Diseased vessels are ____________ and are not capable of dilation.

Diseased vessels are calcified and are not capable of dilation due to the accumulation of calcium deposits within the vascular walls. This calcification leads to stiffening of the blood vessels, which impairs their ability to respond to physiological demands by dilating. Normally, healthy blood vessels can adapt by widening (dilating) to increase blood flow or narrow (constrict) to reduce blood flow based on the body’s requirements. However, when calcification occurs, this flexibility is lost, leading to reduced compliance and impaired function of the vessels.

The other terms related to vascular condition, like thickened, congested, or degenerated, describe various aspects of disease processes in blood vessels but do not specifically highlight the major impact on dilation capacity as calcification does. Thickened vessels may indicate an increase in muscle layer thickness but still retain some ability for dilation. Congested vessels refer to an excess of blood or fluid, while degenerated vessels imply deterioration, but neither indicates the precise mechanism of stiffness and loss of dilation capability as calcification does.