What physiological response occurs in non-elastic tissues due to heat?

The correct choice highlights the effect of heat on non-elastic tissues, particularly regarding collagenous structures, which comprise a significant part of connective tissues. When heat is applied to non-elastic tissues, it promotes an increase in the extensibility of collagen fibers. This occurs because elevated temperatures lead to changes in the collagen structure, allowing for greater elongation and flexibility.

As the temperature rises, the viscoelastic properties of the collagen change, enabling these tissues to stretch more easily. This property is particularly beneficial in therapeutic contexts, as it can enhance mobility and reduce stiffness in joints and muscles, facilitating rehabilitation and recovery from injuries.

In contrast, while reduction in pain perception may occur with heat, it is not a direct physiological response specific to non-elastic tissues. Decreased blood flow is typically associated with cooling rather than heating. Additionally, constriction of blood vessels happens with mechanisms such as cold therapy or in certain pathological states, but heating generally promotes vasodilation, which increases blood flow to the tissues. Thus, the notion of increased extensibility of collagen, specifically in response to heat, is the most pertinent physiological response in this context.