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Retroperitoneal organs are the organs in the body found behind the membranous structure of the abdominal cavity known as the peritoneum. These can be divided into primary and secondary retroperitoneal structures, with primary organs including the kidneys, bladder, ureter, rectum and uterus. In addition, the inferior vena cava and the aorta are considered primary organs. Secondary structures include the duodenum, pancreas and large intestine, with the exception of the sigmoid and transverse colon. These organs technically develop within the peritoneum, but become partially pushed back behind the membrane during embryonic development.
The peritoneum is a mucus lined structure that supports the majority of the organs in the abdominal cavity. It also aids in the transmission of blood and other nutrients to and from these organs. Retroperitoneal organs are not supported by this structure and are located between it and the solid abdominal wall. The retroperitoneal space is not clearly defined since it has no anatomical structures to mark its boundaries. Organs in this space are responsible for functions of the digestive, circulatory, urinary and reproductive systems.
The kidneys, bladder and ureter are retroperitoneal organs that perform vital functions in the urological system. They filter waste products in the blood and control the amount of water in the body. The rectum is the final portion of the large intestine and acts as a temporary storage site for solid waste before it is eliminated from the body. Found only in females, the uterus is responsible for providing the site for the implantation of a fertilized egg and the development of a growing fetus. Circulatory vessels known as the inferior vena cava and the aorta carry blood to and from the heart.
Secondary retroperitoneal organs originally form within the mesentery of the abdominal cavity, but are gradually forced back behind the peritoneum during fetal development. They may still protrude slightly through the membrane and thus are not considered truly retroperitoneal. These organs are part of the digestive system. The first part of the small intestine is called the duodenum, which begins the process of chemical digestion. While the pancreas produces enzymes that help to break down food products, the large intestine performs the majority of mechanical digestion by squeezing food and absorbing key nutrients.
All these organs are typically stationary and can be far more difficult to locate and manipulate surgically. Diseases of these organs tend to be serious, because the symptoms are often unspecific or appear only after the condition has entered its advanced stage. A common issue in this area is known as retroperitoneal fibrosis, in which one or more masses appear in the space and impede organ function.