Which structure is primarily responsible for filling during an erection when using PDE5 inhibitors?

The corpora cavernosa play a central role in the physiological process of achieving an erection, especially when facilitated by PDE5 inhibitors. During sexual arousal, nitric oxide is released, leading to the generation of cyclic guanosine monophosphate (cGMP), which helps relax the smooth muscle in the corpora cavernosa. This relaxation allows blood to flow into these cavernous tissues, leading to engorgement and resulting in an erection.

PDE5 inhibitors work by blocking the phosphodiesterase type 5 enzyme, which degrades cGMP. By preventing the breakdown of cGMP, these inhibitors enhance and prolong its effects, further promoting blood flow into the corpora cavernosa during sexual stimulation. Thus, the primary structure responsible for the filling of the penis during an erection, particularly when using these medications, is indeed the corpora cavernosa.