Which structure is described as a blister-like formation that contains serous fluid?

The structure described as a blister-like formation containing serous fluid is indeed a vesicle. Vesicles are small, fluid-filled cavities that can form on the skin or within the body and are typically less than 1 cm in diameter. They are characterized by their thin walls and the clear fluid they contain, distinguishing them from other fluid-filled lesions.

Pustules, while also fluid-filled, specifically contain pus rather than serous fluid, which is typically a clear, watery substance. An abscess is a larger accumulation of pus due to infection, encased in a wall created by the body’s immune response. An ulcer, on the other hand, refers to a loss of skin or mucous membrane and is not a fluid-filled structure.

Thus, the defining characteristic of a vesicle as a small, blister-like formation that contains serous fluid aligns perfectly with the description given in the question.