A sickle cell is an oddly shaped red blood cell that contains hemoglobin S instead of hemoglobin A. This causes the crescent shape of the cell. It often blocks capillary openings and can't hold a sufficient amount of oxygen for the body's cells.

The Shape of a Sickle Cell

This is how a sickle cell might look in the bloodstream.

    Red blood cells have 280 million hemoglobin molecules which attract oxygen. The importance of hemoglobin is extreme. The dysfunctional hemoglobin S causes loss of oxygen for the red blood cell.  Lack of oxygen in the red blood cell creates tough rods called polymers, which changes the shape of the cell. A sickle cell's lifespan is only 10-20 days compared to the red blood cell's normal life of 90-120 days.

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Formation

    The tough rods called polymers and crystals harden red blood cells. Then the cell is called a sickle cell. It's special hemoglobin S which is inherited from parents causes it to become a certain crescent shape. Click the link below to watch the video below for an animated explanation of sickle cell formation.
http://www.youtube.com/watch?v=9UpwV1tdxcs