# The Peritoneum --- The **peritoneum** (para-tah-knee-um) is a [[serous membrane]] that lines the [[abdominopelvic cavity]]. The segments that line the cavity itself are called the **parietal peritoneum**, and the segments that line the organs are called the **visceral peritoneum**. The potential space between the parietal and visceral peritoneum is called the **peritoneal cavity**, which is filled with a serus fluid called the **peritoneal fluid**. A **mesentry** is a general term for and extension of the double-layered peritoneum that supports and stabalizes the intraperitoneal [[gastrointestinal tract|GI tract]] organs. They contain [[blood vessels|blood]] and [[lymphatic system|lymph]] vessels, and also nerves inbetween the two folds that supply the organs. Just like other serous membrane, mesenteres are sometimes named specifically for the organ they protect. ![[peritoneum.png]] ![[transverse peritoneum.png]] Not all organs in the abdominopelvic cavity are surrounded by visceral peritoneum, and these are called **retroperitoneal organs**. Retroperitoneal organs usually have one surface covered by the peritoneum, but are not surrounded by it. The [[pancreas]] and [[duodenum]] are two examples. Organs that *are* surrounded by visceral peritoneum are called **intraperitoneal organs**. ___