Fill in the blanks: An increase in preload causes a/an_____ in stroke volume in accordance with the_____ law. An increase in afterload causes a/an ______in stroke volume. An increase in contractility causes a/an______in stroke volume.

Video transcript

Hi everyone. Let's take a look at this practice problem together. The following can increase the cardiac output except the answer options are a increased heart rate. B, increased contraction of trabecula carn C increase in preload and d enhanced contractility in the ventricles. So what is cardiac output? Recall, what the equation is to calculate cardiac output. Cardiac output equals the heart rate multiplied by stroke volume. And cardiac output is defined as the amount of blood pumped by the heart in one minute stroke volume is defined as the amount of blood pumped by the left ventricle with each contraction. So factors that will increase the cardiac output will be things that increase the heart rate or increase the stroke volume. Option, a increased heart rate. This will lead to increased cardiac output. So we can eliminate option a option C increase in preload. Recall that preload is the amount of stretch cardiac muscle cells have at the end of ventricular feeling. So if there is increase in preload, there is more stretch in those muscle cells and that will lead to a larger contraction and this larger contraction can lead to increased stroke volume. So option C is not the exception and is not the correct answer. Option D enhanced contractility in the ventricles. Again, enhanced contractility will produce a stronger contraction and a stronger contraction will lead to increased stroke volume. So we can eliminate option D. The correct answer is the increased contraction of trabecula Carney recall that Trabecula carna are muscular ridges on the inner surface of the ventricles. Their contraction plays a role in the heart valve functioning but it does not affect heart rate or volume and therefore cannot increase cardiac output. So the correct answer is option B, increase contraction of trabecular carnea. All right, everyone. I hope you found this helpful and I'll see you soon for the next practice problem.