Hi, everyone. In this video, we're going to begin our introduction to tissues and histology. And so we already know that the human body is amazingly complex. I mean, just look at us. We've got trillions of cells and hundreds of different cell types.
However, despite all of this amazing complexity, the human body is only built from just 4 primary types of tissue or 4 main types of tissue. And so 4 is a pretty manageable number, not too bad. And so in this video, we're only going to briefly introduce these 4 primary types of tissues in this illustration down below. But as we move forward in our course, we'll talk about each of these 4 primary types of tissues in a lot more detail, covering their characteristics, including their structures and their functions. And so before we actually introduce these 4 primary types of tissues, let's first recall from some of our previous lesson videos what the term tissues even means.
And so recall from those previous lesson videos that the term tissues can be defined as groups of similar cells that are working together to perform related functions. And so it's important to note that the cells within a particular tissue are going to be similar in nature but not necessarily identical. And it's also important to note that the term tissues itself, in addition to referring to the groups of cells, can also include the extracellular matrix or the ECM for short, which can be briefly defined as the surrounding material immediately outside of the cells. And so moving forward in our course, we're going to talk more details about the composition of the extracellular matrix. But for now, in this video, the bigger takeaway that I'd like you to walk away with is that the term tissues can be defined as not just the groups of similar cells but also their extracellular matrix.
Now, it's also important to note that all 4 of the primary types of tissues have an extracellular matrix. Although the extracellular matrix can be more prominent in some types of tissues versus other types. But those are some details that we'll get to talk more about as we move forward in our course. But for now, let's take a look at our illustration down below where we can finally introduce the 4 primary types of tissue. And so the first primary type of tissue that we're going to cover is epithelial tissue.
An epithelial tissue is going to be important for covering surfaces, lining cavities, and forming glands. And so over here, we have a micrograph of some epithelial tissue. Now the next type of tissue is going to be connective tissue. And connective tissue is actually the most abundant tissue throughout the human body and it's the most diverse tissue in terms of its structure and its function. And connective tissue is also going to have the most prominent extracellular matrix.
And so here we have a micrograph of some connective tissue. Now, the third type of tissue is going to be muscle tissue. And so as you probably already know, muscle tissue is going to be important for contracting in order to allow for body movements. And then last but not least, our 4th type of primary tissue is going to be nervous tissue. And nervous tissue is going to be important for detecting stimuli in our environment and transmitting electrical signals.
And so once again, this is just a brief introduction to these 4 primary types of tissues. And as we move forward in our course, we'll get to talk a lot more details about them. And so we'll also get to define what the term histology means in one of our next videos. And so this concludes this video, and I'll see you all in our next video to get some practice.