What is serous fluid?

• A. Lubricating fluid that separates serous membranes.
• B. A digestive enzyme produced by membranes.
• C. A hormone secreted by serous membranes.
• D. Blood plasma within serous membranes.

Answer: (A)

Serous fluid is the lubricating, watery fluid that fills the small space between the two layers of serous membranes, allowing them to slide past each other with minimal friction as organs move. It’s produced by the serous membranes themselves and is a clear ultrafiltrate of blood plasma, not an enzyme, hormone, or the blood plasma itself being housed inside the membranes. This lubrication is essential for easy movement of the lungs, heart, and abdominal organs during breathing, heartbeat, and digestion.