How does the abnormal shape of a sickled red blood cell affect its movement through blood vessels?

• A. It becomes more flexible and moves freely through vessels.
• B. It cannot move easily through the blood vessels
• C. It dissolves in the blood plasma
• D. It moves quickly through the blood vessels

Answer: (B)

Movement of red blood cells through vessels relies on their ability to deform. Normal RBCs are flexible and biconcave, so they can squeeze through tiny capillaries even when the vessel is narrower than the cell. In sickle cell disease, hemoglobin S polymerizes when oxygen levels fall, turning the cells into a rigid, crescent shape. This loss of deformability makes them unable to bend and pass smoothly through small vessels, so they move slowly or get stuck, reducing blood flow and oxygen delivery to tissues. That blocking tendency explains why the correct choice notes that these cells cannot move easily through the blood vessels. The other options don’t fit because the sickled cells do not become more flexible, dissolve in plasma, or move quickly.