Anatomy of the abdominal viscera: Blood supply of the foregut, midgut and hindgut

Transcript

The gastrointestinal tract is essentially a long tube extending from our mouth to our rectum. We rely on it to eat, break down our food and turn it into well…..you get the picture.

Due to its role in breakdown and absorption of nutrients, it is important to understand the different divisions and blood supply of the gastrointestinal tract.

The abdominal section of the gastrointestinal tract develops from three embryological structures called the primordial foregut, midgut and hindgut.

And, in turn, the foregut, midgut and hindgut all derive from the three embryonic germ layers: the endoderm, mesoderm and ectoderm.

The mesoderm is what forms the peritoneum, which either completely or partially lines the organs of the peritoneal cavity including the gastrointestinal tract.

It is important to understand these different embryological divisions as the foregut, midgut, and hindgut each have their own unique blood supply.

The foregut extends from the esophagus to the duodenum at the level of the major duodenal papilla where the pancreatic and common bile duct insert, and it consists of the esophagus, stomach, the proximal duodenum, as well as the liver, gallbladder, pancreas and spleen.

The midgut extends from the distal portion of the duodenum to the last third of the transverse colon. It consists of the distal duodenum, jejunum, ileum, cecum, appendix, ascending colon and proximal two thirds of the transverse colon.

Finally, the hindgut extends from the distal third of the transverse colon to the anal canal, above the pectinate line. It consists of the distal portion of the transverse colon, descending colon and sigmoid colon and rectum.

Now, remember that organs with the same embryologic origin share the same arterial supply, which primarily comes from the abdominal aorta and its single anterior branches: the celiac trunk for the foregut; the superior mesenteric artery for the midgut; and the inferior mesenteric artery for the hindgut.

The celiac trunk arises from the anterior wall of the abdominal aorta at the level of the twelfth thoracic vertebra and the aortic hiatus of the diaphragm.

It has a short course, going anteriorly and inferiorly for less than two centimeters before branching into three arteries: the left gastric, splenic and common hepatic artery. The left gastric artery ascends where it gives the esophageal branch, which supplies the distal portion of the esophagus.

Then it curves downwards along the lesser curvature and within the lesser omentum, giving small branches that supply the anterior and posterior walls of the stomach, and it also anastomoses with the right gastric artery.

The splenic artery travels to the left within the splenorenal ligament, a ligamentous connection between the spleen and left kidney, along the superior border of the pancreas, and it gives branches for the body of the pancreas, a posterior gastric branch, and a branch for the hilum of the spleen.

At the hilum of the spleen, the splenic artery gives short gastric arteries for the fundus of the stomach, and the left gastro-omental, or gastroepiploic, artery, that descends along the greater curvature of the stomach and supplies the walls adjacent to it.

Finally, the common hepatic artery goes towards the porta hepatis, which is a small but deep transverse fissure through which all the neurovascular structures of the liver pass.

The common hepatic artery separates into two main branches. The first branch is the gastroduodenal artery, that descends behind the first part of the duodenum and gives two more major branches.

First is the right gastro-omental artery, or gastroepiploic, which enters the greater omentum and passes along the greater curvature of the stomach, to supply its walls, and to anastomose with the left gastro-omental artery.

The second branch is the superior pancreaticoduodenal artery which soon divides into anterior and posterior branches that descend in front and behind the head of the pancreas, respectively.

These branches supply the head of the pancreas as well as the proximal part of the duodenum. After giving the gastroduodenal artery, the common hepatic artery continues as the hepatic artery proper, and on its way to the liver it gives the right gastric artery.

This artery runs along the lesser curvature of the stomach, supplying its walls and anastomosing with the left gastric artery. Finally, the hepatic artery proper branches into the left and right hepatic arteries which supply the liver.

The right hepatic artery also gives a branch called the cystic artery that goes within the hepatoduodenal ligament to supply the gallbladder and cystic duct.

So in essence, the celiac trunk, through its branches, supplies all the structures of the foregut! Let’s take a quick break and try to identify the main branches of the celiac trunk, as well as the regions that they supply.

Moving on down the abdominal aorta, at the level of the L1 vertebra and about one centimeter inferior to the celiac trunk is the superior mesenteric artery, or SMA.

The SMA branches from the abdominal aorta posterior to the neck of the pancreas, and as it travels inferiorly it emerges anteriorly and medially to the uncinate process of the pancreas.

It also crosses anterior to the left renal vein and the third part of the duodenum. The SMA runs through the layers of the mesentery and goes towards the ileocecal junction in the right lower quadrant, giving many intestinal branches along the way.

The first one is usually the inferior pancreaticoduodenal artery, that gives anterior and posterior branches to the duodenum and anastomosis with the anterior and posterior branches of the superior pancreaticoduodenal artery of the celiac trunk.

Then, the SMA gives around 15 to 18 intestinal branches to the jejunum and ileum. These adjacent intestinal branches form anastomoses with each other that look like loops, called the arterial arcades.

From these arcades arise many straight arteries, called the vasa recta, that supply and penetrate the intestines.

Branches for the jejunum have fewer and larger arcades with longer vasa recta, while the ileum has more arcades with shorter loops and shorter vasa recta.

Next, the SMA gives off the ileocolic artery which supplies the cecum and parts of the terminal ileum and ascending colon.

It also gives the appendicular artery that goes within the meso-appendix and supplies the appendix. The SMA also gives rise to the right colic artery that travels retroperitoneally to supply the ascending colon.

Lastly, the SMA gives off the middle colic artery which ascends retroperitoneally within the transverse mesocolon to supply the transverse colon.

Last but not least, going back to the abdominal aorta now, the inferior mesenteric artery, or IMA, arises at the level of the L3 vertebra, from the anterior wall of the abdominal aorta.