Understanding the peritoneum

Reed Mitchell

As a first year medical student, I could not understand the peritoneum. The shiny smooth membrane covering the surface of the bowel, the back of the abdomen, and the inside of the abdominal wall is one thing, and two, at the same time. The visceral peritoneum covers the bowel and abdominal organs and the parietal peritoneum covers the abdominal wall. But these two parts are not distinct; they are one; they are continuous. Like the universe, if you start in one spot and travel completely around, never leaving the peritoneum, you will end up where you started.

The visceral and parietal surfaces of the peritoneum touch each other, but never fuse. Between them lies a __potential space__ containing a thin film of proteinaceous fluid lubricating the two surfaces. Every day during the fall of 1981 I asked my professor to explain __potential space.__ "Imagine the inside of a pillow case without the pillow," he said. The pillow case is flattened and laid over the abdominal organs, and then pushed into the rounded corners between liver, spleen, pancreas, bowel, fat, and blood vessels. The outside of the pillow case is fused to the connective tissue at the back of the abdomen, the organs, including the entire length of the small and large bowel, and the abdominal wall. Inside the pillow case is the peritoneal cavity. The abdominal organs reside inside the abdomen, but outside the peritoneal cavity. One of these pillow cases also covers each lung and the heart, creating the pleural spaces and the pericardium.

In health, the peritoneal cavity is as described above. With ovarian cancer it may be filled with cancer cells suspended in thick amber, bloody fluid. In liver disease or heart failure it may contain ascites–thin fluid that leaks out of the blood vessels serving the bowel. If this all makes perfect sense to you and you are not a physician, then __wow__, you are smarter than I am–or maybe it is because I explained it to you so well! I am no dummy. I was runner-up for the anatomy prize for first year medical students at Duke in 1981.

My problem was that I hated to memorize; I wanted to understand. Forty years later, my weakness has become my strength. Explaining complex topics by breaking them down to smaller, simpler concepts is my forte.

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