hey guys my name is mean-ass and today I'm going to be talking about the embryological development of the lux and as usual I'm going to break it down very simply so that if you have no idea what is going on you will understand how the lung develops by the end of it and we're going to start in the beginning as always so that if you don't know anything about embryology not just about the lungs then you should get a grasp of what's going on we're going to begin at the blastula that's the ball of cells that's the result of fertilization with the sperm and the egg fused and they go down the uterine tube and then they implant onto the uterine wall and once implanted they undergo a process called gastrulation which turns the ball of cells in the middle there'll be three germ layers ectoderm mesoderm and endoderm and this is an oversimplification for this in blue we have the ectoderm the red is mesoderm and green is the endoderm and in this three steps you'll notice that the ectoderm pinches off and becomes a neural tube you'll notice the mesoderm differentiating into three parts and you'll notice the endoderm becoming a choose pinching off as well the mesoderm has three parts the paraxial mesoderm which becomes muscle the intermediate lizardom which becomes going on a kidney and the lateral plates the lateral plates there is a somatic mesoderm and a spanking mesoderm and how this has anything to do with the lungs is this so the first high-yield point is where does the lung come from in this picture the epithelial cells are made from gut tube endoderm and the cartilage muscle and connective tissue is from splanchnic mesoderm that's the first high point okay so this being a cross-section of the very early primitive fetus this way we're going to have a look at the fetus at four weeks in a sagittal section and you'll see it's all color code in green we have endoderm the GI T and you'll notice that the respiratory diverticulum is an outpouching of the GI T so at week four the lumbar appears and it's an aircraft outgrowth from the ventral or the front part of the GI t of the foregut okay that's the second high yield point if we just forget everything here and just focus down here this being in week four around sixteen days and now this is in about 25 days we have here the fogger it's color-coded in green and the respiratory diverticulum or the initial lung blood is a lung but is in blue so what happens is that tracheal esophageal ridges form and eventually pinch off the respiratory diverticulum from the fogger and during these phases there outpouching will also develop into bronchial buds where this is the land but these are poaching's are the bronchial buds they will form the trachea and these two will initially will become the right main bronchus and the left main bronchus and that's a good example over here at week five where we have a trickier the right main bronchus with its bronchial buds and the left main bronchus and his bronchial buds so just to recap lung comes from end odo or it's epithelial cells come from end odor from splenic masada we get connective tissue muscles and the cartilage and also splanchnic mesoderm makes spank spanking and somatic measure to make up both the visceral and parietal pleura respectively okay so let's have a look at week six over here we have a week six lung and then a week eight lung so you'll notice that with growth the lung tissue expands and fills this red which is color coded for mesoderm and the space in between here is called the pericardium pericardial peritoneal canal and the lab will grow quarterly and laterally so that means it'll grow down and out filling the cavity that it will that the body allows it to feel so it will continue to grow and as it grows the primary bronchi will form three secondary bronchi bronchi on the right and two secondary bronchi on the left and this is foreshadowing the different the lobes of the lung so we have three lobes on the right side and two lobes on the left side okay so from week five to week eight we have the lungs rapidly filling up the body cavity or the pericardial peritoneal cavity and it fills it up to the point where it's always stuck to the visceral pleura the visceral pleura is from splanchnic nezhoda and the parietal pleura the one on the outside is from somatic residue from lateral plates and so histologically we have here a terminal bronchial and this is the last point of the bronchial where there are no alveoli and over here we have a respiratory bronchioles with which actually has alveoli attached to it so initially it's all cuboidal epithelial cells surrounding everywhere including at the terminal sacs here the terminal sacs are just blind ended sacs that will become the alveolar and if you notice over here as it develops the blood cap of capillaries become migrated and invade the terminal sacs and as well you'll notice that there are squamous epithelial cells being made at the end where the capillaries are actually invading so the squamous epithelium also known as type 1 alveolar cells and they get thin so that gas exchange can happen okay the blood vessels invade so that oxygen can go in and then the carbon dioxide can come out with ventilation okay so as the lungs mature the vascular supply is increasing and also type 2 alveoli are beginning to produce surfactant before birth the lungs are filled with fluid and this fluid contains phosphor lipids proteins and surfactant as well as other proteins some of this fluid actually goes into the amnio where it acts on macrophages these macrophages migrate to the chorion and release interferon one beta which help to stimulate the production of prostaglandins and we know that prostaglandins actually stimulate uterine contractions and so we can say that there's some evidence that the fetus can actually signal the initiation of labor I think that that's very interesting also before birth some of this fluid is aspirated and that actually will help to define the muscles help to improve the respiratory muscles of the fetus for birth and when the baby is born most of these fluid is actually absorbed except for the surfactant which coats the lining of the lungs and helps to make a oxygenation and ventilation from lung expansion much easier because it reduces the surface tension finally let's talk about some of the things that could go wrong with the development of the lung namely esophageal atresia so essentially you can have three forms of this you can have a blind end and a fistula that connects the trachea to the distal esophagus you can have two blind ends or you can have a communication of the esophagus with the trickier but still have a hollow tube of a full esophagus going to the stomach thank you very much for watching and I appreciate the time you