Aplastic crisis is caused by a decrease in the production of red blood cells in the bone marrow.

Sequestration crisis involves the blockage of small blood vessels by sickled red blood cells.

Vaso-occlusive crisis is characterized by the pooling of large amounts of blood in the spleen and liver.

Aplastic crisis is characterized by the pooling of large amounts of blood in the spleen and liver.

Sequestration crisis is characterized by the pooling of large amounts of blood in the spleen and liver.

Vaso-occlusive crisis involves the blockage of small blood vessels by sickled red blood cells.