a. A bursa (figure 3-3) is the simplest of serous cavities. Each bursa is a small sac located between two moving structures, usually a muscle moving over a bony surface. The bursa reduces the friction between the two structures. For example, a bursa prevents excessive friction between the skin and patella (knee cap). This bursa, called the prepatellar bursa, allows the skin to move freely over the patella. (When injured, it produces excessive amounts of the serous fluid and is known as "housemaid's knee.")
1. SEROUS (BURSAL) CAVITY:
a. SPACE CONTAINING JUST ENOUGH SEROUS FLUID TO MOISTEN INNER SURFACE.
b. SPACE ARTIFICIALLY WIDENED FOR DIAGRAMMATIC PURPOSES.
2. (BURSAL) CAPSULE:
a. BAG-LIKE — SURROUNDING THE SEROUS CAVITY.
b. FCT MEMBRANE MAIN STRUCTURAL ELEMENT.
c. A SEROUS MEMBRANE (SIMPLE SQUAMOUS EPITHELIAL TISSUE) AS AN INNER LINING OF THE CAPSULE. THE SEROUS MEMBRANE INCLOSES THE SEROUS CAVITY AND SECRETES THE SEROUS FLUID.
b. As a fibrous sac, each bursa has a central cavity which is lined with a serous membrane. This membrane is a simple squamous epithelium. The serous membrane secretes a serous fluid into the serous cavity. The serous fluid is the lubricant, minimizing friction.
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