Parietal Peritoneum · What is it, Organs it Covers, and More

The parietal peritoneum refers to the outer layer of the peritoneum, which covers the abdomen and pelvic walls as well as the diaphragm. It consists of a single layer of mesothelial cells bound to fibrous tissue and is an embryological derivative of the mesoderm (i.e., the middle of the three germ layers identified during the early embryonic life).

The peritoneum is a thin membrane that lines the abdominopelvic cavity. It consists of two layers: the outermost parietal layer, referred to as the parietal peritoneum, which surrounds the abdomen and pelvis; and the inner visceral layer, which wraps around the abdominal organs. Between the two layers is a potential space that contains small amounts of serous fluid (about 50-100 mL), which consists of water, electrolytes, and immune cells (e.g., white blood cells). This fluid acts as a lubricant between the layers as well as a form of protection.

The parietal peritoneum is located in the abdomen, lining the walls of the abdominal and pelvic cavity. 

The parietal peritoneum covers the abdominal and pelvic walls as well as the diaphragm. As the outermost layer of the peritoneum, the parietal peritoneum demarcates an abdominopelvic cavity, also known as the peritoneal cavity, that contains almost every organ of the abdomen and pelvis. 

Depending on whether the organs are completely or partially covered by the peritoneum, they are classified as intraperitoneal or retroperitoneal organs. Intraperitoneal refers to organs or structures that are completely covered by the visceral peritoneum and include organs such as the liver, stomach, and transverse colon. On the other hand, retroperitoneal organs are organs that are not located within the peritoneal cavity and, therefore, are only partially covered by the parietal peritoneum. More specifically, only the anterior wall is covered by the parietal peritoneum. These organs are further classified as primary and secondary retroperitoneal organs depending on their position during development. The primary retroperitoneal organs develop and remain outside of the peritoneal cavity and include the adrenal glands, kidneys, and ureter as well as the abdominal aorta, inferior vena cava, and their respective branches. The secondary retroperitoneal organs, which initially develop intraperitoneal and become retroperitoneal structures throughout development, include the pancreas, the ascending and descending colon, and the distal part of the duodenum. 

The parietal peritoneum provides protection and support for the abdomen and its organs. This peritoneal layer covers the abdominal walls and acts as a lubricating surface, thereby decreasing the friction between the organs. Furthermore, the parietal peritoneum acts as a protective border against any pathogens (e.g., bacteria) that may penetrate the peritoneal cavity. Lastly, it covers and protects the blood vessels, nerves, and lymphatic vessels that supply the abdomen and pelvis. 

The peritoneum is determined as parietal and visceral based solely on the surface it covers. The intraperitoneal organs are covered by the visceral peritoneum. The visceral peritoneum forms various folds throughout the abdominal cavity. For example, the greater omentum is a large fold of visceral peritoneum that extends from the stomach downwards. Specifically, it extends from the greater curvature of the stomach to the transverse colon. Another fold of visceral peritoneum is the lesser omentum, which extends from lesser curvature of the stomach to the liver. There are additional ligaments composed of visceral peritoneum (i.e., the peritoneal ligaments) that connect the viscera to the abdominal wall and include the hepatogastric ligament. The parietal peritoneum, on the other hand, does not cover organs and instead covers the rest of the abdominopelvic wall and diaphragm. 

The parietal peritoneum has the same innervation as the abdominal wall that it lines. As such, pain from the parietal peritoneum is well localized. In addition to pain, the parietal peritoneum is sensitive to pressure, temperature, and laceration. Meanwhile, the nerve supply of the visceral peritoneum is the same as that of the organ it covers. Unlike the parietal peritoneum, pain from the visceral peritoneum is poorly localized. Therefore, pain from the visceral peritoneum is identified in the skin areas (i.e., dermatomes) that are supplied by the same sensory nerves that innervate the abdominal viscera. Additionally, the visceral peritoneum is only sensitive to extension and chemical irritation. 

The parietal peritoneum refers to the outer layer of the peritoneum, which covers the abdominal and pelvic walls as well as the diaphragm. The peritoneum consists of two layers: the parietal and visceral peritoneum. Even though most organs are covered by the visceral peritoneum, the anterior wall of retroperitoneal organs is covered by the parietal peritoneum.  The parietal peritoneum provides protection and support to the abdominal organs as well as the nerves, blood, and lymphatic vessels that supply the abdomen and pelvis. There is no difference between the parietal and visceral peritoneum except for where they are located and their sensitivities.