Arteries, autonomic regulation

Blood is supplied to the retina by the central retinal artery and choroidal blood vessels (Oyster, 1999). The central retinal artery arises from the ophthalmic artery, w hich in turn branches off the internal carotid artery. Upon entering the retina, the central retinal artery branches into deep capillary beds in the INL and superficial capillary beds in the GCL. Endothelial cells of retinal capillaries are joined by tight junctions, contributing to the blood/retinal barrier. There is litde or no autonomic regulation of the retinal circulation blood flow through these capillaries is instead primarily controlled by autoregulation (Wangsa-Wirawan and Linsenmeier, 2003). Retinal capillaries drain into the central retinal vein. 

Equally as important, and potentially more clinically relevant, are the indirect mechanisms responsible for the antiarrhythmic activity of calcium inhibitory agents, including coronary vasodilation and subsequent increases in coronary artery blood flow (47, 114, 124, 157) decreased cardiac contractility, metabolism, and arterial vasodilation resulting in decreases in myocardial oxygen consumption and wall tension (92) and reflex alterations in autonomic regulation of heart rateToverdrive supression) and AV conduction (114) ... 

Autonomic nerves can regulate coronary arteriolar tone. Acetylcholine released from postganglionic parasympathetic nerves relaxes coronary arteriolar smooth muscle via the NO/cGMP pathway in humans as described above. Damage to the endothelium, as occurs with atherosclerosis, eliminates this action, and acetylcholine is able to contract arterial smooth muscle and produce vasoconstriction. Skeletal muscle receives sympathetic cholinergic vasodilator nerves, but the view that acetylcholine caused vasodilation in this vascular bed has not been verified experimentally. Moreover, NO, rather than acetylcholine, may be released from neurons. However, this vascular bed responds to exogenous choline esters because of the presence of M3 receptors on endothelial and smooth muscle cells. 

The central and autonomic nervous systems are intricately involved in the regulation of arterial BP. A number of receptors that either enhance or inhibit norepinephrine release are located on the presynaptic surface of sympathetic terminals. The a and /S presynaptic receptors play a role in negative and positive feedback to the norepinephrine-containing vesicles located near the neuronal ending. Stimulation... 

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