الرحيم الرحمن الله بسم

First of all the way in which the subjects will be written is announced as following: Oral physiology and head & neck anatomy will be written by

our Malaysian colleagues. Dental anatomy and microbiology will be written by Arabian

females. The rest of the subjects will be written by our other

colleagues.

Then our C.R announced that you can find our writing lectures on www.mytoothy.com and a day after they will be in "jam3eye"

After dr.ashraf welcomed us he said that he will not be happy when the students keep talking during the lecture, and our dr. will be ready to answer our head & neck anatomy questions.

Oral histology course is 3 credit hours ; 2 credit hours for the theoretical material and 1 credit hour for the practical material, that means 65% of our exam Qs will be theoretical Qs and 35% for slide Qs.In contrast to med courses, the dent courses have midterm and final exams with 40%, 60% respectively.There is 10% out of 40% of midterm exam related to the blank book and online quizzes by using e-learning.

The course lectures or theoretical parts cover the whole field of oral and maxillofacial histology and embryology and these include the different stages of odontogenesis which the process that include how the teeth and their parts are formed.The other topics which this theoritical part will cover are on the syllabus on e-learning.

Regarding the practical part of this course, it will be in the form of slides, so instead of going to labs, the Dr. will view the whole slides in the same hall, and it isn't necessary to view slides in each lecture.Our text book is:" ORAL ANATOMY ,HISTOLOGY AND EMBRYOLOGY"By B.K.B . Bercoritz ,G.R.holland and B.JMoxham.Its edition is three, but actually students could have also the fourth edition.If you are hesitative to buy this book, you are not forced to ,but the book strengthen your knowledge and you can use it as a reference.BUT there will be 5% of the Qs directly from the material that out Dr. will not mention which is found in the book.Unfortunately, the student can't easily score high mark in this course because of its long topics, but it isn't impossible if we make suitable effort, and the Dr. will be sympathetic by adding extra marks.BUT the case in other courses are not as same as oral histology case because you can easily score high mark enshalla.Most of the lectures will be found in the book, and the others will be from the lecture notes only to avoid disturbance.Remember try not to exceed the absence limit ( the absence limit is two lectures),otherwise you will not be allowed to enter the following exams.There is DVD which will be published soon has the needed microscopic slides which will be viewed as you proximately see them under microscope, because you are in need to sketch, identify the land marks at cellular levels and other Qs.

Again and again please don't contact with the Dr. by his private phone number, you can do so by his own e-mail or at his office hours.

Unfortunately, this lecture isn't presented in our text book because it is written by referring to more than one reference.You are responsible about extra notes which are mentioned in the lecture.Then our doctor asked us if we studied any topic related to embryology and we voted NO.Although this course name is oral histology, it is not proper to call it oral histology instead of that we call it oral histology and embryology.We know that HISTOLOGY means the knowledge that related to the structure of cells, tissues and organs.

Oral histology: the science that deals with the structure of oral cavity and it also includes oral embryology because this science includes both of structure and development. Oral embryology: the science that related to development of different cells and tissues that related to teeth and other oral structures.

Dr.ashraf started the lecture by skipping more than one slide or in other words leaving them to our self-reading because the Dr. assumed that we learnt a lot about these topics in general histology. So the Dr. quickly recovered human body, cell structure and function (each cellular organelle has its own function ,for example; endoplasmic reticulum is responsible about protein synthesis and ribosomes are responsible about enzyme synthesis),intra cellular material, cell division, genetic material, cell cycle in all its kinds and phases and finally the comparison between mitosis and meiosis , these all out lines cover slides (2-18)

Actually the lecture begins at slide # 19 which talks about general embryology.

Slide # 20There are three intra-uterine stages:

Pre embryonic stage (proliferative period). Embryonic stage. Fetal stage.

These stages are described as following:- Pre embryonic stage.

» this stage starts by the moment that the egg fuses with the sperm and the zygote is formed (first stage of fertilization)» the zygote gets implanted in the lining of the uterus (implantation process)» finally, the bilaminar embryonic disc is formed.So this stage starts by fertilization until two weeks, and it hasn't been named as an embryo yet.

