What is the term for the narrowing of an opening in a biological structure?

The term "stenosis" specifically refers to the narrowing of an opening or passage in a biological structure, such as blood vessels or heart valves. This condition often leads to decreased blood flow or pressure changes and can have significant physiological consequences. Stenosis is a common term used in various medical contexts, including cardiovascular health, where it might describe a narrowed artery that restricts blood flow or a heart valve that does not open fully.

Atresia is a condition where an opening that should exist is completely absent, as seen in certain congenital defects. Stricture also describes the narrowing of a tubular structure but is often used in a more localized context, such as in digestive or urinary tracts. Dilation, on the other hand, is the opposite of stenosis; it refers to the widening or expansion of a structure.

Thus, the choice of stenosis as the correct answer is appropriate because it accurately defines the specific condition of narrowing in biological structures.