Hello everyone welcome back to my channel in this session I will be dealing with the topic diaphragm many of you have asked me to do a session on this because though it is very easy it is the most confusing one so when we talk about diaphragm we know there are many different types of diaphragm in the human body starting with the iris diaphragm the diaphragm of the oral cavity then we have the pelvic diaphragm but when we say simply diaphragm it is the chief muscle of respiration which separates the thoracic cavity from the abdominal cavity so before moving on to the development of diaphragm we should know at least some of the parts of the diaphragm so that it will be easy for you to understand the developmental sources and how each part of it is formed So in most of the textbooks we have seen a diagram like this. So some of you might have confused what is this view actually. So usually we have the diaphragm like this isn't it?
You have the thoracic cavity above and you have the abdominal cavity below. So the diaphragm will be like this. So anteriorly you have the sternum and posteriorly you have the vertebra. So if you just flip it like this.
This is the view. Okay, so if you just flip the diaphragm like this and if you are viewing like this, this is the view. This is the diagram which you will be coming across in most of the textbooks. That is why I am giving you an orientation like this.
So if you flip it like this, here comes the sternum. Then you have the vertebra here and these are the Thank you. ribs and what are the chief parts of the diaphragm you have a central tendon here central tendon then you have the major muscular portion then you have three major structures passing through the diaphragm they are the inferior vena cava esophagus and the aorta and you have the crura these are the crura right and left cruda.
So, diaphragm can be considered as a musculotendinous organ. Okay, so now we will move on to the development of diaphragm. So, the development of diaphragm is actually discussed under four main sources.
Let us see first which are the four main sources of development. The first one is septum transversum. septum transversum.
The second one is dorsal mesentery of esophagus. Third one is pleuroperitoneal membrane. And the fourth one is the mesoderm of the lateral body wall.
So when you are asked to mention about the developmental sources of diaphragm, you have to mention all these four points. The septum transversum, the dorsal mesentery of esophagus, then you have the pleuroperitoneal membrane and then you have the lateral body wall. So let's see one by one how are they contributing to the development of the diaphragm proper. So this is the body wall you can see this is the ventral aspect and this is the dorsal aspect that is the reason why we are having the vertebra here isn't it the dorsal aspect you have the vertebra and this is the ventral aspect then you can see a semicircular ventral growth from the ventral body wall and this growth is known as septum transversal. Okay, so this is known as septum transversum and this septum transversum, so here this portion is known as the septum transversum and we can see that the septum transversum actually separates.
Here you have the pericardial cavity and you have the peritoneal cavity below. So it is the septum transversum. which is seen on the ventral aspect and we can see that in the beginning the dorsal aspect of the septum transversal is a free border only the ventral aspect is attached the dorsal aspect is free and why is it free or what is the free border for me So at this point I would like to add one more point. You have the pleural cavity above and you have the peritoneal cavity below and there is a connection between the pleural cavity and the peritoneal cavity that is known as pleuroperitoneal canal. pleuroperitoneal canal so this cavity is the pleuroperitoneal canal pleuro peritoneal canal so you can see that just dorsal to the septum transverse there is a large cavity that is known as pleuroperitoneal canal and in course of development we can see a membrane Starting to close this defect.
So before I mention about the pleuroperitoneal membrane, we will just see one important structure. This is known as the dorsal mesentery of esophagus. dorsal mesentery of esophagus. So this portion you can consider it as an anteromedian portion.
Anteriorly you have the septum transversum and the medial portion almost you have the dorsal mesentery of esophagus. So these are the two important portions which are seen in the anterior and median portion and on either side of the dorsal mesentery of esophagus you have the canals that is the pleuroperitoneal canal on either side paired pleuroperitoneal canals. Now this membrane is the pleuroperitoneal membrane.
So this pardosal border of the septum transversum is actually forming a boundary of pleuroperitoneal canal. So we can see that this pleuroperitoneal membrane is actually coming closer to septum transversum and the dorsal mesentery and finally this bridges the gap that is it closes the pleuroperitoneal canal so that it separates the pleural cavity from peritoneal cavity so this dotted thing is the pleuroperitoneal membrane. So we discussed about septum transversum as a ventral growth. The dorsal border of septum transversum is free border which is forming a boundary of the pleuroperitoneal canal on either side. In the median portion you have the dorsal masonry of the esophagus containing the esophagus and later what happens is there is a growth of pleuroperitoneal membrane which actually separates the pleural cavity from the peritoneal cavity.
