In this video, we're going to talk about the 3rd type of muscle tissue in our lesson which is smooth muscle tissue. And so, smooth muscle tissue is actually named for its smooth appearance under the microscope. And so, the smooth muscle tissue gets its smooth appearance due to the lack of striations in smooth muscle tissue. And so, it turns out that the lack of striations is a feature that is unique to smooth muscle tissue. And so recall from our previous lesson videos that the other two types of muscle tissue, skeletal muscle tissue and cardiac muscle tissue, are both striated, meaning that they have a banded appearance.

And again, smooth muscle tissue is going to be unique in that it lacks those striations and that is what gives it the smooth appearance under the microscope. Now, in terms of the location of where smooth muscle tissue can be found within the body, we can pretty much say that any involuntary muscle tissue that's not part of the heart is going to be smooth muscle tissue. But more specifically here, we can see that smooth muscle tissue can be located in the walls of several hollow internal structures within the body. For example, smooth muscle tissue is found in the walls of blood vessels, they're also found in the walls of intestines that make up part of the digestive system, and they're found in the walls around the bladder. And so, in terms of the function of smooth muscle tissue, we can say that it's going to control the diameter of these hollow internal structures, and it can help propel the material through the organs.

For example, we know that the smooth muscle tissue that is found in the intestines of the digestive system are going to contract in order to decrease the diameter of the intestines and to propel food through the digestive system in a specific direction. Also, blood vessels, the smooth muscle tissue that is, in the walls of the blood vessels can contract to decrease the diameter of the blood vessels to increase the blood pressure in those blood vessels. And also, the smooth muscle tissue that surrounds the bladder can contract in order to help to release the urine from the bladder. Now, it is worthy of noting that the bladder does actually have some skeletal muscle tissue that is voluntary that allows us to control when we release the urine from the bladder. Now, smooth muscle tissue, as we already know, is going to be involuntary in its nature, just like cardiac muscle tissue.

And so, this means that its contractions are not going to be consciously controlled. And so, we can't really think about the smooth muscle tissue in our intestines and consciously control their contractions. And so this is what makes it involuntary. And again, skeletal muscle tissue is unique in its voluntary nature. Now, in terms of the shape of the smooth muscle tissue cells, it's notable that they are going to consist of short and spindle shaped cells.

And so, the short and spindle shaped cells are going to be thin on the ends and thick in the middle just like a spindle. And so notice over here on the far right we're actually showing you an image of a spindle and thread in case you needed a better visualization of what this spindle shape looks like. And so we're focusing in on this green part here and that is the spindle shape. And again, you can notice that on the edges it's going to be thinner, but then in the middle it's going to be thicker and that's exactly what we're describing right here. Now, because these smooth muscle tissue cells are relatively short, then one single nucleus per cell is usually sufficient.

And that means that these cells are going to be uninucleate in nature. Which again means that the smooth muscle cells are each going to have just one nucleus. And so, let's take a look at our image down below where we can start to piece things together here. And so again, when it comes to smooth muscle tissue, it's going to have a smooth appearance under the microscope due to the lack of striation, a unique feature of smooth muscle tissue. And again, in terms of the locations, smooth muscle tissue is pretty much involuntary muscle tissue that is not found in the heart.

And so, it can be found in many different locations, but we know, once again from our lesson up above, that they're found in the walls of several hollow internal structures, including the walls of the intestines of the digestive system. And so notice in our image down below we're focusing in on the digestive system and the walls of the intestines. And so notice we're showing you a micrograph here of smooth muscle tissue and notice that it does have a pretty smooth appearance. We don't really see these striations like what we saw in the skeletal muscle tissue and cardiac muscle tissue. So, there is a lack of striations giving it a smooth appearance.

Also, notice that these cells are spindle shaped cells. And so notice that here, we are actually highlighting the shape of one of these smooth muscle tissue cells so that you can see that it is indeed spindle shaped. And also, notice that these cells are going to be relatively short, and so that means that they are going to be uninucleate, with just one single nucleus and that is usually sufficient for these smooth muscle tissue cells. And so the nuclei are these darkened circles that you see here and, each of these darkened circles would represent 1 muscle tissue cell, smooth muscle tissue cell. And so this here concludes our brief lesson on smooth muscle tissue, and we'll be able to get some practice applying these concepts as we move forward.

So I'll see you all in our next video.