Hello, everyone. In this lesson, we are going to be talking about the Basal Lamina. The Basal Lamina is a very important structure that is kind of like the foundation for your cells. It is especially important for your epithelial cells. Okay. So, the basal lamina acts as a thin but strong extracellular matrix under all types of cells, but is mainly found beneath epithelial cells. Epithelial cells are cells like your skin. They are also very important for the lining of your internal organs. For example, the lining of your digestive system is made of these specialized epithelial cells, and they have a very good, very important basal lamina structure. But it can be found in all types of tissues, including muscle, fat, and Schwann cells, which surround neurons. It is also found in neurons and kidney cells. In neurons, the basal lamina provides extra support that ensures that the synapse between two neurons is put together correctly. Also, in kidney cells, it creates an impermeable barrier inside the kidney cells so that waste products do not mix with the blood products. Now, the basal lamina is incredibly small. It is not 40 to 120 millimeters thick, as mentioned earlier, but rather 40 to 120 nanometers thick. This is only visible under a microscope. And speaking of that, we have this particular picture here of a cell, and we have the plasma membrane right here of this cell. The dark line you see under the plasma membrane line is the basal lamina. It is composed of very important proteins and molecules in the extracellular matrix, and it is used for structural support and as a foundation. Okay, everyone? Alright.
So now let's go down and talk about it a little bit more because the Basal Lamina has very specific proteins that create it. The Basal Lamina is composed of two main proteins. It is one of the main layers or main components of the basement membrane, but it is not the basement membrane itself. It is just a component and is the component of the basement membrane that is composed of these two proteins, which are glycoproteins that adhere to the plasma membrane of the cell.
The laminin proteins closely associate with and bind to the type 4 collagen proteins. These are utilized for strength for the basal lamina. We want this basal lamina to be part of the foundation that the cell can adhere to and stick itself to, so we want it to be strong. Collagen, which is actually the most common protein in your entire body, is used for that strength. There are many types of collagen. We are specifically talking about collagen type 4. Collagen makes up from 25 to 35% of all the proteins in your entire body, which is quite significant. The type 4 collagen is the strength, that foundation component, and the laminin is the binding component that binds it to the plasma membrane. As stated, type 4 collagen links with the laminin and other proteins to form a rope-like helix or rope-like matrix.
Now, this figure here is an illustration of what a laminin protein would look like. It has a particular structure which looks like a trident. Let me draw a quick example of what it would look like on these cells. So, let's draw some epithelial cells, which are unique because they are polarized cells. That means they have two unique sides. One side of the epithelial cells is the apical side, and the other side is the basal side. These two sides are separated by the tight junctions that form between the cells and have unique sets of proteins. The basal lamina is on the basal side of the epithelial cells. Let me start off by drawing these proteins that connect the laminin to the plasma membrane, which are the integrin proteins. From these integrin proteins, we will have our trident shape, which are the laminin proteins. Lastly, we have our collagen type 4 fibers binding to the laminin proteins, creating a unique matrix of collagen fibers which wind together like a rope or a trellis. This is the basic structure of the basal lamina. Remember that this is only one of the layers of the entire basement membrane. The extracellular matrix gets more complex than this, but just know that the basal lamina is very important for all cells, particularly in epithelial cells that line your skin and internal organs.
The basal lamina is made up of these laminin proteins that bind these collagen type 4 fibers to the actual epithelial cells, providing them a foundation and structure. Okay, guys. Let's go into some practice problems.
