Dilation of vessels

Under internal pressure a vessel will expand slightly. The radial growth can be calculated from the elastic strain in the radial direction. The principal strains in a two-dimensional system are related to the principal stresses by  

The radial (diametrical strain) will be the same as the circumferential strain e2. For any shell of revolution the dilation can be found by substituting the appropriate expressions for the circumferential and meridional stresses in equation 13.36. 

So for a cylinder closed by a hemispherical head of the same thickness the difference in dilation of the two sections, if they were free to expand separately, would be  

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NO (molecular weight = 30) is small but plays a big role in physiological regulation, not least in the vasculature where its effects were first seen (see Chapter 4). Endothelium-derived relaxation factor (EDRF) was discovered its ability to cause dilatation of vessels by relaxing the arterial muscle layer. Only much later was EDRF discovered to be a gas, nitric oxide. More recent interest in NO is based on the evidence that it is antiatherogenic. The pathogenesis of atherosclerosis is complex but many of the known effects of NO can be implicated in this common and serious condition. 

Therefore, it is very likely that contraction of nonvascular smooth muscle is an effect of activation of Hj receptors, while secretion of digestive juice and increased heart rate are connected to activation of H2 receptors and dilation of vessels and increased permeability of capillaries is a result of combined activation of both types of receptors. 

It seems likely that the mechanism of action of all of the organic nitrates and nitrites should be analogous. They exhibit direct relaxant effects on vascular, smooth musculature, which results in general dilation of vessels—predominantly veins, bnt also arteries to a... 

Eye miosis and spasm of the ciliary muscle occur so that the eye is accommodated for near vision. Intraocular pressure falls due, perhaps, to dilation of vessels at the point where intraocular fluids pass into the blood. 

Dilation of vessels in muscle, constriction of cutaneous vessels, and positive inotropic and chronotropic effects on the heart are all actions of (A) Acetylcholine... 

Mucous membranes with slight flush, slight dilation of perilimbal vessels +1 = Definite congestion above normal, mucous membranes with definite flush, marked dilation of vessels... 

Slight oilation of pericorneal vessels +1 = Definite dilation of vessels... 

Marked dilation of vessels running toward palpebral conjunctiva or marked congestion... 

Dilating tendency of vessels and swelling tendency of membranes +1 = Definite dilation of vessels, perilimbal congestion +2 = Marked dilation of vessels, congestion of membranes... 

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