Vascular permeability

Illustration of the Enhanced Permeability and Retention (EPR) effect.

Vascular permeability refers to the capacity of blood vessel walls to allow the flow of small molecules (such as ions, nutrients, and water) or even whole cells (such as lymphocytes) in and out of the vessel. This process is crucial for maintaining tissue homeostasis and is involved in various physiological and pathological processes.

Mechanism

Vascular permeability is primarily regulated by the endothelial cells that line the interior surface of blood vessels. These cells form a barrier that controls the passage of substances. The permeability of this barrier can be modulated by various factors, including inflammatory cytokines, growth factors, and shear stress.

The tight junctions and adherens junctions between endothelial cells play a significant role in maintaining the integrity of the vascular barrier. Disruption of these junctions can lead to increased permeability.

Physiological Role

In normal physiology, vascular permeability is essential for the delivery of nutrients and oxygen to tissues and the removal of waste products. It also plays a role in the immune response by allowing immune cells to exit the bloodstream and enter tissues where they are needed.

Pathological Conditions

Increased vascular permeability is a hallmark of several pathological conditions, including inflammation, tumor growth, and edema. In inflammation, for example, increased permeability allows immune cells to access the site of infection or injury. However, excessive permeability can lead to tissue damage and contribute to disease progression.

Enhanced Permeability and Retention (EPR) Effect

The Enhanced Permeability and Retention (EPR) effect is a phenomenon observed in tumor biology where the leaky vasculature of tumors allows for the accumulation of macromolecules and nanoparticles. This effect is exploited in the design of nanomedicines for targeted drug delivery to tumors.

Related Pages

• Endothelial cell
• Inflammation
• Tumor biology
• Nanomedicine

References

• Jain, R. K. (1987). Transport of molecules in the tumor interstitium: a review. *Cancer Research*, 47(12), 3039-3051.
• Maeda, H., Wu, J., Sawa, T., Matsumura, Y., & Hori, K. (2000). Tumor vascular permeability and the EPR effect in macromolecular therapeutics: a review. *Journal of Controlled Release*, 65(1-2), 271-284.