Prechordal Plate (Prochordal Plate) - Prechordal Mesoderm - Oropharyngeal membrane
ฝัง
- เผยแพร่เมื่อ 9 พ.ค. 2024
- In this video, Dr. Aizaz from MedicoVisual talks about; Prechordal plate [Prochordal plate]m it's development and functions
00:00 What is Prechordal Plate
08:10 Functions of Prechordal Plate
09:55 Review
12:17 3D Tour of Prechordal plate
Beginning the third week, at the cranial end of the embryo there is a circular thickening of cells present where only two germ layers i.e. Ectoderm and Endoderm are present with no mesoderm in between. This is the primordium of the future-mouth of the baby and thus is called the Oropharyngeal or buccopharyngeal membrane.
The endodermal layer [lower layer] of this oropharyngeal membrane consists of thickened columnar hypoblast cells. This patch of columnar hypoblast cells is called the Prechordal plate. So, at this stage, we can say the Prechordal plate is forming the endodermal layer of the oropharyngeal membrane. While no such special name is given to the ectodermal layer of the oropharyngeal membrane.
The prechordal plate is one of the most misunderstood structures of the embryo but I will try to untangle and simplify it as much as possible.
We have been discussing the ingression of cells through primitive streak, but what about the primitive node. As it turns out, cells ingress through this node as well. Pertaining to its round outline, as the cell ingress, they too maintain a columnar shape. The few initial cells that ingressed through the primitive node travel all the way from the node and reach to the prechordal plate and here they displace the earlier prechordal plate that was formed by the hypoblast, laterally. So, now the prechordal plate is formed by the cells that came from the primitive node. Still, not much change in the structure as it is still two-layered.
But later in the third week, an interesting thing happens. The so-called endodermal cells of the caudal most part of the prechordal plate proliferate, differentiate, and form a new layer between the caudal most part of the endoderm and caudal most part of the ectoderm of the oropharyngeal membrane. This layer is now called the prechordal mesoderm. Thus, some embryologists also like to call the cells of the prechordal plate as mesendodermal cells. [Mesoderm + Endoderm], as it forms both endodermal as well as mesodermal [prechordal mesoderm] layers. This Prechordal mesoderm later forms the mesodermal derivatives of the head region. Later, this Prechordal mesoderm will be enriched by contributions from the neural crest cells. Neural crest cells may sound alien to you, but do not worry, we will discuss more about that in later lectures.
It is interesting to note that as the caudal end became trilaminar now, after the formation of the prechordal mesoderm, the oropharyngeal membrane is now restricted to its cranial part that is still bilaminar. This bilaminar oropharyngeal membrane will later break down to form the opening of the mouth. Similarly, at the caudal end of the embryo, there is another bilaminar structure with no mesoderm in between, which is called a cloacal membrane.
Actually, the prechordal plate is not a static structure. It’s a dynamic structure that continues to change. There are some stages of its development.
At the end of the second and start of the third week, it’s a patch of thickened columnar cells with an overlying epiblast tightly stitched to it. Let’s call it “stage 1”
Then during the third week, as the cells from the primitive node intercalates into the earlier stage 1 version of the prechordal plate. Now let's call it the “stage 2” Prechordal plate and it too consists of overlying ectoderm of epiblast cells but the difference is that it is made of epiblast cells that came from the primitive node and not the hypoblast cells. The oropharyngeal membrane is still bilaminar.
Finally, at stage 3, prechordal mesoderm also appears at the caudal end, and now cranially the prechordal plate has only a layer overlying it while caudally it has two layers i.e total of 3 layers.
You get confused when in books you read that prechordal plate is a bilaminar structure and then suddenly, you see the prechordal mesoderm magically appearing in between this so-called “Bilaminar structure”. Some authors went miles-ahead to confuse my dear medical students by interchangeably using the two terms “Oropharyngeal membrane” and “Prechordal plate”.
Please note that the Prechordal plate is the endodermal layer of the oropharyngeal membrane at stage 1 and stage 2 but at stage 3 this prechordal plate only forms the cranial part of the endoderm of the oropharyngeal membrane. At this stage, the caudal end of the prechordal plate has nothing to with the oropharyngeal membrane. It is the precursor of the head and along with its overlying mesoderm and ectoderm will form the head of the baby later on. Furthermore, it is an important structure in the induction of the forebrain in overlying neuroectoderm.
Website: www.medicovisual.com
Email: draizaz@medicovisual.com
References
1. Schoenwolf GC, Larsen WJ. Larsen's human embryology. 4th ed., Thoroughly rev. and updated. Edinburgh: Churchill Livingstone; 2009.
2. Moore KL, Persaud TVN, Torchia MG. The developing human. Clinically oriented embryology / Keith L. Moore, T.V.N. (Vid) Persaud, Mark G. Torchia. Eleventh edition. Edinburgh: Elsevier; 2020.
3. Hyttel P. Essentials of domestic animal embryology. Edinburgh: Saunders; 2010.
4. Sadler TW. Langman's medical embryology. Fourteenth edition. Philadelphia: Wolters Kluwer; 2019.
May you get the same recognition and reward that you deserve , ❤
Thanks from all of my heart❤❤❤
You have no idea how fantastically helpful your videos have been, Dr. Aizaz. Embryology's been made so easy to study. Thank you so much, MedicoVisual!
