In this video, we're going to focus on endocytosis and how endocytosis allows entry into the cell. And so the "en" in endocytosis is going to be very helpful to remind you about what it does, and that's because endocytosis is defined as macromolecule engulfment by the cell membrane allowing for entry into the cell via a lipid vesicle. And so you can see the "en" in endocytosis is for the "en" in engulfment and the "en" in entry. And so the big idea here is that molecules are going to be brought into the cell with endocytosis. Now, really, there are 3 main types of endocytosis that you all should know.
The first type is phagocytosis. Now phagocytosis is when a large solid material is being taken into the cell via endocytosis. And because it is a solid material, it's commonly known as cell eating. Now the second type of endocytosis that you all should know is pinocytosis. And pinocytosis is defined as when a small liquid material is being taken into the cell by endocytosis.
And because the materials are liquid, it's commonly known as cell drinking. And then the third and final type of endocytosis that you all should know is receptor-mediated endocytosis. And really, receptor-mediated endocytosis is just a special form of pinocytosis, and that's why we have this little indentation here to show that, hey, receptor-mediated endocytosis is just a special type of pinocytosis. And it says here it's a specific form of pinocytosis that uses receptor proteins. So let's take a look at our image down below to get a better understanding of these ideas.
So, on the far left over here, notice that we're showing you the first type of endocytosis, phagocytosis. And so notice that the outside of the cell is over here and the inside of the cell is over here, and notice that a bacterium is being brought into the cell here and when it's brought into the cell, it ends up inside of a lipid vesicle. And recall, vesicles are just these little membrane bubbles, and it will bring in these large solid materials such as the bacteria here. Now moving on, pinocytosis is over here in the middle, and notice that it is, the outside is over here and the inside of the cell is over here, and so these small liquid materials are being brought into the cell via a lipid vesicle. And so this is pinocytosis or cellular drinking.
Now the final type of endocytosis that you all should know is receptor-mediated endocytosis, which is really just a form of pinocytosis, so cellular drinking. So you can see the same blue molecules being brought in as pinocytosis. But the real difference is that receptor-mediated endocytosis uses these orange receptors that you can see embedded in the membrane at these positions here. And so, the receptors are proteins that have a specific binding attraction to these blue liquid, molecules. And then, of course, because it's a form of endocytosis, it's going to be brought into the cell in a lipid vessel.
And so the big idea here is that receptor-mediated endocytosis uses these receptors, these orange receptors. And so this here concludes our introduction to endocytosis and how endocytosis, the "en," is going to remind you that it allows for entry into the cell. And so we'll be able to talk about exocytosis in our next video. So I'll see you all there.