Alright. So we're going to get started on that myogenic mechanism. This is an internal regulation technique. It involves the kidneys engaging in autoregulation and maintaining the glomerular filtration rate all on their own. The myogenic mechanism adjusts the afferent arteriole in response to normal minor daily changes in blood pressure. If you recall from a few chapters back, to help us maintain homeostasis, vascular smooth muscle responds to changes in blood pressure; it contracts when it's stretched and relaxes when it's not stretched. And that is actually where the name of this mechanism comes from. Remember that 'myo' means muscle, and so the myogenic mechanism reflects a property of vascular smooth muscle in our body. Our main stimulus here is going to be stretching or a decrease or absence of stretch within our afferent arteriole. This is going to signal to the kidneys whether blood pressure has increased or decreased. I'm going to walk you through exactly what would happen if there was an increase or decrease in blood pressure.
First, we're going to imagine that we have an increase in systemic blood pressure. This increase in blood pressure would lead to an increased stretch in the smooth muscle of the afferent arteriole. Because more blood is coming in faster, it's going to stretch that vascular smooth muscle. This would trigger a reflex, and the arteriole would contract. The contraction of the afferent arteriole restricts blood flow into the glomerulus. By doing that, our glomerular filtration rate will be maintained at a normal range. Now, if we go down to our little image here, again, just picture we are constricting that afferent arteriole, which is the equivalent of turning down the sink, and now less blood can get into the glomerulus. So, even though blood pressure in the whole body has increased, the glomerulus is receiving the correct amount of blood to maintain a glomerular filtration rate.
If we were to have a decrease in systemic blood pressure, we would have decreased stretch in the smooth muscle of the afferent arteriole. And so, our arteriole would relax. This relaxation or dilation would increase blood flow into the glomerulus, and our GFR would be maintained at a normal range. So, once again, imagine we are dilating that afferent arteriole, like turning up the faucet basically. Even though systemic blood pressure has decreased, the kidneys are receiving the correct amount of blood to maintain the glomerular filtration rate.
Alright. That is our myogenic mechanism, and I'll see you guys in the next one. Bye-bye.