Anatomy clinical correlates: Viscera of the gastrointestinal tract
Content Reviewers:Viviana Popa, MD, Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.)
The gastrointestinal tract runs from the mouth all the way to the anus and contains the esophagus, the stomach, the small and large intestine and the anus. All these structures, like any other part of our body, are prone to injury or disease.
This video will give you a better understanding of the anatomy of the GI tract and how it relates to the clinical conditions that affect them!
Let’s start by looking at gastric and duodenal ulcers, which are open lesions in the lining of the stomach or duodenum that lead to inflammation in the gastric or duodenal wall.
These are often associated with a specific stomach bacteria called H. Pylori, H.Pylori....Helicobacter Pylori.
Duodenal ulcers are more frequent than gastric ulcers and can be located anywhere along the duodenal wall, classically affecting either the anterior or posterior duodenal wall. If severe enough, ulcers can erode through the duodenal wall, which can cause perforation or gastrointestinal bleeding.
Anterior wall duodenal ulcers are more prone to perforation into the anterior abdominal cavity, and this can result in a pneumoperitoneum, because air from the gastrointestinal tract enters the abdominal cavity.
A classic finding on x-ray is free air under the diaphragm indicating a pneumoperitoneum. This can also result in peritonitis, because as duodenal contents leak into the abdominal cavity, they irritate the peritoneum.
Posterior wall duodenal ulcers can also cause perforation, but more frequently, they cause upper gastrointestinal bleeding.
That’s because the first part of the duodenum, called the duodenal bulb, is positioned directly anterior to the gastroduodenal artery, so an erosion of the posterior wall can also cause erosion into the gastroduodenal artery resulting in an upper gastrointestinal bleed.
Most gastric ulcers are located at the lesser curvature of the stomach, an area where both the left and right gastric artery can be found perfusing the stomach.
So, if a gastric ulcer erodes the lesser curvature, this can result in an upper gastrointestinal bleed. Gastric ulcers can also be located posteriorly, in which case they can erode through the stomach wall and into the pancreas.
In doing so, these ulcers can also erode the splenic artery, which lies along the upper border of the pancreas, resulting in severe bleeding into the peritoneal cavity.
Now, speaking of gastric blood supply, most of the stomach is well perfused with a rich anastomotic network, for example the lesser curvature receiving blood from both the right and left gastric artery.
The fundus of the stomach however, is mainly perfused by the short gastric arteries, which are branches of the splenic artery.
Unfortunately, these short gastric arteries have a poor anastomotic network, leaving the area they supply susceptible to ischemia following any blockage to the splenic artery.
Therefore, any potential blockage to the splenic artery such as atherosclerosis, emboli, or compression can result in ischemia to the fundus of the stomach.
To wrap up our discussion on stomach clinical correlates, let’s talk about gastric cancer. The most common type of gastric cancer is gastric adenocarcinoma, which is capable of aggressive local spread and metastasis.
The most common physical exam finding of metastasis in gastric cancer is an enlarged, palpable, sometimes even visible left supraclavicular node, also known as Virchow node. Metastasis may also spread to the periumbilical nodules, known as a Sister Mary Joseph nodule.
Time for a quick quiz! Where are GI ulcers often located? What happens if a duodenal ulcer perforates posteriorly?
Let’s switch gears and talk about some clinical correlates regarding the small and large intestine. First, there’s superior mesenteric artery syndrome, which is a rare cause of proximal intestinal obstruction, which is when the duodenum is compressed between the superior mesenteric artery and the aorta.
Anatomically, the third portion of the duodenum passes between the aorta and the superior mesenteric artery as it courses from right to left across the abdomen.
Typically, the duodenum crosses anteriorly to the aorta at the L3 vertebral level. The superior mesenteric artery arises from the anterior part of the aorta at the level of L1, and extends downwards into the mesentery as it goes on to supply the small and large intestines.
In most individuals, the angle between the superior mesenteric artery and the aorta is at about 45 degrees, allowing space for the duodenum to pass between them.
If this angle diminishes to less than 20 degrees, then the duodenum has the potential to become trapped between the superior mesenteric artery and the aorta, which causes compression of the duodenum leading to superior mesenteric artery syndrome.
Clinical presentation of superior mesenteric artery syndrome may present insidiously and are consistent with proximal small bowel obstruction.
This narrowing of the aortomesenteric angle can occur with any condition that reduces mesenteric fat. This is often associated with things that cause large weight loss, such as malignancy, eating disorders, malabsorption syndromes, burns or bariatric surgery.
Furthermore, significant anatomic changes can lead to this syndrome, such corrective scoliosis surgery. Symptoms of superior mesenteric artery syndrome can mimic those of bowel obstruction and include postprandial epigastric pain, early satiety and in more severe cases, nausea, bilious emesis and weight loss.
Next, let’s quickly go over some tips and tricks on how to identify the appendix during surgery. The appendix is normally located at the junction of the small and large intestine, roughly 2 centimeters below the ileocecal valve.
To remove the appendix, the three tenia coli are used as a landmark. The teniae coli begin distally as a continuous layer of longitudinal muscle that surrounds the rectum below the serosa.
At the rectosigmoid junction, this muscular layer forms 3 distinct longitudinal bands that can be seen on the external surface of the colon.
These three bands continue proximally along the colon where they converge at the root of the vermiform appendix, so by following these teniae coli the cecal base the appendix can be identified. When in doubt, search for the teniae coli!
Sticking with the appendix, recall that there is anatomical variation to the position of the appendix. The attachment of the appendix is constant to the base of the cecum, however the tip of the appendix can migrate.
The most common position is a retrocecal appendix, where the tip extends posterior to the cecum and extends superiorly towards the right colic flexure.
Other times, the appendix lies beneath the peritoneal covering of the cecum and in this case it’s often fused to the cecum or to the posterior abdominal wall.
The appendix may also project inferiorly into the pelvis. These variations can affect the clinical manifestations of appendicitis.
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