In this video, we'll talk about the morphogenetic movements that are happening during the process of gastrulation. So here are a few key points regarding gastrulation. Gastrulation is all about coordinated movement of many cells and this movement happens throughout the embryo. Patterns of gastrulation vary throughout the animal kingdom and there are several types of core movement that can happen during gastrulation.
In this video, we are going to talk about that. So the possible movements that can occur during gastrulation phase are invagination, involution, ingression, delamination and epiboly. These five type of movement are the basic ABCDs of the gastrulation or morphogenetic movements.
So in this video we are going to break down on each of these movement and try to appreciate when they occur and how they occur. So before that let me tell you that Louis Valpert mentioned once that it's not birth, marriage or death but gastrulation is the most fascinating part of the life. So why gastrulation is so important and what really happens during gastrulation? So let me tell you briefly that during gastrulation a cell in the blastula can move their positions and they can obtain new neighbors and can move in a coordinated fashion. So it's a pretty complicated kind of phenomena.
So the first type of gastrulation movement that we are going to look at is invagination. As the name suggests there is something invaginating right. So invagination simply means enfoldings of a sheet of cells just like this animation.
You can see the yellow cells are invaginating inwards just like you are touching a rubber ball and there is a depression when it when you're poking it this movement is exactly similar to that so this kind of movement happens during c-archine endoderm formation so also this kind of movement can be found in amphioxus so when the amphioxus blastula is giving rise to the gastrula the Endoderm region invaginates inside and eventually forms the Archenteron so this is one of the another example the next movement is known as involution involution is the inward movement of an Expanding outer layer so that the new layer is now spread Internal to the external cell layer, okay? if you don't understand follow this particular yellow cells these yellow cells are actually generated from these green cells which are on the outer side when the outer side that means these green cells are dividing and increasing in number it is mo it is moving slowly slowly inwards just like these arrows and it is spreading just beneath this outer layer And this kind of movement is known as involution. Just for better understanding, let's look at this process with the help of animation.
So you can see how these yellow cells are involuting inside the green outer layer. Next movement is ingression. Ingression is a process by which individual cells move out from the surface into the interior of the embryo but before moving out of the layer it is it has to perform epithelial to mesenchymal transition if you don't know what is epithelial to mesenchymal transition i have a video on that so here you can see this yellow cell become mesenchymal and moving out from the layer of these green cells and this kind of movement is known as ingression let me tell you ingression is found in case of a vertebrate especially human embryonic development where the cells of the epiblast ingress and move inside the primitive streak and then move down and move away from the primitive streak.
In a cross section you can see this. So look at that particular dot in the cross section view. This cell is ingressing that means first it has undergone EMT or epithelial to mesenchymal transition.
So it became loose and now it is moving Towards the primitive streak now It's going down towards the primitive streak and now it's moving away from the primitive streak and it would become something else in the new Location now similar kind of movement or ingression kind of movement can be found during the CR chin Mesoderm development here you can see the red represents the mesoderm and the mesodermal cells are Ingressing inside the embryo the next kind of movement is delamination delamination is very similar to ingression but delamination results in splitting of one cellular sheet into a parallel sheet Now one difference between delamination and ingression is delamination occurs in a collective fashion. One cell doesn't move inside. It's a whole layer of cells that splits or move inside. So delamination is very important type of morphogenetic movement and then epibole is the last movement that we are going to talk about. Epibole one kind of movement where epithelial sheets are spreading as a unit so it's again a collective movement and it encloses the deeper layers of the embryo in this case you can see the yellow sheet is kind of like engulfing the green sheet of cells so this is known as epibole epibole can occur by cell division cell shape changes and several layers of cells that are intercollected and they can like split into smaller layers.
Now this kind of movement is very common in case of frog embryonic development. So in case of frogs, you can see the ectoderm, endoderm and mesoderm are labeled in three different colors. Now if you follow the arrows, you can see how this red ectoderm is slowly, slowly engulfing. the entire endoderm and this is what happens during ectoderm formation in amphibians and this is an example of epiboli.
So I hope this video was informative and short enough. In a different video we would talk about each of these movements and try to understand the molecular mechanisms that is governing this kind of coordinated movement. Please visit my Facebook and Instagram page for more flashcards and notes.
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