Serous fluid major salivary glands produce mixed (serous and mucus) saliva. Another type of serous fluid is secreted by the serous membranes (serosa), two-layered membranes which line the body cavities. Serous membrane fluid collects on microvilli on the outer layer and acts as a lubricant and reduces friction from muscle movement. This can be seen in the lungs, with the pleural cavity. Blood serum is the component of blood that is neither a blood cell, nor a clotting factor. Blood serum and blood plasma are similar, but serum does not contain any clotting factors, such as fibrinogen, prothrombin, thromboplastin and many others.
Blood donation in England and each donation usually gives two or three adult doses. One adult dose of platelets would otherwise require four whole blood donations. Blood is made in the bone marrow. It is composed of red blood cells, platelets, plasma and white blood cells, collectively referred to as blood components. Donations given at regular blood donation sessions are referred to as "Whole Blood". Platelets are very small cells. They work with the clotting factors in plasma to form a mesh "plug" to stop or prevent bleeding. Plasma is the fluid part of the blood. It contains protein, salts and clotting factors. White