- Embryonic stage:» this stage starts from the end of the 2nd week until the end of the 8th week» the embryonic is named so at this stage» the development of different types of tissues and the formation or development of organ systems occur at this stage.

-fetal stage:» this stage starts from the end of 8th week until the birth»there is increasing in fetus body weight and size.

Slide # 21 summarizes what happens:After the fertilization of unfertilized ovum the sperm could be seen inside it, then the zygote is formed.After that, the zygote starts to divide until reaching the lining of the uterus.

The zygote is already formed by many dividing cells to be implanted in the lining of the uterus,,,, this is general description of the whole process and the details as following: The zygote is the same size as the unfertilized ovum that means; fertilization process (fusing the sperm with the ovum)doesn't increase the unfertilized ovum size so this process keeps its size 0.1-0.2 mm.at the end of fertilization, the cleavage or mitotic division starts by two cells (each reproduced daughter cell is called blastomere) then four cells, etc………….

Note: note that in the embryonic stage there is formation and development in organ systems but in the fetal stage the systems already have been formed , so the general process is increasing in the weight and size without formation , so doctors ask pregnant ladies not to expose to x-ray especially at the first three months (embryonic stage), so after this proximate period pregnant ladies don't have to be much hazard from the exposure to x-ray.As a rule……pregnant ladies must not expose to x-ray during

pregnant period .

-the whole zygote will be called morula when the division reaches to 12-16 cells and that keeps the zygote as it is(0.1-0.2 mm)Each blastomere becomes smaller and smaller with each subsequent division without exceeding the original size.By forming blastocyst the cleavage stops.Before the implantation takes place, the blastocyst is formed (cyst means; cavity and blast means; an embryonic stage of development) that means there's a form of cavity in the blastocyst, so the blastocyst is named so because it has cyst.

? What do we mean by blastocoel?The blastocoel is the cyst itself.

Cyst = blastocoel = cavityBlastocyst is composed of 100-150 cells and also it has the same size as the zygote!Then the blastocyst starts to be surrounded by a membrane called zona pellucida.

?? What is the difference between inner cell mass and outer cell mass?

location Future development

Inner cell mass(embryo proper)

Inside the blastocyst

Making up the whole embryo

Outer cell mass (*future trophoblast)

Outer boundary Responsible about the embryo attachment

Future trophoblast: cells that form the attachment.So the actual cells that form the embryo are inner cell mass, and the outer cell mass is related to implantation and attachment.

Finally the implantation takes place.

In slides # 22 and 23, which talk about fertilization there is unneeded information you just need what does the Dr. say.

" this is just description of fertilization, you don't need more than the information that I provided, you will find some details here that are not needed, the details of fertilization are for your own reading, just the details which I talked about are needed"Then Dr. read the title of each slideCleavage………blastocyst……….implantation.

-pre-embryonic period: slide# 29 In this period the bilaminar embryo is formed.The zygote is already implanted in the lining of the uterus, and remember that there is a group of cells are divided into inner cell mass which is responsible about making the whole embryo and outer cell mass is responsible about the formation of attachment.This is the general description and the details as following :

- Inner cell mass will be arranged in two-layered disc ( bilaminar embryo)

- This two-layered disc is composed of two layers; top layer (embryonic epiblast) and bottom layer (embryonic hypoblast) they are the future ectoderm and endoderm respectively.

(embryonic hypoblast is yellow layer at the bottom as you can see in slide# 29) -this following table demonstrates the differences between embryonic epiblast and embryonic hypoblast:

Cell type Opposite cells Future development

Embryonic epiblast

Columnar cells

cytotrophoblat Future ectoderm

Embryonic hyoblast

Flattened cells

blastocoel Future endoderm

There is a word that I am not sure about describes embryonic hypoblast !!!

The embryo is formed by three layers: Ectoderm. Mesoderm. Endoderm.

These three layers are not formed at the same time, for example; mesoderm layer couldn't be seen at this stage.We conclude that mesoderm and ectoderm layers are formed firstly, and the third layer (mesoderm) becomes later on.

-these following structures are identified as following: Amniotic cavity: a cavity which lies between embryonic

epiblast and cytotrophoblast, which is filled by amniotic fluid, this fluid surrounds the embryo and fetus later on.

