrotic notch - The portion of a graph of arterial blood pressure representing the sudden drop in pressure after systolic contraction caused by the flow back of blood in the arteries when the aortic semilunar valve is still in the process of closing and some blood is exiting the aorta into the coronary arteries.

List:

6. three fundamental physiological factors that affect stroke volume. Explain.

preload the degree of stretching of cardiac muscle cells before contraction which is determined primarily by the amount of venous return of blood to the atria and any circumstances that would alter venous return (the length-tension relationship)

contractility inotropic effects: the degree of contractile strength of the myocardium itself other than from the degree of stretch (the issue of optimal length of sarcomeres to initiate contraction); examples would be the influence of exercise or the lack thereof on cardiac muscle cells or the ability of epinephrine and norepinephrine and various therapeutic drugs to increase contraction by opening calcium channels or the impact of changing the concentrations of key ions such as calcium and potassium in the myocardium

afterload the pressure that must be overcome the the ventricles to eject blood from the heart; usually this is the arterial blood pressure which is influenced by blood volume and the various forces that influence resistance to flow

7. the phases and events of the cardiac cycle.

P wave atrial depolarization & contraction fills the ventricles cuspid valves open while valves of vena cava and pulmonary veins are closed

QRS complex atrial repolarization and relaxation & simultaneous ventricular depolarization and contraction empties the ventricles cuspid valves are closed while semilunar valves are open

T wave ventricular repolarization and relaxation heart relaxes cuspid and semilunar valves are closed

pause myocardium at rest atria fill after a pause of some length valves of vena cava and pulmonary veins open so atria can fill

preload	the degree of stretching of cardiac muscle cells before contraction which is determined primarily by the amount of venous return of blood to the atria and any circumstances that would alter venous return (the length-tension relationship)
contractility	inotropic effects: the degree of contractile strength of the myocardium itself other than from the degree of stretch (the issue of optimal length of sarcomeres to initiate contraction); examples would be the influence of exercise or the lack thereof on cardiac muscle cells or the ability of epinephrine and norepinephrine and various therapeutic drugs to increase contraction by opening calcium channels or the impact of changing the concentrations of key ions such as calcium and potassium in the myocardium
afterload	the pressure that must be overcome the the ventricles to eject blood from the heart; usually this is the arterial blood pressure which is influenced by blood volume and the various forces that influence resistance to flow

P wave	atrial depolarization & contraction	fills the ventricles	cuspid valves open while valves of vena cava and pulmonary veins are closed
QRS complex	atrial repolarization and relaxation & simultaneous ventricular depolarization and contraction	empties the ventricles	cuspid valves are closed while semilunar valves are open
T wave	ventricular repolarization and relaxation	heart relaxes	cuspid and semilunar valves are closed
pause	myocardium at rest	atria fill after a pause of some length	valves of vena cava and pulmonary veins open so atria can fill