Briefly describe the components of blood and their functions.

55% of blood is made up of plasma. This liquid component holds the other component of blood, cells, in suspension and thus is vitally important to their transport. Plasma is also important in transporting not just cells, but also a range of other things such as heat, hormones, energy substrates (such as glucose), and waste products (such as urea). The other 45% of blood is made up of a range of cell types. There are 3 key cell types: red blood cells (RBCs), white blood cells (WBCs), and platelets. RBCs are important in oxygen transport, with their haemoglobin being key to this. WBCs are immune cells, defending the body from infection. Platelets main function is to form blood clots; this prevents too much blood loss if an injury is sustained.