Hi everybody, my name is Andre and welcome to Med School EU. In today's lecture we are going to talk about the anatomy of the digestive system. So I want to break down the digestive system into two parts because there's a lot involved in terms of anatomy and there's a lot involved in terms of physiology. So in this first part we're going to talk about particularly the anatomy. and then a little bit about the accessory organs like the liver and the pancreas.
And the main focus is going to be anatomy. The next topic in the next video, we are going to talk about the second part of the digestive system, and that would be the function of each of these anatomical structures. And the first thing I wanted to talk about is, of course, how the food enters and what are the anatomical structures associated with the upper.
part of the digestive system. Now the food is going to enter through the mouth of course and in the oral cavity we're going to have several structures that are associated with it so let's put up some labels. Here we go the top of the mouth here at the very back and the top of the mouth is going to be the uvula involved with throat.
Now that would be the tongue the label that's right there. And there's other structures that make up the oral cavity. More predominant one is the hard plate at the top and the soft plate that's further towards the back of the mouth.
The next structure is going to be the pharynx right here. And we've got three salivary glands that release saliva inside our mouth, which is the first enzymes that come out of in terms of. the digestion because in the mouth we're going to have primarily mechanical digestion but we're also going to have some chemical digestion through the release of saliva because it does have some enzymes and that will be discussed in greater detail in the next lecture but here we're just going to label the three glands that we have.
We have the parotid gland that's the biggest gland that's kind of in the back and on the sides of the mouth and that would be parotid. The next gland that's closer to be under the tongue and that would be called sublingual. And the final one that would be under the chin and that one's called submandibular. So I just picked out some of the main structures associated with the mouth and the oral cavity and that would contribute towards the digestive system.
And the last one here is the esophagus. Moving past the esophagus, let's talk about the lower digestive tract. And it's going to contain lots and lots of different labels, as you can see here. But once we get to the bottom of it, it will be quite clear what's what.
So first, it's going to enter the stomach. Now, of course, this big one right here, one of our biggest organs in the body, is the liver. Now, this little sac sticking out of the hepatic duct of the liver is called the gallbladder.
And the yellow structure in the back here is called the pancreas. So liver, gallbladder, pancreas are called the accessory organs. And with these accessory organs, we're going to talk about their role in the digestive system just briefly in this lecture.
And most likely, we are going to discuss their specific roles in more detail in the next one when we talk about the physiology of digestion. And the label here that basically the vein that passes through the pancreas is called the pancreatic duct. And the veins that pass through liver to the gallbladder and to the pancreas, this whole thing that is connected here is called the common bile duct. Now the structure that's coming off right from the stomach, so the food is going to go through the stomach and... The rest of the structure is going to move down into the small intestine.
The small intestine is made up of three parts. The first part is called the duodenum. Now past the duodenum, it's going to move into the jejunum.
And finally, the last label here, the last part of the small intestine is called the ileum. So moving along from these small intestine, the food is now going to be passed on from the ileum to the cecum. So the cecum is the beginning of the large intestine, also known as the colon. And we're going to make some of the labels of the colon. First, the next part that enters where the food proceeds is going to be the ascending colon.
Then the one going across is called the transverse colon. Now if we're moving down, so the fold that goes down on the other side of the stomach, this one is going to be called the... descending colon.
So the order goes ascending first then transverse and then descending colon and then from the descending colon is going to go into several structures going along here. And the first one that's right there is called the rectum and finally the the fecal matter is going to exit through the anus. Now another little structure I wanted to talk about here and I wanted to provide a label for. is the part that's hanging off the C-Comb.
And it's called the appendix. So let's go through this again. And we will go through the order at which the food enters it.
So first, from the esophagus, the food is going to enter into the stomach through the sphincters. It's also going to exit the stomach through a sphincter. And it's going to enter the duodenum, which is part of the small intestine. The next part of the small intestine is going to be the jejunum.
And the final part of the small intestine will be the ileum. Now these accessory organs, they're typically going to act within the small intestine and the stomach. So their effects will be on the stomach and the small intestine in general, in terms of digestion.
I mean, liver's got plenty of other functions and the pancreas got plenty of other functions. But typically in terms of digestion, the accessory organs will act in the stomach and in the small intestine. So after the ileum... The food is now going to enter the large intestine at the ileocecal connection.
So at the cecum, then it's going to continue down to the colon. The first part of the colon is the ascending colon, then the transverse colon, then the descending colon, then it's going to enter into the rectum and exit through the anus. Next, I wanted to discuss the stomach anatomy in a little bit. more detail. So first off this part would be the esophagus and of course the food is going to enter through this esophageal sphincter.
