What’s a serous membrane?

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A serous membrane is a thin membrane that helps parts of the body move more easily and reduces friction between them. Also known as serosa, these membranes are found throughout the body, usually around organs. There are several medical conditions associated with the serous membrane, some of which can be life-threatening.
Features and location
The serosa consists of two layers of tissue with a thin layer of serous fluid in between. One layer is made up of mesothelium, which produces the fluid, while the other is made up of connective tissue, which attaches the membrane to other parts of the body and supplies blood and nerves to the epithelial layer. The serous fluid itself is a thin liquid that is normally pale yellow, but can become milky, dark yellow, or red in people with infections or other medical conditions.

Many places on the body have serosa, including the body cavities surrounding the heart, lungs, abdomen, and pelvic area. It is also found in the stomach, uterus, testicles and vagina. Depending on where the membrane is located in the body, it can be called in different ways: for example, the serous membrane around the heart is called the pericardium, while that around the lungs is called the pleura, and that which surrounds the testicles is called the tunica vaginalis.

Function

While all serosa are primarily used to reduce friction, their exact function differs slightly based on location. The pericardium, for example, facilitates the expansion and contraction of the heart as it beats, as well as protecting and keeping it in place. Likewise, the pleura makes it easier for the lungs to expand by reducing the friction between them and the surrounding tissues, but it also makes the outer layer of the lungs adhere to the surrounding tissue, which helps keep them from collapsing inward.

Related issues

Problems with a serous membrane can be related to the serous fluid or the two layers of tissue. An overproduction of fluid can cause serious problems, especially if enough fluid is produced to put pressure on a person’s organs. This is called an effusion when it occurs around the heart or lungs and ascites if it occurs in the peritoneum. All three can be life-threatening if not treated promptly and usually need to be treated by draining the fluid with a needle. The serous fluid can also be infected with bacteria or mixed with the blood due to a problem elsewhere in the body.

Another condition that affects the tissue layers of the serous membrane, rather than the fluid, is malignant mesothelioma. This is a cancer that most often affects the pleura, although it can affect any serosa. It is mostly associated with asbestos exposure and is generally very difficult to treat.

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