White blood and red blood cells

White blood cells (leukocytes) are part of the immune system. They help the body fight infection and disease. There are several types of white blood cells, each with a specific role in defending the body.

Red blood cells (erythrocytes) are the most common type of blood cell. Their main function is to transport oxygen from the lungs to the body's tissues and to carry carbon dioxide back to the lungs. They contain hemoglobin, a protein that binds to oxygen.