Does parasympathetic innervation cause vasodilation or vasoconstriction of uveal blood vessels?

Parasympathetic innervation primarily causes vasodilation of uveal blood vessels. This effect is mediated by the release of neurotransmitters such as acetylcholine, which acts on muscarinic receptors in the vascular smooth muscle. When these receptors are activated, they lead to relaxation of the smooth muscle fibers, resulting in an increase in the diameter of the blood vessels. This vasodilation allows for increased blood flow to the uveal tissues, which is particularly important for maintaining metabolic functions and nutrient delivery in the eye.

In the context of uveal physiology, the increase in blood flow can have important implications for intraocular pressure and overall ocular health. The parasympathetic system is also involved in processes such as accommodation and miosis, which further underscores its role in regulating the ocular environment.

The other options reflect different physiological mechanisms or effects that do not accurately represent the response of uveal blood vessels to parasympathetic stimulation. Thus, the correct association with parasympathetic innervation is indeed vasodilation.