False-colour scanning electron micrograph (SEM) of the abnormal type of red blood cell that causes sickle-cell anaemia. This inherited disease is named for the characteristic, long, curving deformity of the red cell, or erythrocyte. The other cell in this micrograph is an echinocyte, another example of the varied shapes red cells can adopt. Red cells develop the sickle shape when the synthesis of haemoglobin is defective; the haemoglobin molecules form into tiny rods, which assemble into sheaves & stretch the cell membrane. Unlike normal red cells, sickle cells are rigid; they block fine capillaries, obstructing blood supply & depriving tissue of oxygen & nutrients. Ref: Microcosmos, fig. 2.44, page 38.