So this would be the esophageal sphincter and this sphincter is designed so that the food can enter in a kind of stepwise manner in smaller quantities than simply just dumping it down and it's going to move down into the stomach. The stomach is composed of three different muscle groups. This would be called the greater curvature and over here is the lesser curvature. The top part of the stomach here is called the fundus and the stomach is going to have little folds because of the three muscle layers that are involved. The longitudinal muscle, the circular muscle, those three muscle layers that are going to be involved, they're going to form these folds and they're The folds are called rugae.
Now, of course, the middle here is called the body. So body of the stomach. The bottom here is called the pylorus.
And finally, the food is going to exit through the pyloric sphincter. And as we discussed previously, it's going to enter the duodenum. So these are generally the anatomical structures that you should be aware of.
And for the purposes of this course, Of course, the stomach anatomy can go into much, much greater detail than this. However, this would be the level that's expected of you to know in terms of high school material. I also wanted to talk about these two phenomenons called regurgitation and peristalsis, since they are involved in terms of the stomach and the esophagus. So regurgitation is the spitting up of food from the esophagus or the stomach without nausea.
So this is basically forceful contractions of the muscles, the smooth muscles that are within the esophagus or the stomach that is pushing the food backwards. Now in terms of peristalsis, that's something of the opposite because it's a series of muscle contractions. They're basically going to contract one at a time and it's again abdominal smooth muscles like the end esophagus.
or around the stomach that's going to push the food through to the sphincters. And these occur all around the digestive tract. And peristalsis is basically the phenomenon that has a series of muscle contractions, and they're designed in a way to force the food down the tract. Now, of course, peristalsis also exists as a phenomenon in other things, such as veins and other vasculature. However, just...
for the purposes of this video, we're talking about the digestive system. And peristalsis is when the smooth muscles of the digestive system, so the endothelial lining that has smooth muscles around it in the esophagus and especially in the stomach and all around the small intestines and the large intestines, all of these smooth muscles will be contracting in a manner that will push the food down the digestive tract instead of against it, which would be the opposite. that would be called regurgitation. Now I also wanted to talk about the basic functions of these accessory organs the liver gallbladder and the pancreas. So starting off with the liver.
The liver's function in terms of the digestion because it has so many other functions. But in terms of digestion, the main thing is to produce bile salts and bile. And the purpose of producing these bile and bile salts is for the emulsification of fats, because fats come in as large globules into the small intestine.
And in order to digest it, the liver will have to produce bile that will be released in a... crazy phenomenon that we're going to discuss in the next lecture and basically the bile and the bile salts will be able to emulsify divide the fats into smaller and smaller pieces kind of like a detergent that you use to wash your dishes and then the fat will be able to be absorbed by the cells and it's able to be processed and digested and absorbed by the small intestines Next talking about the gallbladder, its function is to primarily store the bile production that is happening in the liver. And it is also going to be able to release bile when there is food entering the stomach.
So the gallbladder is in control of storing the bile because of course liver will, it takes time to produce bile and you're not going to be able to release it immediately. So therefore the liver builds up the production of bile. that will be stored in this sack of gallbladder and then it will be released from the liver and the gallbladder in to the stomach and the small intestines in order to do its job. Now if we're talking about the pancreas, its main function is to secrete pancreatic juices.
And what this means is basically when food enters the stomach, the pancreas will be able to secrete pancreatic juices through a series of hormonal reactions that are going to happen that will be discussed in the next lecture. But for the purposes of this video, we're just going to talk about the pancreatic juice and what it's made up of. But it's basically a mixture of digestive enzymes, water, buffers like bicarbonate and electrolytes produced by the epithelial cells of the pancreas.
And the pancreatic juice drains through the main pancreatic duct, as we talked about earlier, the main pancreatic duct that enters the common bile duct and it's then going to be dumped into or secreted into the small intestine. And the main purpose of all of this is to buffer the stomach acid because the food coming out of the stomach is extremely acidic from the hydrochloric acid and therefore the buffers that are released within the pancreatic juice is able to buffer this acidity. that is more manageable for the small intestine.
It's not going to burn the small intestine. And also it's got these enzymes that are able to break down protein, fats, and carbohydrates. So this concludes our first lecture on the digestive system. Today we talked about the anatomy of the digestive system and a little bit about the accessory organs.
And in the next one, we are going to talk about the physiology of digestion.