Serous fluids are best described as...

• A. Derived from serum and provide lubrication and protection
• B. Derived from serum and do not provide lubrication
• C. Derived from urine
• D. Derived from lymph and provide protection

Answer: (A)

Serous fluids are the thin, watery secretions produced by the serous membranes that line body cavities. They originate mainly as a filtrate of plasma (the serum portion of blood) and form a lubricating layer in the serous spaces. This lubrication reduces friction between moving surfaces such as the lungs, heart, and abdominal organs, and it also provides basic protection. Because of their origin from serum and their role in lubrication and protection, the description that they are derived from serum and provide lubrication and protection best fits. They are not derived from urine, nor from lymph.