00:00Hello everyone, this is Megan from Kenhub and welcome to another anatomy tutorial.
00:06In today's tutorial we will be looking at the mucosa and the muscle layers of the stomach.
00:11When we're discussing these structures, we're going to be discussing them as they are seen
00:15with the naked eye or macroscopically. We're not going to use histological slides or a microscope.
00:22So let's begin with a complete view of the stomach.
00:25Here we can see the stomach connecting to the esophagus and duodenum. We can also see its
00:32internal surface and the folds which are called rugae. In the next illustration we can see the
00:37muscular layers of the stomach but we'll cover these later on in the tutorial.
00:42So the stomach is a muscular bag that expands to accommodate ingested food. The stomach connects
00:48the esophagus and the small intestine. It's found in the epigastric, umbilical and left hypochondriac
00:55regions of the abdomen. The stomach can be subdivided into four main parts. The cardiac part, the fundus,
01:04the gastric body and the pyloric part. The structure of the stomach is similar to the rest of the GI tract
01:12and is composed of mucosa, submucosa and a muscular layer. I'll talk a bit more about these layers later
01:19on in the tutorial. When we look at the stomach from an anterior view, like in this illustration,
01:26we can see the esophagus is the most superior structure. It connects the stomach with the upper
01:31alimentary tract. The esophagus is a long fibromuscular tube that connects the pharynx to the stomach.
01:39It passes through the superior and inferior posterior sections of the mediastinum.
01:44The esophagus then enters the abdominal cavity through the esophageal hiatus of the diaphragm
01:50at approximately the level of the T10 vertebra. Here we can see the inferior portion of the esophagus
01:57that connects to the stomach. The esophagus is supplied by the esophageal branches of the thoracic
02:03aorta. It's also supplied by the bronchial arteries and the ascending branches of the left gastric artery.
02:10The venous drainage is provided by small vessels returning blood to the asagous and hemiasagous
02:18veins and by the esophageal branches to the left gastric vein. The innervation of the esophagus is
02:25complex but it is mainly supplied by the vagus nerves and sympathetic trunks. The terminal end of
02:32the esophagus connects to the cardiac part of the stomach forming the esophageal stomach junction.
02:38Here the stratified squamous epithelium of the esophagus abruptly changes into simple columnar
02:45mucus secreting gastric epithelium of the stomach. In the next image we can see the internal structure
02:52of the stomach, we can see the rugae that I mentioned earlier and we can see the cardia
02:56highlighted in green. The fundus is the most superior dome-like part of the stomach formed by
03:03the upper curvature. It lies in the upper left hypochondriac region of the abdomen just beneath
03:09the diaphragm. It is filled with gas and is separated from the cardia by the cardiac incisera or the
03:15cardiac notch. The cardiac notch is the groove you can see here. The gastric glands in the mucosa of the
03:23fundus of the stomach also contain mucus neck cells, parietal cells, chief cells and enteroendocrine cells.
03:33Again we can see the inner structure of the stomach and we can see the fundus highlighted in green here.
03:39The body of the stomach or the gastric body is the largest part of the stomach. We can see it here
03:45highlighted in green. It forms the lesser curvature superiorly and the greater curvature inferiorly.
03:52This central portion of the stomach is situated between the fundus and cardiac part of the stomach
03:58and the pylorus. The next portion of the stomach I'm going to cover is the pyloric part. The pyloric
04:05antrum is the initial section of the pyloric part of the stomach. It is situated near the inferior margin
04:12of the stomach and is proximal to the pyloric sphincter. The pyloric part of the stomach starts at
04:18the angular notch here. During peristalsis it may temporarily be partially or completely closed off
04:25from the rest of the stomach. The most distal segment of the pyloric part of the stomach is the
04:31pyloric canal. The pyloric canal is approximately two to three centimeters long and is situated between
04:39the pyloric antrum and the pyloric orifice. It is the terminal part of the stomach.
04:45In the next illustration we can see the pyloric sphincter here highlighted in green. It is a band
04:52of smooth muscle that controls the flow of partially digested foot from the stomach into the small
04:58intestine. Now that we have covered the different parts of the stomach let's move on and cover some of
05:03the layers of this organ. As I've mentioned before the stomach is composed of three layers. The innermost
05:10layer is the mucosa followed by a submucosa and most externally a muscular layer. The muscular layer
05:18consists of three layers. A longitudinal layer, a circular layer and an oblique muscle layer.
05:27The longitudinal layer of the muscular coat is the outermost muscular layer.
05:32We can see that these muscle fibers are situated on the greater and lesser curvatures of the stomach.
05:39Now we've looked at the longitudinal muscle layer let's move on to the circular muscle layer.
05:44It is the middle muscular layer of the stomach and consists of circular muscle fibers.
05:50This layer of the circular muscle is concentric to the longitudinal axis of the stomach and forms the
05:55thick muscular layer at the pylorus which we know as the pyloric sphincter.
06:00The oblique layer of muscle fibers of the stomach is the innermost layer of the muscular layer
06:08and is responsible for creating the motion that churns and breaks down food in the stomach.
06:12It performs more forceful contractions at the fundus of the stomach.
06:18In this image we can see the oblique layer highlighted in green.
06:23Before we move on to the next part of this tutorial, I just want to show you that the longitudinal layer
06:29of muscle fibers continues into the duodenum, the next part of the GI tract.
06:34Here in the illustration you can see this longitudinal layer of muscle fibers
06:39which plays a crucial role in peristaltic movements.
06:42So now let's open up the stomach and see some of the internal features of this organ.
06:48The first part that we see here is the gastric canal, which is found along the lesser curvature
06:54of the stomach in the body of the stomach. It is a channel formed by the longitudinal mucosal folds.
07:01These gastric folds, which I've mentioned in previous slides, are also known as gastric rugae.
07:07They are formed by the mucosa of the stomach. They provide the stomach with an increased surface area
07:13for nutrient absorption. These mucosal folds stretch when food enters the stomach.
07:18This means the stomach is able to increase in volume without increasing the pressure inside the stomach.
07:24Another structure we can see when we look at the open stomach is the pyloric orifice.
07:30This is located at the end of the pyloric canal and marks the junction between the stomach and the duodenum.
07:36The pyloric canal is surrounded by the pyloric sphincter muscle.
07:40The pyloric sphincter marks the end of the stomach and the entrance to the duodenum.
07:45This sphincter is a strong band of circular muscle that reinforces the end of the stomach.
07:51Before we finish this tutorial, let's look at this structure highlighted in green here.
07:56It is not part of the stomach, but is closely related to it. It is the superior part of the duodenum,
08:02or the first part of the duodenum. The duodenum is a c-shaped loop that makes up the proximal
08:08part of the small intestine. It is adjacent to the head of the pancreas and is retroperitoneal,
08:14except for the very first portion of it. The duodenum is part of the small intestine and connects the
08:20stomach to the jejunum. There are four anatomical parts to it, the superior section, the descending
08:27section, the horizontal section and the ascending section. In this image we see the superior section
08:34of the duodenum. It contains a functional dilation known as the ampulla. The duodenum receives partially
08:41digested food from the stomach and plays a vital role in the chemical digestion of food.
08:47This prepares the bolus of food for absorption further on in the small intestine.
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