____ is directly related to the number of RBCs.

____ is directly related to the number of RBCs.

• A. Viscosity
• B. Temperature
• C. Density
• D. Elasticity

Answer: (A)

Viscosity is directly tied to how many red blood cells are in the blood. As the RBC count rises, the hematocrit (the fraction of blood made up of cells) increases, and the blood becomes thicker. More cells mean more internal friction and cell–cell interactions during flow, especially at low shear rates, which raises viscosity. Temperature can change viscosity but does not reflect RBC quantity, and density or elasticity are less directly related to the number of RBCs in the way viscosity is. So, the amount of RBCs most directly affects how thick the blood is, i.e., its viscosity.

Viscosity is directly tied to how many red blood cells are in the blood. As the RBC count rises, the hematocrit (the fraction of blood made up of cells) increases, and the blood becomes thicker. More cells mean more internal friction and cell–cell interactions during flow, especially at low shear rates, which raises viscosity. Temperature can change viscosity but does not reflect RBC quantity, and density or elasticity are less directly related to the number of RBCs in the way viscosity is. So, the amount of RBCs most directly affects how thick the blood is, i.e., its viscosity.