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This section serves as an introduction to the basic anatomy of the abdomen.

The human gastrointestinal tract can be divided into upper and lower portions. All structures proximal to the ligament of Treitz can be thought of as the upper GI tract, while structures found distal to it are considered the lower GI tract. We will begin with axial sections depicting the upper abdomen, including the liver and stomach, and work inferiorly toward the pelvis (Figs. 5.1 through 5.9).

Fig. 5.1

(A) Cross section demonstrating relative anatomy of stomach, liver, aorta, and inferior vena cava. (B) This section offers a clearer view of the hepatic veins, which can be seen within the liver, draining into the inferior vena cava. Axial CT sections correlating with the same level of anatomical cut section.

Fig. 5.2

(A) Cross-sectional anatomy of stomach, liver, left and right portal veins, and spleen together with correlating axial CT section (B) correlating with the same level of anatomical cut section. The portal vein is formed by the superior mesenteric vein, inferior mesenteric vein, splenic vein, gastric veins, and cystic veins. The main portal vein splits into the right and left portal vein, then further branches into venules (along with a hepatic arteriole and bile duct, forming a portal triad), and ultimately terminating in the liver sinusoids. (C) Illustration demonstrating the portal vein ascending into the liver, and the hepatic vein joining the IVC. The segments of the liver are demonstrated as well. There are eight segments, each with its own arterial supply, venous drainage, and biliary outflow.

Fig. 5.3

(A) Cross section revealing location of gallbladder in relation to liver, stomach, and pancreatic body and tail. The gallbladder drains into the common hepatic duct via the cystic duct, which later joins the pancreatic duct to form the ampulla of Vater. This empties through the sphincter of Oddi into the duodenum. The portal vein is seen prior to its branching into left and right portal veins. Note the presence of the splenic flexure of the colon as well. (B) Similar cross section revealing anatomy of the pancreatic tail and body. Axial CT section correlating with the same level of anatomical cut section is seen below each pertinent illustration.

Fig. 5.4

The superior poles of the kidneys and the adrenal glands become visible, along with portions of the jejunum, as well as the transverse colon. The splenic vein, which will empty into the portal vein, is seen here also.

Fig. 5.5

More of the kidney is visible, along with ...

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