Serous Membrane

Serous Membrane Definition

The serous membrane, or serosal membrane, is a thin membrane that lines the internal body cavities and organs such as the heart, lungs, and abdominal cavity. The thin membrane is made up of mesothelium tissue which originates from the mesoderm. The serous membrane allows for frictionless movement in a number of vital organs.

There are a number of serous membranes in the body: the pericardium surrounds the heart and some of the blood vessels; the pleural membranes surround the lungs, and the peritoneal membrane surrounds the abdominal cavity and related organs. There are also serous membranes surrounding the testes (the tunica vaginalis).

Heart Wall
This figure depicts the pericardium that surrounds the heart.

Heart and lungs
This figure depicts the pericardium surrounding the heart and the pleura surrounding the lungs.

Serous Membrane Structure

The serous membrane is made of two layers of mesothelium joined by a layer of loose connective tissue and sitting on a basal lamina. An internal visceral layer surrounds the organs, while a parietal layer forms the walls of the body cavities. The serous membrane generally forms an airtight seal around the body cavity. The mesothelium cells produce glycosaminoglycans and other substances that act as a lubricant. The two mesothelium layers are able to move effortlessly over each other due to this thin layer of fluid between the two.

Serous membranes vary in size and complexity. The pericardium and the pleura are fairly simple, with smooth contours. The peritoneum is the largest membrane with a convoluted shape in some regions, and a surface area that can measure as much as the surface area of the skin (approximately 1.8 m2).

Serous Membrane Function

The serous membrane has a number of functions related to protection of the organs and body cavities which it encloses. It allows the frictionless movement of the heart and lungs, as well as the organs of the abdominal cavity. This allows movement of the smooth muscles without damage to the organs. As with any semi-permeable membrane, the serous membrane also acts to regulate movement of fluids and other substances across the membrane. Additional functions include the synthesis of cytokines and other molecules involved in membrane repair and inflammatory response, and the control of some immune responses including coagulation and movement of white blood cells.

Quiz

1. How many types of serous membrane are there?
A. 1
B. 2
C. 3
D. 4

Answer to Question #1
D is correct. There are four types of serous membranes: the pericardium that surrounds the heart, the pleura that surround the lungs, the peritoneum that surrounds the abdominal cavity and associated organs, and the tunica vaginalis that surrounds the testes.

2. Which is the largest serous membrane?
A. Pericardium
B. Pleura
C. Peritoneum
D. Tunica vaginalis

Answer to Question #2
C is correct. The peritoneum is the largest of the serous membranes. The peritoneum is very convoluted in some regions, folding in upon itself and increasing the surface area. The unfolded surface area of the peritoneum is close to that of the surface area of the skin.

3. What is an important function of the pericardium?
A. Transport oxygen to the lungs
B. Allow movement of the heart
C. Protect the kidneys
D. Remove toxins

Answer to Question #3
B is correct. The pericardium is the serous membrane that surrounds the heart. It has several protective functions including allowing movement of the heart within the body cavity without friction, protecting the heart from external stimuli by controlling inflammation and immune responses, and the synthesis and release of a number of molecules including cytokines and antigens.

References

  • Martin, E., & McFerran, T. A. (2014 online). Oxford, UK: Oxford University Press. eISBN: 9780191770395.
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