What is a vesicle?

A vesicle is accurately defined as a small fluid-filled sac under the skin. This structure is often the result of various conditions, including inflammatory processes or infections, and can contain serum, lymph, or pus. Vesicles are commonly observed in the context of skin disorders such as blisters, which form when the outer layer of skin is damaged and fluids accumulate.

Other options describe different biological structures: muscle types pertain to the composition and function of muscular tissue, blood cells refer to the various types of cells in the bloodstream like red blood cells or white blood cells, and a large vessel in the chest could refer to anatomical structures such as the aorta or pulmonary arteries, which are involved in transporting blood. Each of these descriptions distinguishes them from vesicles, further reinforcing the specificity of vesicles as small, fluid-filled sacs.