# Serous Membranes --- **Serous membranes**, or simply the **serosa** are part of the an [[tissue]] that lines the [[body cavity#Ventral Cavity|ventral body cavities]] that are not open to the outside. They surround and protect the [[organ|organs]] that live there. As epithelial membranes, they are made from [[epithelial tissue]] on the apical surface and [[connective tissue]] on the basal surface. The epithelial portion of the membrane is referred to as the **mesothelium**. **Serous fluid** is a lubricating fluid with about the consistency of oil that is secreted by the epithelium into the **serous cavity**. It allows the organs to move around against each other without causing too much friction. ## Structure: Parietal & Visceral Serosa Serous membranes almost look like a two layered membrane, but they are actually their own balloon-like structures that are doubled-up and folded in on themselves, with the organs they are protecting living in the inside pocket. The part of the membrane that is towards the outside of the "balloon" is the **parietal** side, and the inside side is the **visceral** side. The area between the parietal and visceral membranes—the "inside" of the balloon—is the **serous cavity** and is filled with a thin layer of **serous fluid** produced by the membrane itself. ![[serous membrane.png]] ## Differentiation Serous membranes are named for their locations within the body—or more specifically for what organs they surround and protect. - The [[pericardium]] surrounds and protects the heart. - Two [[pleura]] line the thoracic cavity and surround and protect each lung. - The [[peritoneum]] lives in the abdominopelvic cavity. ___