So at this point we haven't mentioned about the fourth contribution that is the mesoderm from the lateral body wall. All the three components have come the septum transversum the first one then you have the dorsal mesentery in the median plane then you have the pleuroperitoneal membrane all these three we have mentioned. So these three will be having a major contribution in the development of diaphragm during fetal period.
So towards the end of the fetal period, we can see that there is another mesodermal prolongation from the lateral body wall. And this will actually what encroaches towards the median plane and what happens is this pleuroperitoneal membrane will be now having only a very small contribution in adult diaphragm. The remaining portion will be actually filled with the mesoderm from the lateral body wall.
So that point you have to keep in mind. So pleural peritoneal membrane will be seen as a big thing contributing to the development of diaphragm in fetal period but in later course of development that is in adult diaphragm the major contribution is from in the posterior aspect is mainly from the lateral body wall the mesoderm of the lateral body wall and the pleural peritoneal membrane will be having only a very minor contribution. So, this is the adult diaphragm.
You can see this only this portion of the adult diaphragm is having a contribution from the pleuroperitoneal membrane whereas the rest of it is mainly contributed by the mesoderm of the lateral body wall. So, all the four components are over. Now, at this point I would like to mention one important structure. We have mentioned the two kruda the right kruda and the left the right crest and the left crest together you call it as crura of diaphragm. So the crura of diaphragm are developed from the myoblast.
You have the myoblast invading into the dorsal mucinry of esophagus. This is the dorsal mucinry of esophagus which mainly suspends the esophagus. So on to the dorsal mucinry of esophagus you have the myoblast cells invading and that will result in the formation of the right and left crust of diaphragm.
So the septum transversum is actually contributing to the formation of central tendon of diaphragm. Then you have the right and left crura which are developed from the myoblast invading the dorsal masonry of esophagus and the remaining portion of the diaphragm is having a major contribution from the mesoderm of the larynx. natural body wall. So this is the fetal diaphragm.
You can see the fetal diaphragm the in the center you have the septum transverse and on either side you can see the pleuroperitoneal membrane which is having a major contribution but when it comes to the adult What happens is you have the septum transversum but the pleuroperitoneal membrane is actually having a minor contribution that is what we have shown here and the major contribution you can see it as the mesoderm from the lateral body wall. So that is again one important thing you have to remember. Then along with the development we can also discuss about the nerve supply of diaphragm. So initially the septum transversum was seated in the cervical region and it was seen in relation with the cervical somites.
So the cervical segments corresponding are C3, C4 and C5. So that was the initial position of septum transversum in fetal period and later what happened is with the cranial the head fold and the descent of the heart what happened is the septum transversum came from the cervical region to the thoracic region and it is now in the adult period it is now lying between T7 to T12 so that is the extent of the diaphragm from T7 to T12. So what about the nerve supply of diaphragm? In the initial period since it was lying in the cervical region then and there itself it got the nerve supply from the c3 c4 and c5 cervical spinal segments and that is actually our phrenic nerve so the phrenic nerve is the nerve which is supplying the diaphragm muscular portion of the diaphragm and it is derived from c3 c4 and c5 because in the initial period of development it was seated in the cervical region but later in course of time it has descended down with the head folding and with the descent of the heart Now we have seen that though we say that the septum transversum is having a contribution the major contribution is also coming from the mesoderm of the lateral body wall. That is the reason why the sensory supply to the diaphragm is coming from the lower intercostal nerves.
So the lower intercostal nerves are actually supplying giving the sensory supply to the diaphragm whereas the muscular portion the motor part is coming from the phrenic nerve which is derived from C3, C4 and C5 due to its presence in the cervical region during the fetal period. So, these are the major four segments from which the diaphragm is developed. The septum transversum, the dorsal masonry of esophagus, the pleuroperitoneal membrane which separates the pleural cavity and peritoneal cavity and this is having a major contribution in the fetal period and the fourth one is the mesoderm of the lateral body wall. which is having a major contribution in adult period. So this point you have to keep in mind pleuroperitoneal membrane having a major contribution in fetal period and the mesoderm of the lateral body wall having a major contribution in adult period.
