Blood is a special connective tissue consisting of a fluid matrix called plasma and formed elements. The formed elements include Erythrocytes (RBCs), Leucocytes (WBCs), and Platelets. Therefore, Blood = Plasma + RBC + WBC + Platelets , . Serum is defined as plasma without clotting factors (like fibrinogen) . Lymph is similar to blood but lacks RBCs and some proteins .