What is the Difference Between Intraperitoneal and Retroperitoneal

The main difference between intraperitoneal and retroperitoneal space is that organs in the intraperitoneal space develop inside the peritoneal cavity, whereas organs in the retroperitoneal space develop outside the peritoneal cavity. 

Intraperitoneal and retroperitoneal space are the two types of cavities that occur inside the abdominal cavity, separated by the peritoneum. Furthermore, some examples of intraperitoneal organs are esophagus, stomach, jejunum, ileum, caecum, appendix, transverse and sigmoid colon, while some retroperitoneal organs include the duodenum, pancreas, and ascending, descending and transverse colon. 

Key Areas Covered 

1. What is the Intraperitoneal Space
     – Definition, Development, Organs
2. What is the Retroperitoneal Space
     – Definition, Development, Organs
3. What are the Similarities Between Intraperitoneal and Retroperitoneal Space
     – Outline of Common Features
4. What is the Difference Between Intraperitoneal and Retroperitoneal Space
     – Comparison of Key Differences

Key Terms 

Abdominal Cavity, Intraperitoneal Space, Mobility, Organs, Peritoneum, Parietal Peritoneum, Retroperitoneal Spac, Visceral Peritoneum

What is the Intraperitoneal Space 

Intraperitoneal space is the cavity surrounded by the peritoneum. Usually, the peritoneum is the serous membrane which lines the abdominal cavity. Moreover, it contains a mesothelial tissue supported by a layer of connective tissue, which is thin. However, the main function of the peritoneum is to protect the organs in the abdomen. There are two layers of the peritoneum: parietal peritoneum and the visceral peritoneum. Generally, parietal peritoneum is the outer layer attached to the abdominal wall, while visceral peritoneum is the inner layer wrapped around the internal organs.

Figure 1: Location of the Peritoneum

Furthermore, the organs inside the intraperitoneal space are mobile. Some examples of intraperitoneal organs are the stomach, jejunum, ileum, cecum, appendix, transverse and sigmoid colon. Moreover, the first 5 cm of the duodenum and the fourth part of the duodenum, as well as the upper third of the rectum, occur in the intraperitoneal space. In addition, organs such as the liver, spleen, the tail of the pancreas, uterus, Fallopian tubes, ovaries, and the blood vessels of the gonads occur in the intraperitoneal space. 

What is the Retroperitoneal Space 

Retroperitoneal space is the cavity of the abdomen, occurring outside the peritoneum. Some organs that occur inside the retroperitoneal space are the rest of the duodenum, ascending and descending colon, and the middle third of the rectum. Also, the remainder of the pancreas, kidneys and adrenal glands, renal vessels, and the proximal uterus are the other organs in the retroperitoneal space. 

Figure 2: Vertical Disposition of the Peritoneum

Moreover, some organs such as kidneys are primary retroperitoneal organs as the complete organ is located in the retroperitoneal space. However, some organs are secondary retroperitoneal organs, which develop intraperitoneally and then become retroperitoneal organs. Some examples of secondary retroperitoneal organs are duodenum, rectum, etc. Furthermore, some organs such as the urinary bladder and the lower third of the rectum occur below the peritoneum. Therefore, they are known as subperitoneal organs. 

Similarities Between Intraperitoneal and Retroperitoneal Space 

• Intraperitoneal and retroperitoneal spaces are the two types of cavities that occur inside the abdomen. 
• Moreover, they are separated by two layers of peritoneum. 

Difference Between Intraperitoneal and Retroperitoneal Space 

Definition 

Intraperitoneal space refers to the space within the peritoneum, which is a thin transparent membrane, lining the abdominal cavity, while retroperitoneal space refers to the space occurring outside the peritoneum. Thus, this is the main difference between intraperitoneal and retroperitoneal space.

Types of Organs 

Some examples of intraperitoneal organs are esophagus, stomach, jejunum, ileum, caecum, appendix, transverse and the sigmoid colon. On the other hand, some retroperitoneal organs are the duodenum, pancreas, kidneys, ascending and descending colon. 

Mobility of Organs 

Moreover, the mobility of organs is another important difference between intraperitoneal and retroperitoneal space. Organs in the intraperitoneal space are generally mobile while organs in the retroperitoneal space are fixed into a location.  

Conclusion 

Intraperitoneal space is the space of the abdomen completely surrounded by the peritoneum. The organs inside the intraperitoneal space are mobile. Some examples of such organs are the stomach, esophagus, jejunum, ileum, and transverse and sigmoid colon. On the other hand, retroperitoneal space is the space which occurs outside the peritoneum. In contrast to intraperitoneal organs, the organs in this space are fixed to a particular location. For example, some retroperitoneal organs include duodenum, pancreas, kidney, ascending and descending colon, rectum, etc. Therefore, the main difference between intraperitoneal and retroperitoneal space is their position and the organs occur in them.   

References:

1. “Digestive System – The Peritoneum.” Boundless Anatomy and Physiology, Lumen, Available Here.

Image Courtesy:

1. “2403 The PeritoneumN” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia  
2. “Gray1035” By Henry Vandyke Carter – also Henry Gray (1918) Anatomy of the Human Body, Bartleby.com: Gray’s Anatomy, Plate 1035 (Public Domain) via Commons Wikimedia