Sickle cells

Erytrocytes deformation to sickle shapes.

A sickle cell crisis can be set off by temperature changes, stress, dehydration, and high altitude, causing, among other things, hemoltic anemia.
The sickling of the erytrocytes is caused by deoxygenation of the red blood cells and decrease the cell’s elasticity and they will fail to return to normal shape when normal oxygen tension is restored.
As they pass through the narrow capillaries leading to obstruction of capillaries and restrict blood flow to organs, resulting in ischaemia, pain, necrosis, and often organ damage.