Influence on Pacemaker Activity – Heart Rate and Electricity

by Thad Wilson, PhD

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    Now, we have pacemaker activity. We talked about the most important things. That was how the nerves control the heart rate. Let's talk about a couple other things that control heart rate because it's not only about the nerves, although it’s mainly about the nerves. It’s not only about the nerves. There are a few hormones that can affect heart rate, such as you have a high amount of thyroid hormone. So, that's T3, T4 in a hyperthyroid condition. You have an increase in heart rate. If you have low thyroid hormones, T3 and T4, you have a low heart rate. Catecholamines can increase heart rate. Now, what do we mean by catecholamines. Catecholamines is a broad term that we use for epinephrine and norepinephrine. Now, these are ones that are circulating around in the body, not necessarily what is released by the nerves that will bind directly to the SA node. So, these are circulating hormones traveling around in the blood, traveling around in the blood. We are mainly talking about epinephrine, norepinephrine or adrenaline and noradrenaline. Those increase heart rate. We have a few ions that also can change heart rate. Potassium is probably our biggest one we want to think about. If potassium levels are high, heart rates are a little bit lower. If potassium levels are lower, heart rate is higher. So, they kind of work in an inverse relationship between potassium and heart rate. Why this might occur? Think of how that potassium changes resting membrane potential. So, if you have a lower resting membrane potential versus a higher resting membrane potential, that's going to affect the speed at which or the distance that phase 4 will reach threshold. A couple other things that affect heart rate. Ischemia is a big one. So, what is...

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    The lecture Influence on Pacemaker Activity – Heart Rate and Electricity by Thad Wilson, PhD is from the course Cardiac Physiology.

    Author of lecture Influence on Pacemaker Activity – Heart Rate and Electricity

     Thad Wilson, PhD

    Thad Wilson, PhD

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