Arthritis is more common among adults 65 and older, but it can affect people of all ages, including children. The main function of human red blood cells or erythrocytes is usually to carry oxygen to several areas of the body. Their natural beautiful red colors comes from a biomolecule called hemoglobin which binds oxygen and occupies the cytoplasm of the cell. Unlike most human cells, red blood cells don't have nuclei or other organelles (the components or subunits of many cells). Their biconcave appearance can clearly be seen with this image which was captured using a scanning electron microscope (SEM). Looking like doughnuts without holes, they're flat and depressed inside center and also have a dumbbell-shaped cross-section. This unusual form is very important for his or her function because it is great for their smooth passage through minor and major veins.