You are very welcome
Thank you ☺️ from the lateral medial anterior and posterior sides of my heart 💓
Heart doesn’t have lateral surface 😝😉
Ur ascent is very much Pakistanian; well u succeeded in nailing in Mind ; love and respect from India
You are my life saver. I was having a difficult time comprehending this subject until finding your videos! Soooo fantastic thank you so much
Thank you very much! I spent a lot of time searching what prechordal plate actually is. This video clarified the term even more than I had expected. 👍🏻
Very understandable 3Dgarphic presentation and helpful for medical related persons especialy for first professional students.exellent presentation.
Thank you so much
Best explaination and visuals!!
Thank you!
I will contribute this man when I will earn my first salary after Graduation.
Thank you. Very good presentation. This shows the power of 3D object vs some blank 2D textbook images.
Glad you like it!
Thank you very much u made it so simple to understand....again thnqq for this animated lecture
Thank you so much for this video!!
Very useful video... Thank you so much 🔥🔥
Very detailed explanation!
Really...That's Amazing....🥰🥰
Great work!!!
Keep it up!!!
Thanks a lot!
U r doing great sir pls put more videos
OMG that was a game changer video for me ! ❤️
Thank you so much for your appreciation
Great job sir
Thank youu soo much
Thank you so much sir.
Wow...Very good explanation.
Thank you ❤️🔥
My pleasure 😊
very understandable video and nice explanation and thank you sir !
Most welcome!
Nice explanation ...
Thank you ..
You are welcome
YOU ARE MY HERO!!!
Thank you
Thank you so much
Awesome !! that’s the word
Suuuuuuper 👏👏👏👏👏
Thank you very very much
Excellent Lecture
Thanks
Excellent 👌
Thanks a lot 😊
Hi Dr. Aizaz, I wonder if the cloacal membrane is formed at the same time as the oropharyngeal membrane or it's formed in later development?
So so so superb 💕💕💕💕
Thank you so much
Thank you very much. Pls can you do a video on Fourth to Eighth week development of embryology?
Thank you for your comment and your interest in our embryology lectures. I appreciate your suggestion regarding a video on the development of embryology between the 4th and 8th weeks. I completely understand your request, and it's a valuable topic.
I'd like to let you know that I'm currently working on a system-based embryology lecture series, which will cover the foundational concepts you'll need to understand the events during the 4th to 8th weeks of development. The reason I'm focusing on the system-based approach is that these early events between 4th to 8th weeks of develop, essentially serve as a summary of the entire system-based embryology. Once we have a strong foundation, it will be much easier for both you and all our students to grasp these later stages and will also be easier for me to make this lecture.
So, I'll be covering the 4th to 8th-week development in detail once I have completed system-based Embryology.
Thank you for your patience and understanding. If you have any more questions or specific topics you'd like to see covered, please feel free to let me know. Your feedback is valuable to me.
Best regards,
Dr. Aizaz
@@MedicoVisual Okay Thank you very much
@@aclasswithrhee482 always welcome
Nice
Thanks
Ty
Thank you 🙏 very muchLove 💕💕💕💕💕💕🫠
It means prechordal plate has 3 layers?
Sir which software do you use for these 3D models?
Blender 3D
Sir among oropharyngeal membrane , primitive streak and cloacle membrane . Which form 1st, 2nd and last during week 3 sir ??? ( if you give which days they starting developing this structure , that helps alot sir )
I am not aware of the exact days.
@@MedicoVisual ok sir
Sir ,can you please tell that why did you call the endoderm
'hypoblast' although in previous lecture of gastrulation you told that there was formation of the three germ layer and hypoblast cells are replaced?
Hi. Please tell the timestamp.
@@MedicoVisual sir 1:46 ,but I understood now that you were explaining before the formation of the three germ layers.
@@garimajoshi6547 Yes. You are correct.
It depends upon what week you are referring to. If it is second week, and there are two layers, it should be called hypoblast. Otherwise, endoderm.
@@MedicoVisualAnd thanks a lot sir for these amazing lectures.
@@garimajoshi6547 you are most welcome
Sir u are saying after the formation of prechordal mesoderm the oropharyngeal membrane is limited to the bilaminar structure and prechordal plate is also reduced. So,technically it is still forming the whole endodermal layer of oropharyngeal membrane but u said it is only confined to cranial part of it,that's confusing.7:50 and 12:15 descriptive part
Oropharyngeal membrane, as per all of the embryology textbooks that I have gone through, is by definition, a two-layered structure. So as the Prechordal mesoderm is formed, the caudal part of oropharyngeal membrane is no more two-layered so by definition, we can not label it "Oropharyngeal membrane", only the cranial part is two layered and is deemed as oropharyngeal membrane. Regarding the prechordal plate, that too is by definition, the "Endodermal part of oropharyngeal membrane". So you are right, technically, prechordal plate is forming the endoderm of oropharyngeal membrane as well as the part caudal to it (that is underlying the prechordal mesoderm). But because we are saying that oropharyngeal membrane is restricted to cranial part only, we also say that prechordal part (i.e. endoderm of oropharyngeal membrane) is also restricted to cranial region only. This is not an absolute law. You will find a lot of discrepency among the books. Some books also consider the caudal region as the prechordal plate. If I remember correctly, Larsen's Embryology concur with the scheme I mentioned in this video. Unfortunately, there is no universally agreed upon naming convention here. So yes, it is very confusing. Nearly every book present it in its very own personal naming scheme, so things quickly get messy. I tried to squeeze the essence of this topic from 30+ books in this video.
@@MedicoVisual thank you so much sir for taking time to clarify my doubt.I am glad we have a teacher who clarifies every student doubt patiently.Once again thank you sir.
@@R.Bharathkumar2003 you are most welcome dear
Whyoro pharyngeal membrane has two layers
So that it can easily rupture to form the opening of the mouth.
Ty