Now the septum transversum is mainly giving rise to the central tendon of typhrum then you have the crura of typhrum again formed from the dorsal mesentery of esophagus which is caused by the invasion of myoblasts into the dorsal masonry then the remaining portion we have discussed depending upon the fetal period and adult period you have it from the pleuroperitoneal membrane and from the mesoderm of the lateral body wall. Now at this point I would like to discuss some of the applied aspects which are favorite question for the examiners. The first one and the most important dreaded complication is congenital diaphragmatic hernia. So diaphragmatic hernia means there will be a defect in the diaphragm so usually we see the diaphragm as two domes isn't it just below the lungs you have two domes on either side and sometimes there will be a defect in the diaphragm and so what happens the contents of the abdomen will be actually entering into the thoracic cavity so what will happen if the contents of the abdomen enters into the thoracic cavity there won't be any place for the lung so there will be hypoplasia of the lung so that is a dreaded complication so on which side you get this defect congenital diaphragmatic hernia it is said that it is seen on the left side the congenital diaphragmatic hernia is most commonly seen on the left side and the reason is When the pleural peritoneum membrane starts to close on either side on the right and left side the right side closes first then only the left side. So it is a left side which fuses later.
That is the reason why you have a defect on the left side more common than on the right side and that defect is known as Bogdallic hernia. The Conchital Diaphragmatic Hernia is in that condition is known as Bogdallic Hernia. The next one is Retrosternal Diaphragmatic Hernia. What do you mean by that?
Sometimes what happens is there will be a defect in the anterior portion that is between the sternum and ribs there will be a defect in this portion of the diaphragm so again the result is the same that is the contents of the abdomen will be herniating into the thoracic cavity but the defect is in the anterior portion behind the sternum so that is why it is known as retro sternal or on either side of the sternum when it is coming from the when when the defects are in close relation with the ribs so then you can call it as parasternal so that type of hernia through this foramen is known as morgagnian hernia or hernia through the foramen of morgagni the third common variant or common commonest condition is congenital hiatal hernia so hiatus meaning means an opening in the anywhere in the body you call it as hiatus so if you if you call Hiatus in the diaphragm that is diaphragmatic hiatus and you know that there are mainly three structures piercing the diaphragm. One is the vena cava, then you have the esophagus, then you have the aorta. So usually what happens in congenital hiatal hernia is the opening of the esophagus will be larger. Okay, so the opening for the esophagus will be larger. So what happens is again through that opening the esophagus will try to drag the stomach which is lying down.
okay because the opening is large enough to drag the stomach upwards so that condition is known as congenital hiatal hernia through the hiatus the structure below is herniating so usually it is said that the congenital hiatal hernia is not that common compared to the rest of the abnormalities but what happens is in course of time there will be a larger hiatus but in course of time the patient will be presenting as acquired hiatus hernia. So acquired hiatus hernia usually will have a larger hiatus at birth but at that time it won't be presenting as hiatal hernia. It will be presenting as hiatal hernia only in later period and then we usually call it as acquired hiatal hernia. And the next important condition which you have come across is event ration of diaphragm.
So event ration of diaphragm congenital diaphragmatic hernia more or less looks alike because the symptoms and severity everything is similar what is the reason for that so what happens in event duration of diaphragm is there is no defect as such when you look at the diaphragm that is there is diaphragm in congenital diaphragmatic hernia there is a defect in the diaphragm that is a part of diaphragm is missing but in eventration of diaphragm there is no defect in the diaphragm but usually what happens is one half of the diaphragm will be thinned out without any muscular component it will be just membranous and again it is more commonly seen on the left side so what happens is the contents of the abdominal cavity will be pushing to the thoracic cavity as in case of congenital diaphragmatic hernia but it will be having a wrapper that is it will be covered by a thin membranous diaphragm. It won't be muscular portion. So, it is just equal to a defect in the diaphragm.
So, that is what is meant by eventration of diaphragm. So, eventration of diaphragm and congenital diaphragmatic hernia. Both are having more or less common symptoms. The reason is the contents of the abdominal cavity are coming into the thoracic cavity but in congenital diaphragmatic hernia you have a hole in the diaphragm through which the contents are herniating but whereas in eventuation of diaphragm there is no hole in the diaphragm but that part of the diaphragm is thinned out as a membrane so that it is not no longer able to hold the contents down.
That is it is just acting like a membrane and it is again more commonly seen on the left side. So these are the most common abnormalities which usually come across in case of development of diaphragm. Talking about the genetics of development of diaphragm, it is said that many genes on the long arm of chromosome 15 is said to have a vital role in the development of diaphragm. So all these points can be asked in one way or the other way.
when you attempt any entrance exams or for university exams. So please keep all these things in your mind so that you can very beautifully write a short note on diaphragm. So this is all about diaphragm in a nutshell. Please do leave your comments if you find it useful and those who haven't subscribed, please do subscribe so that I will get motivated to do future videos. Thank you.
Thanks for watching.