After learning about plant tissues, let us take a look at the various types of animal tissues in details. In case of animals, where the body is expected to perform uncountable functions simultaneously, it is obvious that the number of tissues will also be innumerable, right? So how do we study all these? Well, we don't need to worry!
For simplicity, We would prefer dividing all the animal tissues into four major categories depending upon their functions. Firstly, we have the one for protection, then another for connection, followed by movement and locomotion, and lastly for transmission of signals for quick and efficient work. Based on this, we get the four major types of tissues as epithelial, connective, muscular and nervous.
So in this video, Let's begin with the first type that is the epithelial tissue. As the name says, epi is above, thus epithelial tissue is the one which lies above the entire body forming a protective covering. Along with covering the body, it also forms a barrier between the various organs separating them.
Now the structure of the epithelial tissue is quite evident from its function. Yes, since it has to perform a protective layer it cannot afford to have spaces between the cells. Hence, we find the epithelial tissue to have tightly packed cells forming continuous sheets.
The tissues lack intercellular spaces and has extremely small amount of cementing material. So every single substance that passes in or out of the cells needs to cross the epithelial layer at least once. Accordingly, the permeability of cells will differ in various epithelia depending upon the exchange of materials. Now when we talk about all the epithelial cells in general, we need to first understand a common characteristic between them.
May it be any different type of epithelia, all of them will always have the cells resting on a thin fibrous supportive membrane-like structure. This is called the basement membrane. The basement membrane, apart from supporting, helps to hold the cells together in a single straight line to form a uniform and consistent layer. Okay!
So getting back to the types of epithelia, in order to study them, let's take a simple example. Imagine this to be a basement membrane. Now depending upon the functions, let's classify them.
So let's say the first function is filtration. What kind of structure should be present according to you? Yes!
It needs to be a very flat surface. So this type of epithelium is referred to as simple squamous epithelium. Now let's take up the next function that is absorption and secretion.
For this, obviously we would need a larger surface area, right? Which is why we have these tall pillar-like cells on the basement membrane making up the columnar epithelium. Now at times, we need the strength or support along with the larger surface area. In this case, we slightly change the structure to cube-like cells and form the cuboidal epithelium.
Lastly, we have certain organs that need specialized secretions. So in such cases, we need to modify a few cells that would perform secretion of specific chemicals like hormones or enzymes. These are called the gland cells And the epithelium consisting of such type of cells is called the glandular epithelium. Well, this was about the epithelial tissue in short. Now let's meet up in the next video where we will discuss these four types of epithelia.