Anatomy clinical correlates: Viscera of the gastrointestinal tract

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Introduction0:00–0:26

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!

Ulcers0:26–1:04

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.

Duodenal ulcers1:04–1:57

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.

Gastric ulcers1:57–2:32

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.

Gastric arterial supply2:32–3:13

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.

Gastric cancer3:13–3:44

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!

Quiz3:44–3:57

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.

Superior mesenteric artery syndrome3:57–5:54

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.

Identification of Appendix5:54–8:01

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.
For example, with retrocecal appendicitis, individuals may present with an iliopsoas sign, which is when pain appears during extension of the hip.
A more anterior placed appendix may cause localized sharp pain in the right lower quadrant. Finally, when the appendix lies in the pelvis, atypical pain below the McBurney Point may occur.
Individuals can also present with a positive obturator sign, which is when there’s pain on flexion and internal rotation of the hip as the appendix is in contact with the obturator internus muscle fascia, and is stretched and irritated during this maneuver.
Moving down our tubular pathway, let's look at a clinical condition affecting the vasculature of the large intestine. Remember that the GI tract is supplied by three major arteries: the celiac trunk, the superior mesenteric artery, and the inferior mesenteric artery.

Watershed regions and ischemia8:01–9:34

Now between these major arteries there are anatomical areas called watershed regions, which are anatomical regions supplied by the terminal branches of two major arteries.
In regards to the large intestine, its blood supply comes from the superior mesenteric artery and the inferior mesenteric artery, therefore any area that received blood supply from the terminal branches of both these vessels is considered a watershed region.
One watershed region is the splenic flexure, or left colic flexure, which receives blood from narrow terminal branches of the superior mesenteric artery and the inferior mesenteric artery.
Another watershed region is the rectosigmoid junction, which receives blood from narrow terminal branches of the inferior mesenteric artery and the superior rectal artery.
Because they are supplied by narrow terminal branches, these two areas are more prone to ischemia due to hypoperfusion, which can be the result of blockage due to atherosclerosis, emboli, or thrombi.
The main symptoms of colon ischemia includes mild to severe abdominal pain and cramping in the region where ischemia occurs, rectal bleeding, diarrhea, distension, and in severe cases shock and dehydration.

Sigmoid volvulus9:34–10:27

Next, let’s tackle sigmoid volvulus, which is when the sigmoid colon twists around its mesentery, leading to obstruction of its lumen, compression of blood supply and subsequent ischemia.
The sigmoid colon has a higher likelihood of volvulus due to its freedom of movement, and the risk of volvulus increases with a particularly long sigmoid colon with a narrow mesenteric attachment.
Symptoms of sigmoid volvulus have an insidious onset and include abdominal distention and progressive abdominal pain, and eventually signs of obstruction such as nausea and vomiting.
Now, on an x-ray, you can see a U-shaped distended sigmoid colon seen as a collection of gas, which can extend anywhere from the pelvis to the upper abdomen.
If you look closely, this kind of looks like a coffee bean, which is why it’s also called the coffee bean sign. Finally, let’s wrap up this video by talking about hemorrhoids, which is a term used to describe the dilation of veins in the rectal venous plexus.

Hemorrhoids10:27–12:20

These vessels may become swollen or inflamed, leading to what we refer to as internal hemorrhoids or external hemorrhoids.
Okay, now hemorrhoids result from the breakdown of the muscularis mucosa of the rectal wall, which allows rectal veins to prolapse through.
Hemorrhoids are classified into internal and external hemorrhoids based on their location to the pectinate or dentate line.
Internal hemorrhoids are located above the pectinate line and affect the internal venous plexus, which drains into the superior rectal veins.
External hemorrhoids, on the other hand, are below the pectinate line and affect the external venous plexus, which drains into the inferior rectal veins.
Due to their position above the pectinate line, internal hemorrhoids receive visceral innervation from the inferior hypogastric plexus and are not sensitive to pain, touch or temperature.
External hemorrhoids, however, receive somatic innervation from the inferior rectal nerve, a branch of the pudendal nerve, and are therefore sensitive to touch, temperature, and pain.
Both types of hemorrhoids are typically asymptomatic. Internal hemorrhoids can prolapse through the anal canal and become compressed, which may cause strangulation.
Alternatively, internal hemorrhoids may bleed resulting in painless visible bleeding coming from the rectum. External hemorrhoids can become inflamed, causing itching and discomfort, and due to the somatic innervation of external hemorrhoids they can be… a literal pain in the behind if they thrombose!
Hemorrhoids are often the result of increased intraabdominal pressure, and can result from chronic constipation, pregnancy, obesity, and increased straining on defecation.
Alright, as a quick recap. When duodenal or gastric ulcers perforate the anterior wall, that can cause a pneumoperitoneum, which is associated with free air under the diaphragm on an x-ray.

Review12:20–14:20

Posterior wall erosion of duodenal and gastric ulcers, as well as lesser curvature ulcers of the stomach, can cause gastrointestinal bleeding.
The fundus of the stomach is supplied by the short gastric arteries, which are prone to ischemia if there is a blockage to the splenic artery.
Next, signs of metastatic gastric cancer would be a left supraclavicular node enlargement, known as Virchow node, and periumbilical nodal enlargement, known as Sister Mary Joseph nodule.
Superior mesenteric artery syndrome is a rare cause of proximal intestinal obstruction where the third portion of the duodenum is compressed between the aorta and superior mesenteric artery.
During an appendectomy, the tenia coli can be used as a landmark to find the appendix. The position of the appendix can vary; it can lie behind the cecum; beneath the peritoneal covering of the cecum, in which case it’s often fused to the cecum or abdominal wall; or it can project inferiorly into the pelvis.
The watershed regions of the colon include the splenic flexure and the rectosigmoid junction and these regions are more prone to ischemia, due to the fact that their blood supply is provided by narrow terminal branches of the superior mesenteric artery and inferior mesenteric artery.
Sigmoid volvulus happens when the sigmoid colon twists around its mesentery, causing obstruction in the descending colon and it can cause the coffee bean sign on an x-ray.
Finally, hemorrhoidal disease is when the internal and external venous plexues of the anal canal become swollen. These include internal hemorrhoids, which are found above the pectinate line, and external hemorrhoids, which are found below the pectinate line.
Both are often asymptomatic, however external hemorrhoids may