A liquid substance that continually circulates through the body, which is made up of plasma, red blood cells (erythrocytes), white blood cells (leukocytes), and platelets; blood The most important function of blood is to transport oxygen to the body via haemoglobin (in the red blood cells). Blood also circulates away waste matter and carbon dioxide, and brings nourishment, electrolytes, hormones, vitamins, antibodies, and heat. Cats have 3 blood Blood Type.