Viscosity

Definition

Viscosity is a measure of the internal friction or resistance to flow within a fluid. It describes a fluid's thickness or resistance to pouring and is an important factor in the study of blood and its flow through the circulatory system.

5 Must Know Facts For Your Next Test

1. Viscosity is a key determinant of blood flow through the circulatory system, with higher viscosity leading to increased resistance to flow.
2. The viscosity of blood is primarily influenced by the concentration of red blood cells, as they are the largest cellular component.
3. Increased hematocrit, or the percentage of red blood cells, leads to higher blood viscosity, which can contribute to cardiovascular conditions.
4. Shear stress, the force applied to a fluid, interacts with viscosity to determine the rate of blood flow through the vessels.
5. Unlike Newtonian fluids, the viscosity of blood changes depending on the shear stress applied, making it a non-Newtonian fluid.

Review Questions

• Explain how viscosity affects blood flow through the circulatory system.
  • Viscosity is a crucial factor in determining the flow of blood through the circulatory system. Higher blood viscosity, which is influenced by the concentration of red blood cells (hematocrit), leads to increased resistance to blood flow. This resistance can impede the delivery of oxygen and nutrients to tissues and increase the workload on the heart to maintain adequate circulation. Conversely, lower blood viscosity facilitates more efficient blood flow, reducing the strain on the cardiovascular system.
• Describe the relationship between shear stress and viscosity in the context of blood flow.
  • The interaction between shear stress and viscosity is a key determinant of blood flow through the vessels. Shear stress is the force applied to a fluid, such as blood, that causes it to flow. Viscosity, on the other hand, is a measure of the internal friction or resistance to flow within the fluid. These two factors work together to influence the rate of blood flow. Specifically, higher shear stress applied to a fluid with higher viscosity, such as blood, will result in a lower flow rate compared to a fluid with lower viscosity. This non-Newtonian behavior of blood, where its viscosity changes based on the applied shear stress, is an important consideration in understanding blood flow dynamics within the circulatory system.
• Analyze how changes in hematocrit can impact blood viscosity and cardiovascular health.
  • The hematocrit, or the percentage of red blood cells in the total volume of blood, is a significant factor in determining blood viscosity. An increase in hematocrit, which can occur in conditions like polycythemia or dehydration, leads to higher blood viscosity. This increased viscosity results in greater resistance to blood flow through the circulatory system, forcing the heart to work harder to maintain adequate perfusion of tissues. Elevated blood viscosity can contribute to the development of cardiovascular diseases, such as hypertension, atherosclerosis, and thrombosis, by increasing the workload on the heart and impairing the delivery of oxygen and nutrients to vital organs. Monitoring and managing hematocrit levels is, therefore, an important consideration in maintaining cardiovascular health.

Related terms

Hematocrit: The percentage of red blood cells in the total volume of blood, which affects the viscosity of blood.

Shear Stress: The force applied to a fluid that causes it to flow, which interacts with viscosity to determine the rate of blood flow.

Newtonian Fluid: A fluid whose viscosity remains constant regardless of the applied shear stress, unlike non-Newtonian fluids like blood.