Exocoelomic membrane: membrane that lines the blastocoel, it's continuous with endoderm or hypoblast.

Primitive yolk sac (exocoelomic cavity): the development of blastocoel.Imagine that all of these changes occur, while the bilaminar embryo has the same as the ovum!!

Now you could note in slide# 30 these parts obviously:From the top layer to the bottom one:Ectoderm-amniotic cavity- primary yolk sac which started to divide to become secondary yolk sac-exocelomic membrane- endoderm."this formation isn’t important"

- Extra embryonic mesoderm from cytotrophoblast and forms secondary york sac and connecting stalks, and this actually established the placental circulation.

Extra embryonic mesoderm isn’t included; it is for your self-reading.

The following topics are important slides# 31,32:

First of all the terms in embryology are different from what anatomy has, for example: superior and inferior used in anatomy but cephalic and caudal in embryology.

embryonic period: Here, the embryo's age is two weeks and more. So what happen in this period?Look at this slide carefully, if we make a cut in the amniotic cavity and then we look superiorly we see something like what we see in pictures A,C,E in slide# 31. (we know that the amniotic cavity lies above ectoderm so when we make a cut you could see ectoderm layer ) So what is the layer that we could see here? It is the ectoderm. The cavity which we could note is the amniotic cavity which we make cut in. Could you notice that swelling in the cephalic end?This swelling is called prochordal plate and this swelling is important in the formation of the mouth.If you note again, the embryo has two ends; the cephalic end which lies near the future head and leads to the formation of the head and the caudal end which leads to the formation of another end of embryo. This swelling id due to slight thickening in underlying endoderm, so the thickening doesn't occur in ectoderm it occurs in endoderm.This plate produces a bulgy in ectoderm to indicate the head end and this plate becomes buccopharyngeal membrane.

So……what do we mean by buccopharyngeal membrane?

Firstly, we learnt in anatomy that oral cavity ends at the beginning of pharynx and there is a boundary between pharynx and oral cavity then there is esophagus.Buccopharyngeal membrane (oropharyngeal membrane) is a membrane that develops from prochodal plate and it separates the mouth from esophagus, when it erupts after 21 days it establishes the continuity between mouth and first GIT tract (pharynx).So before the buccopharyngeal membrane is named so, its old name is prochordal plate. There is another membrane which is called cloacal membrane at the caudal end but it isn’t important for us now. Let us talk about the intra- embryonic mesoderm : mesoderm layer appears from ectoderm after 17 days, so the ectoderm layer is the origin of mesoderm cells, and here it's called intra- embryonic mesoderm because this layer appears between ectoderm and endoderm that means , this layer separates the ectoderm from endoderm .If you return back to the last slide (31) you will find that if you make cross section you will see B,D,F pictures.As you see there is thickening in ectoderm extends to the midline and once they reach the midline they round up then they go down.So thickening in ectoderm is due to division and building up of cells until reaching the midline then they go down and spread between ectoderm and endoderm, by this process mesoderm is formed.

*mesoderm separates ectoderm and endoderm except in:

- Prochordal plate.- Notochord.- Cloacal membrane.

To memorize these three region that the mesoderm are not presented in, you can collect the first letter of

these three words in this short sentence " pay cash now " I think that it's an interesting way to memorize later.

Again, because of the formation and division of cells then rounding up then going down so they make depression at the midline so specific structures are formed. As you see in slide# 32 primitive node is presented at the cephalic end of primitive streak which is the midline, and the depression in the midline is called notochord …"Don't worry about it , it's just for your own reading"

At the end we conclude that germs have three layers; ectoderm, mesoderm and endoderm.

Finally, Why doesn't mesoderm layer separate ectoderm and endoderm in notochord??Notochordal process is a blind-ended tube that started from primitive node, notochord actually is a depression in which a tube has been formed to reach prochordal plate, so it separates the ectoderm and endoderm,, so there is no mesoderm at this region.And this notochordal process is the progenitor of backbone and vertebral column.Then Dr. gave us short rest then the topic was completed.

Thanks to Nada Nammas.Done by: Mays Jaradat.