In this video, we're going to examine the large intestine. So, let's first look at the unique features that are found in the large intestine. So, the first unique feature are the Tanaoli. These are three bands of longitudinal smooth muscle that is found in the muscularis layer. And because of the tone of the tanaoli, you form these pocket-like sacks called hostra. So, here's an example of a hostra. And my pen disappeared. Here we go. Right there. So, here's an example of a hostra. And based on the muscle tone, you form those little pockets. An additional attribute of the large intestine are these little fat-filled pouches shown right over here and actually throughout called epipolic appendages. uh other than their presence, we really don't understand what the function of these epiploic appendages are. Um then we have the five main regions of the large intestine. So we'll begin from the ilioal valve that is the juncture between the small intestine and the large intestine. And remember the large intestine is large not not due to length. It's actually significantly smaller in length than the small intestine. It has to do more with the diameter. So it's a much larger diameter uh intestine compared to the small intestine. So the first region after the ilioal valve is the seeum. Then we have a small little juncture here called the appendix. So the appendix is where we house um various bacteria. You also have malts. So those are mucosa associated lymphatic tissues u in addition to bacteria. So these bacteria are then used to recolonize the gut uh in case there's any um significant uh issue. So then we move on to the colon and then the colon is actually broken down into several main sections. The first section is the ascending colon. So you have the ascending colon. So the ascending colon uh is going to basically travel up the right side of the abdominal cavity up to about the level of the right kidney and then it makes this right-handed turn which we call the right collic or right hpatic flexure. And then we move on to the transverse colon. And the transverse colon is going to travel basically across the abdominal cavity uh directly anterior to the spleen roughly. It's going to then bend again 90° and we have our left collic or spleenic fixture or flexure excuse me. Uh and then we move down the descending colon. Okay. Okay. So, the descending colon then is going to go down the left side of the posterior abdominal wall. Um, and then inferiorly it's going to enter the pelvis. And then once it enters the pelvis, it's going to become sort of this Sshaped sigmoid colon. The Sshaped sigmoid, excuse me, the Sshaped sigmoid colon. Um then if we look at the colon in general, the colon in general is going to be uh retroparitinal. The exception is going to be the transverse and the sigmoid parts. These are both intraaritinal. Uh and it's going to be anchored by mezentary sheets. And so these two are going to be anchored by uh what we call misocolon. So the the misaloc colons shown right over here you have the transverse misalon um those are going to uh anchor to the abdominal wall. All right. So then we have the rectum. So the rectum is going to run pretty much right in front of the sacrum. uh and based on its location there. This is why uh through the rectum we can analyze for example any kind of issues in males for example with the prostate through the anterior rectal wall via a rectal exam. Now contrary to its name rectum actually means straight. Within the rectum, there are sort of three uh bends or curves. And these little uh curves or folds are known as rectal valves. And so it's these valves that prevent a person who passes gas from soiling themselves. So it stops the feces from being passed along with the gas. And lastly, we have the last segment of the large intestine, which is the rectum, excuse me, which is the uh anal canal. Uh, and if we look at the anal canal, there are two sphincters there just before the opening, which is the anus. There's the internal anal sphincter, which is composed of smooth muscle. And you have the external anal sphincter which is composed of skeletal muscle. So these are basically closing off uh the large intestine um unless somebody is defecating. So again just to review the seeum is the first part of the large intestine. The appendix is going to be including masses of lymphoid tissues and that's a storehouse for bacteria. And then the colon is composed of the ascending, the transverse, the descending and the sigmoid colon. So here we have a partic uh drawing just to show you the various mezzent. So the transverse misolon uh earlier we talked about the the liver being anchored to the lesser curvature of the stomach. That was the lesser um uh and then we have the greater um right over here. So recall that the greater um goes from the stomach in front of the small intestines and the transverse colon. Then we have the rectum. We've already mentioned the the rectal valves, the anal canal and the sphincters. So if we examine the uh region of the rectum and the anal canal, specifically the anal canal, you see these little columns here. And nestled in between the columns, you have these um anal sinuses. So there's a mucous secretion that occurs here and that facilitates the process of defecation. So if we examine the u microscopic anatomy of the large intestine and some adaptations, you have a thicker mucosa that consists of simple columnular cells. And this is going to be true throughout with the exception of the anal canal where you have stratified squamus epithelia to withstand abrasion. There are no circular folds. There are no villi. There are no digestive secretion. So there aren't any enzymes here. Uh there are however uh bacteria entic bacteria that can secrete things like vitamin B derivatives and we'll actually talk about that on the next slide. Uh you do have an overabundance of goblet cells. So you need the mucus to facilitate the movement um of the um I want to say fecal matter but you want to uh basically um facilitate its movement since the majority of the water has been sort of uh reabsorbed. Uh there are some venus plexuses in and around the anal canal and when these become inflamed uh they give rise to hemorrhoids. Now, we mentioned the bacterial flora. Uh, they're going to um colonize the colon. Remember, the appendix is sort of in a reservoir. They will synthesize several B complex vitamins as well as vitamin K. Vitamin K is especially important for the formation of various clot factors. These bacteria help to metabolize uh several molecules that we produce like mu mucin, heperin, hyuronic acid. Uh they facilitate the digestion of carbohydrates like for example cellulose which we don't have the enzymes to be able to digest. But a consequence of that digestion is that they can release irritating gases like dimethyl sulfide. Uh that's usually the smelly component of flattis. Uh could be carbon dioxide, could be [Music] methane. Um in addition to those bacterial uh flora, there are some viruses and prozzoa that are present in the intestines as well. Now you might ask well what's there to prevent the invasion of these entic microorganisms into uh the tissues outside of the large intestine. Well there's a very thick mucosal layer. Additionally there are components remember we talked about those malts. Uh basically we're sampling uh the various pathogens that are found in the uh large intestine presenting it to uh basically uh Tlymphosytes of the malt to initiate an immune response. We also release antibodies specifically class IgA. This is the antibbody that is usually found in secretions like tears uh that help to mediate responses to these microorganisms.