LO6 - Abdominal Wall

6. Describe the basic organization of the peritoneum and peritoneal cavity, including a few of the most clinically relevant mesenteries and ligaments.

The peritoneum, a serous membrane lining the abdominopelvic cavity, consists of two layers: visceral and parietal peritoneum. Parietal peritoneum lines the walls of the cavity, whereas visceral peritoneum covers viscera suspended within the cavity. Between the parietal and visceral peritoneum is a dynamic potential space, the peritoneal cavity.

Intraperitoneal v. Retroperitoneal

    • Intraperitoneal refers to viscera covered by visceral peritoneum and suspended within, but not inside the peritoneal cavity.
    • Retroperitoneal refers to organs located posterior to the peritoneum.
    • Structures may either be primary or secondary retroperitoneal, depending on their developmental history. A primary retroperitoneal structure (i.e. kidneys, inferior vena cava, aorta, proximal rectum, ureters, and suprarenal glands) develops and remains retroperitoneal, whereas secondary retroperitoneal structures (i.e. the 2nd and 3rd parts of the duodenum, the ascending and descending colon, and most of the pancreas) begin development intraperitoneal, but eventually are drawn retroperitoneal.

Mesentery

    • A mesentery is a double layer of peritoneum encasing fatty connective tissues and neurovasculature. It serves to attach intraperitoneal viscera to the body wall. Specific mesenteries are often given specific names based on location and often start with ‘meso.’
    • ‘The’ mesentery (of jejunum & ileum) anchors the majority of the small intestine to the posterior abdominal wall.
    • The transverse mesocolon is a double layer of peritoneum connecting the transverse colon to the posterior abdominal wall.

Omenta

    • Omenta are folds of peritoneum which bind viscera to other viscera, or to the abdominal wall. The omenta are derived from the dorsal and ventral mesogastria (mesenteries), which anchored the primitive gut tube to the abdominal wall.
    • The greater omentum is largely rooted on the stomach. It consists of several specialized peritoneal connections to viscera, such as the omental apron, a ‘free-hanging’ double layer of the gastrocolic ligament, which hangs inferiorly from the greater curvature of the stomach anterior to the jejunum and ileum, before looping back to the transverse colon.
    • The lesser omentum is composed of the continuous hepatoduodenal and hepatogastric ligaments. The hepatoduodenal ligament is located between the liver and duodenum. The portal triad (bile duct, hepatic artery proper, and portal vein) is conducted through this ligament.

Peritoneal fold v. Peritoneal ligament

    • A peritoneal fold is a reflection of parietal peritoneum on an abdominal wall, causing a visible, raised structure. These are often caused by fetal, obliterated vasculature or canals or vasculature and ducts (e.g. medial umbilical fold, lateral umbilical fold).
    • A peritoneal ligament is a double layer of peritoneum, connecting viscera with another viscera or viscera to an abdominal wall (e.g. falciform ligament, hepatoduodenal ligament).
    • The falciform ligament is a peritoneal ligament (reflection) between the anterior abdominal wall and the liver. This ligament surrounds the round ligament of the liver (the remnant of the umbilical vein).