May 26, 2011

057 Pressure Reflexes and Mean Arterial Pressure

Here is an interesting concept about pressure reflexes that you might want to watch. It is related to the mean arterial pressure of a man. Learn more by watching another one of Leslie’s easy videos to help you understand these concepts easier.

Have fun!

Transcript of Today’s Episode

Hello and welcome to another episode of Interactive-Biology TV where we’re making Biology fun! My name is Leslie Samuel and in this episode, Episode 57, I’m going to talk about, ‘Pressure Reflexes and Mean Arterial Pressure.’ We’ve been talking about mean arterial pressure a lot, we’ve spoken about cardiac output and peripheral resistance. You can always revisit previous episodes to find out more about them.

Today, we are talking about pressure reflexes. We’ll look exactly at why we call it pressure reflexes. Here we have the heart (I feel like I keep saying that in very episode recently) and the heart, it pumps the blood throughout the body. We have the aorta.

One of the arteries that I have not been talking about would be the carotid artery. This is the common carotid. I’m just going to come here and draw a line here and say, that we’re dealing with carotid arteries. Of course, here, we are dealing with the aorta.

There is something very special that we have in these two arteries. In both the aortic and the carotid bodies, we have receptors that we call ‘baroreceptors.’ From the time you hear the prefix ‘baro-,’ you should know that it has something to do with pressure. For example, a barometer measures pressure and, here we have baroreceptors and these baroreceptors respond to changes in, you guessed it! Pressure. That is why they are called baroreceptors.

What’s going to happen is, if we have an increase in the mean arterial pressures, so we have a significant increase in mean arterial pressure, what that’s going to do, these baroreceptors are going to start firing. We’re going to have an increase in the firing of these baroreceptors. In other words, they’re going to be sending signals. Those signals are going to a region in the brain stem that we call the medulla. This is known as the “blood pressure regulating center.” Of course, it regulates other things but, it also regulates pressure.

That then, is going to cause a combination of two things. It’s going to cause an increase in parasympathetic activity and going to cause naturally a decrease in sympathetic activity. If you remember from one of the early episodes, sympathetic activity causes stuff like increase in heart rate, increase in blood pressure, and so on. Parasympathetic activity calms stuff down so, it reduces blood pressure, it reduces heart rate, breathing rate, and so on. So, we have an increase in mean arterial pressure, so an increase in blood pressure, the baroreceptors are going to respond by sending signals to the medulla. That’s going to cause an increase in parasympathetic activity, calming stuff down, and a decrease in sympathetic activity. Sympathetic activity would normally increase pressure, and speeds stuff up but, here we’re slowing that down. So, the net result of these two things is we’re going to get a reduction in cardiac output and also in peripheral resistance. Then, of course, that is going to cause a reduction in mean arterial pressure.

This is why we call it a reflex because we have an increase in mean arterial pressure, and that’s going to cause a number of things that’s going to eventually cause a reduction in mean arterial pressure. The relationships between these quantities here, we’ve looked at a number of times, and, just to revisit that:

M.A.P. =CP x PR,

Mean arterial pressure is equal to cardiac output times peripheral resistance. Since we’re decreasing both cardiac output and peripheral resistance, we are also going to decrease mean arterial pressure.

That’s pretty much it for this episode. Of course, you can always visit the website at for more Biology videos, more Biology resources, and more Biology fun. That’s it for now and I’ll see you in the next one.

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