Anatomy of the Colon, Rectum, and Anus

Richard L. Drake

Jennifer M. Mcbride

Michelle D. Inkster

James S. Wu

Surgical Anatomy, properly understood, implies not merely relation of parts, but such an acquaintance of the position, function and relations of the structures entering into the formation of any region, as may assist in the diagnosis and treatment of the injuries and diseases occurring in it; or in certain cases to judge how far operative interference is warrantable, and guide us, if it be, in planning and performing the operation.

Edward Bellamy, FRCS

The Student’s Guide to Surgical Anatomy, 1885

Attributed to Professor Spence

The intestinal tract begins at the duodenum and ends at the anus.

Peritoneum

The intestines are enveloped variably in peritoneum (Fig. 1-1). In his 1903 syllabus of surgical anatomy, Thomas describes the peritoneum as follows:

Peritoneum. The peritoneum is a closed serous sac, having no external communication, except in the female through the Fallopian tubes. It intervenes between the abdominal wall and the viscera, which are intraperitoneal only in the sense that they invaginate the posterior layer. The viscera are held in position by the folds of peritoneum or mesenteries thus formed. They may have a complete covering, except where the two layers of these folds meet, as in the case of the ileum and jejunum, the transverse colon, stomach and spleen. Often a viscus is only partly covered, as in the case of the kidney, bladder, ascending and descending colon.

Small Intestine

The small intestine consists of the duodenum, jejunum, and ileum (Fig. 1-2) and is open, except at its beginning (pylorus) and at its end (ileocecal valve).

FIGURE 1-1 ▪ The peritoneum is a sac that covers the intestines, either completely or partially. Except for its first part, the duodenum is retroperitoneal. The jejunum, ileum, transverse colon, and sigmoid colon are covered by peritoneum and suspended on a mesentery. The ascending colon, the descending colon, and the rectum are partly covered. (Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2019. All Rights Reserved.)

FIGURE 1-2 ▪ The small intestine is shown with its location relative to the large intestine. (Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2019. All Rights Reserved.)

Duodenum

The term “duodenum” is derived from the Latin duodenum digitorum (space of 12 digits) because its length is about the breadth of 12 fingerbreadths. The duodenum is the first section of the small intestine and, except for the first part, is retroperitoneal. It is C-shaped and formed around the head of the pancreas (Fig. 1-3).

FIGURE 1-3 ▪ The duodenum is located in close proximity to the pancreas, hepatobiliary system, vena cava, portal vein, vertebral column, aorta, superior mesenteric vessels, urinary system, and the colon. (Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2019. All Rights Reserved.)

The duodenum is divided into four parts (Fig. 1-4) as follows.

The superior or first part begins at the pyloric sphincter and ends in the area of the neck of the gallbladder. It lies anterior to the bile duct, gastroduodenal artery, portal vein, and inferior vena cava.
The descending or second part passes from the neck of the gallbladder to the inferior edge of vertebra L3. It is anterior to the medial portion of the right kidney and just lateral to the head of the pancreas. Associated with this part are the major duodenal papilla and minor duodenal papilla.
The inferior or third part passes anterior to the inferior vena cava, abdominal aorta, and vertebral column, and its anterior surface is crossed by the superior mesenteric artery and vein.
The ascending or fourth part is to the left of the abdominal aorta and passes upward, ending at the duodenojejunal junction. The ligament of Treitz (suspensory muscle/ligament of the duodenum) is associated with this junction.

FIGURE 1-4 ▪ The duodenum and its relationship to the biliary system, vena cava, portal vein, and superior mesenteric artery/vein. The pancreas has been removed. (Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2019. All Rights Reserved.)

The arterial supply to the duodenum is from the gastroduodenal artery, the supraduodenal artery, duodenal branches from the anterior and posterior superior pancreaticoduodenal arteries, duodenal branches from the anterior and posterior inferior pancreaticoduodenal arteries, and the first jejunal branch from the superior mesenteric artery (Fig. 1-5).

Jejunum and Ileum

The jejunum and the ileum are completely covered by peritoneum and connected to the posterior abdominal wall by a mesentery. They travel from the left upper quadrant to the right lower quadrant.

Jejunum

The word “jejunum” is derived from the Latin ieiunum or “empty” because it is often found empty on dissections. The jejunum follows the duodenum and represents about two-fifths of the small intestine. The arterial supply to this portion of the small intestine consists of jejunal arteries that are branches of the superior mesenteric artery (Fig. 1-6). Venous drainage is via the superior mesenteric vein.

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