Discuss how the Frank-Starling law of the heart helps to explain the influence of venous return on stroke volume.

Video transcript

Welcome back. Everyone. Here's our next problem. Identify the correct relation of Venus return with stroke volume, S V and cardiac output C O. According to the Frank Starling Law of the heart, a, an increase in Venus return has a negative effect on S V N C O B. An increase in Venus return has a positive effect on S V and C O C A decrease in Venus return has a negative effect on S V N C O or D A decrease in Venus return has a positive effect on S V N C O. So we know we are identifying this relation based on the Frank Starling law of the heart. So let's recall from our content video. What exactly that is? So I'll put F dash S law and in essence, in very plain words, this means that the heart pumps out any extra blood that gets delivered to it. What does this mean with regard to venous return stroke volume, cardiac output? And why? Well Venus return would be the amount of blood returned to the heart? So our Frank Sterling Law talks about any extra blood that gets delivered to the heart must be pumped out. So in the Franking law, we're talking about a case when Venus returned is increased. So a little up arrow there, this is because when you have more blood coming into the heart, the muscles of the heart particularly. So say, especially we're concerned with the left ventricle or L V are more stretched out. Now, imagine if you stretch out, for instance, a spring, the more you stretch out that spring, the greater the recoil will be when you let go. The same thing happens with these heart muscles, the more stretched out, they are by a greater volume of blood coming in, they will recoil when the muscles contract with greater force. So that means they're recoil is added to detraction force. And what happens when the left ventricle contracts, it ejects blood from the heart. So since that contraction will be extra strong, because you've got the contraction plus this extra recoil from the extra stretching, more blood will be ejected. So more blood ejected. And when we talk about blood being ejected, we are talking about stroke volume and cardiac output. Those both measure the amount of blood ejected in two different ways, stroke volume measures the amount of blood being ejected per contraction, cardiac output, the amount of blood ejected per minute. So the slightly different units, slightly different means of measuring, but both are measuring how much blood is ejected from the heart. So with all that in mind, we're talking about how is venous return, the amount of blood returned to the heart related to stroke volume and cardiac output, how much blood is getting pumped out? Well, we have that answer in our description of the Frank Sterling law, the heart pumps out any extra blood that gets delivered to it. So when Venus returned is up, is increased, the end result is more blood gets ejected. So with that in mind, let's look through our answer choices. We are talking about an increase in venous return. So we can eliminate choices C and D which are describing a situation where less blood gets returned to the heart. So an increase in Venus return and we know greater amount of blood coming in means greater amount of blood will be pumped out. So you'll see higher stroke volume and cardiac output, that measure of the amount of blood being injected. And that is choice B, an increase in Venus return has a positive effect on S V and C O will eliminate choice A since that says the increase in Venus return has a negative effect on S B N C O, meaning would decrease the amount of blood getting pumped out. So that's not correct. So again, the correct relation of Venus return with stroke volume and cardiac output. According to that Frank Starling law of the heart choice B, an increase in Venus return has a positive effect on S V and C O. See you in the next video.