Which of the following components is NOT found in tissue fluid?

Tissue fluid, also known as interstitial fluid, is the fluid that surrounds the cells in tissue spaces. Its primary function is to provide a medium for nutrient, waste, and gas exchange between blood and cells.

The correct answer, stating that red blood cells are not found in tissue fluid, is accurate because red blood cells typically remain confined within blood vessels. Their main function is to transport oxygen from the lungs to the body's tissues and return carbon dioxide to the lungs, and they do not leak out of capillaries into the surrounding tissue fluid under normal physiological conditions.

In contrast, plasma proteins, while primarily found in blood plasma, can also be present in smaller amounts in tissue fluid, influencing osmotic pressure and fluid balance. Electrolytes, such as sodium and potassium, are freely exchanged between the blood and tissue fluid to help maintain ion balance and pH levels, so they are commonly found in tissue fluid. White blood cells are part of the immune response and can migrate into tissue fluid during various physiological or inflammatory processes, making their presence in tissue fluid common in certain conditions.