What separates Interstitial Fluid (ISF) from Plasma in the Extracellular Fluid?

• A. White blood cells
• B. Epithelial cells
• C. Adipose tissue
• D. Cilia

Answer: (B)

The component that separates interstitial fluid (ISF) from plasma in the extracellular fluid is epithelial cells. Epithelial cells form barriers that regulate the movement of substances between different compartments in the body. In the case of ISF and plasma, the epithelial cells are specifically part of the capillary walls, which separate the plasma within the blood vessels from the interstitial fluid surrounding the cells in tissues.

This separation is crucial for maintaining different solute concentrations and facilitating the exchange of nutrients, gases, and waste products between the blood and the tissues. The endothelial cells of capillaries are selectively permeable, allowing certain substances to pass while restricting others, thus ensuring proper physiological function and homeostasis.

The other options are not directly involved in creating a barrier between ISF and plasma. White blood cells are involved in immune responses, adipose tissue is specialized for fat storage, and cilia are involved in movement or signaling, but none of these elements serve to separate interstitial fluid from plasma like epithelial cells do.