Red Blood Cells, Their Functions, and their Types.
Red blood cell also called erythrocyte, cellular component of blood, millions of which in the circulation of vertebrates give the blood its characteristics colour and carry oxygen from the lungs to the tissues. The mature humans red blood cell is small, round, and biconcave; it appears dumbbell-shaped in profile. The cell is flexible and assumes a bell shape as it passes through extremely small blood vessels. It is covered with a membrane composed of lipids and proteins, lacks a nucleus and contains haemoglobin—a red iron-rich protein that binds oxygen.