A common trait of serous fluids is their role in assisting digestion, excretion, and respiration.
Minor salivary glands of von Ebner present on the tongue secrete the lipase.
The other major salivary glands produce mixed (serous and mucus) saliva.
Serous membrane fluid collects on microvilli on the outer layer and acts as a lubricant and reduces friction from muscle movement.
Serum includes all proteins not used in coagulation (clotting) and all the electrolytes, antibodies, antigens, hormones and any exogenous substances, such as drugs and microorganisms.