This document provides an overview of hematology, including the composition and functions of blood. It discusses the main components of blood - plasma, red blood cells, white blood cells, and platelets. Red blood cells carry oxygen and carbon dioxide throughout the body. White blood cells help fight infection. Platelets help the blood clotting process. The document also covers serum and plasma, anticoagulants, where blood cells originate from, and the normal collection of blood.