In this video, we're going to focus on the fairings and the esophagus. So, these are passageways that connect the oral cavity with the stomach. So, it allows food to pass from the mouth to ultimately the stomach. Now, there are three main regions to the fairings. There's right next to the oral cavity, you have the oro fernx. Then you have the laryng ferings that then feeds into the esophagus. You have the epiglotus here that can actually shift downwards and when it shifts downward it kind of blocks off the trachea so that food items fluid items do not go into the trachea. There is a third component to the fairings shown right over here. So above the uvula this is known as the nasop fairings. This has absolutely no role in digestion just for air movement. So overall the fairings allows passage not only for food fluids but also for air. Now when we're looking at the tissue composition of the fairings it's going to be very similar to the oral cavity. Meaning you're going to have stratified squamus epithelio. you're going to have mucus producing glands that facilitate the movement of material down this tube. Now, in terms of musculature, you're primarily going to have skeletal muscle and there are two major layers of skeletal muscle. There's an inner what we call longitudinal layer and then an outer uh layer called feringal constrictors which are sort of like little fistlike uh structures that allow propelling the movement of material down into the stomach during the action of swallowing. So then we look at the esophagus. So the esophagus on its own is a fairly flat but it's muscular tube. So it's not uh rigidly kept open like the trachea. So it's a muscular tube that goes from the laryng ferings to the stomach. And near the interface with the stomach, it's going to pierce the diaphragm at a region known as the esophageal hiatus. So it joins the stomach and the area around this joining called the cardiac orifice is slightly thicker than all the other areas. And so it's very hard to tell anatomically but this slight thickening gives rise to the gastroosophageal sphincter or cardiac sphincter uh at the cardiac orifice. Now the sphincter prevents the acids from the stomach from regurgitating back into the esophagus. Now if this does happen, this leads to a condition called heartburn. So if the cardiac sphincter for example fails to completely constrict and block the movement of material up into the esophagus, then you get heartburn. So associated uh factors that can cause heartburn for example uh when you're over consuming food or drink uh obesity pregnancy and even running can sort of loosen that cardiac sphincter and allow for regurgitation of stomach acid that sort of erodess away the esophagus. Uh so this can also occur with a structural abnormality known as a hiatal hernia. This is when part of the stomach which ordinarily is inferior to the diaphragm actually appears above um the um esophageal hiatus. Uh and this is called a hiatal hernia. So if this is left untreated with ant so you're not treating it with ant acids eventually it will lead to an inflammation known as esophagitis uh and if it's recurring can lead to ulcers and ultimately lead to esophageal cancers. So when we look at the tissue composition of the esophagus we see the four tunics that we've discussed for the elementary canal. The esophageal mucosa is going to contain a stratified layer of squamus epithelial cells that can easily sloth off uh towards the intersection at the cardiac orifice. The the stratified layer actually becomes simple columnular. Um and then underlying that you have sub mucosa that has various glands that will secrete mucus that sort of keep the entire uh esophagus very sort of slippery. So that facilitates the movement of the food bolus down the esophagus. Now with regards to musculature within the muscularis externa, it depends on what region of the esophagus we are talking about. The most superior third is exclusively skeletal muscle. The middle third is going to be a half and half mixture of skeletal and smooth. And the most inferior part of the esophagus is going to be exclusively smooth muscle. Now lastly in place of the sarosa tunic we have a fibrous connective tissue which we've uh previously called the adventicia. Yeah.