Physio Exam 3 Questions With Accurate Answers

Physio Exam 3 Questions With Accurate Answers. Describe the Frank-Starling law of the heart - answerThe Frank-Starling law of the heart states that the stroke volume is directly proportional to the preload; an increase in EDV results in an increase in Stroke volume. The EDV is the amount of blood in the ventricles directly before the ventricles begin to contract so it can be referred to as the preload. Stroke volume is also directly proportional to the contractility of the heart in that when the ventricles contract with more force, they pump more blood and thus increase the stroke volume. What would happen to the pump rate of the heart if the stroke volume is increased? - answerIn order to maintain the cardiac output, the pump rate would decrease Describe how the heart alters stroke volume - answerit alters contractility or the preload Describe the intrinsic factors that control stroke volume - answerThe stroke volume is regulated by three variables: 1. EDV (volume of blood in the ventricles at the end of diastole) 2. Total Peripheral Resistance (the frictional resistance/impedance of blood flow in the arteries) 3. Contractility (the strength of ventricular contractions) Venous return to the heart will directly affect the afterload or the preload? - answerVenous return to the heart will directly affect the preload Increased heart contractility will result in? - answerIncreased end systolic volume How does the heart provide for an increase in stroke volume? - answerIncrease contractility ESV is equal to? - answerESV = EDV - SV Which of the following could cause an increase in peripheral resistance in blood vessels? - Vasodilation - Atherosclerosis - decrease in flow rate - decrease in stroke volume - answerAtherosclerosis will cause an increase in peripheral resistance in blood vessels What is the type of resistance increased in Aortic Valve Stenosis? - answerIn Aortic Valve Stenosis, there will be an increase in left-ventricular afterload What effect does compensation (regardless of type) have on heart rate? Explain. - answerCompensation increases heart rate but the increase does not go up to the "normal" heart rate. When there is a greater afterload (due to the narrowing of systemic blood vessels), the heart compensates by increasing contractility and preload (EDV). The myocardium of the left ventricle thickens to increase contractility. This hypertrophy limits the increase in preload because the increased stiffness of the myocardium prevents normal filling. To maintain the same cardiac output through compensation, heart rate increases. What effect does increasing preload have on cardiac output? Explain - answerIncreasing preload increases cardiac output. According to the Frank-Starling law, an increase in blood filling the ventricles leads to more myocardium stretching. This results to stronger contractions and increased stroke volume. The increase in stroke volume means an increase in cardiac output. What effect does aortic stenosis have on cardiac output? Explain. - answerAortic stenosis is the narrowing of the aortic semilunar valve. It decreases cardiac output, which means less blood is ejected per beat (and per minute). This is due to the increase in total peripheral resistance and increase in afterload. Give an example of one way to naturally increase preload - answerincreasing the pulmonary vein radius (increase blood flow from the lungs to the heart), led to an increase in preload. Preload can be naturally increased through sympathetic stimulation (i.e., increased skeletal muscle contraction through exercise) that increases venous return to the heart and thus, increased ventricular filling (EDV) What effect does increasing contractility have on cardiac output and pressure? Explain - answerIncreasing cardiac contractility increases the stroke volume, and consequently, would increase the cardiac output. When cardiac output is increased, the blood pressure would also be increased if total peripheral resistance remained the same. Give examples of factors that can naturally increase contractility. Give examples of factors that can naturally decrease contractility. - answerFactors that can naturally increase contractility: positive ionotropic factors that can increase sympathetic stimulation (i.e., exercise). Factors that can naturally decrease contractility: negative ionotropic factors that can stimulate the parasympathetic nervous system (i.e., relaxation and meditation). What effect does decreasing afterload have on cardiac output? Explain. - answerAfterload is the amount of pressure that the heart has to work against to pump/eject blood out of the ventricles. Decreasing afterload would lead to an increase in cardiac output. Decreasing the resistance or pressure that the left ventricle has to overcome, results in an increase in the stroke volume, and thus an increase in cardiac output. How does our body naturally decrease afterload? - answerOur body naturally decreases afterload by vasodilating blood vessels. This leads to a decrease in resistance (and thus, decrease in afterload). Why are extrasystoles not observed during the contraction phase? - answerExtrasystoles are not observed during the contraction phase, due to the longer refractory period of the cardiac action potential. Sequential action potentials cannot induce another cardiac contraction during the refractory period. Why is it important that summation not occur in heart muscle? - answerSummation is not possible because relaxation must be complete before the next contraction. This is due to the long absolute refractory period. If summation occurred in heart muscle leading to tetany, this could result in muscle fatigue. In this case, the heart would not be able to pump blood and cardiac output would be severely reduced. Why do you think the heart has a compensatory pause after extrasystoles? - answerThe compensatory pause after extrasystoles allows the cardiac muscle time to recover. What effect does stimulating the vagus nerve have on heart rate? From which subdivision of the autonomic nervous system (ANS) does the vagus nerve carry motor fibers? - answerStimulation of the vagus nerve decreases heart rate through the opening of potassium channels in the pacemaker cells. The vagus nerve supplies motor parasympathetic fibers to all organs (except the adrenal glands) from the neck down. Research has shown that in the absence of any neural or hormonal influences, resting heart rate is 100 bpm. However, average heart rate is 70 bpm. Explain this difference. - answerThe natural periodicity of the pacemaker cells in the heart is around 100 bpm. However, under normal physiological conditions, there is a tonic parasympathetic stimulation of the vagus nerve to the heart, which decreases the heart rate to its normal rate of 70 bpm What was the effect of temperature on heart rate? Why? - answerIncreasing temperature increases h