Conductivity tissue

The most frequently used classification system is that proposed by Vaughan Williams (Table 6-1). Type la drugs slow conduction velocity, prolong refractoriness, and decrease the automatic properties of sodium-dependent (normal and diseased) conduction tissue. Type la drugs are broad-spectrum antiarrhythmics, being effective for both supraventricular and ventricular arrhythmias. 

Schlerenchyma Thick cell walls containing lignin-nonextensible secondary walls, lack protoplasts at maturity, living or dead at functional maturity Strength and supporting elements of plant parts, scattered throughout plant (also see conducting tissue)... 

Sclerenchyma Conductive tissue Sclerenchyma cells Mechanical support... 

Damage is usually caused by a blockage of the water-conducting tissues of the stem, starving the leaves of water. Wilts can persist in the soil for several years, entering plants through wounds. Commonly associated with eelworm attack. Some wilts, e.g., of China asters and peas, are host-specific, while others attack a wide range of plants. 

The place of the dmg in dentistry [153 4] and in electro-convulsive therapy [ 154] (with a description of a technique to surmount difficulties arising from the concurrent use ot suxamethonium) has been evaluated. A refined radio telemetric technique has enabled a detailed study [155] of the cardiovascular effects of propanidid to be made, resulting in strong evidence for a transient procainamide- or quinidine-like depression of myocardial conductive tissue. The above publications [150-5] quote a large number of relevant references. 

Lignin is found in plant cell walls of supporting and conducting tissue, mostly the trac-heids and vessel parts of the xylem. It is largely found in the thickened secondary wall but can occur elsewhere close to the celluloses and hemicelluloses. 

The heart is innervated by both sympathetic and parasympathetic neurons however, their distribution in the heart is quite different. Postganglionic noradrenergic fibers from the stellate and inferior cervical ganglia innervate the sinoatrial (S-A) node and myocardial tissues of the atria and ventricles. Activation of the sympathetic outflow to the heart results in an increase in rate (positive chronotropic effect), in force of contraction (positive inotropic effect), conduction tissue (positive dro-motropic effect). 

The effects of disopyramide on the myocardium and specialized conduction tissue (Table 16.2) are a composite of its direct actions on cardiac tissue and its indirect actions mediated by competitive blockade of muscarinic cholinergic receptors. 

Lidocaine does not usually change the PR, QRS, or QT interval, although the QT may be shortened in some patients. The paucity of electrocardiographic changes reflects lidocaine s lack of effect on healthy myocardium and conducting tissue. 

Digitalis is the drug of choice in atrial fibrillation for controlling ventricular rate. Its effect is due to the prolongation of the refractory period of the conducting tissue. The dose in so adjusted as to maintain the ventricular rate of 60 to 80 beats per minute at rest and approximately 100 beats per minute during light exercise. 

In general, in various parts of the conduction system higher amounts of connexin were found especially in the fast conducting tissues as compared to ventricular myocardium. Only minimal expression of Cx37 and Cx46 between occasional atrial and ventricular myocytes has been observed [Davis et al.,... 

For instance, cardiac expression of TASK and TREK (both in the myocardium and conductive tissue) is compatible with bradycardia and the negative inotropic effect observed with volatile anesthetics (Terrenoire et al., 2001). 

WOOD. A vascular tissue which occurs in all higher plants The most important commercial sources of wood are the gymnosperms, or softwood trees and the dicotyledonous angiosperms, or hardwood trees. Botanically, wood serves the plant as supporting and conducting tissue, and it also contains certain cells which serve in the storage of food. The trunks and branches of trees and shrubs are composed of wood, except for the very narrow cylinder of pith in the center and the bark which covers the outside. Botanists refer to wood by its Greek name, xylem. 

Special interest adheres to the group of cholinesterases (ChE), not only in view of their physiological role in conductive tissues, but also because their specific behavior towards substrates and inhibitors and their high efficiency towards cationic substrates permit exact kinetic measurements. In spite of an enormous amount of experimental work, the exact structure of the active surface of cholinesterases is still controversial [see the review of Whittaker (/)]. The following representation will discuss the results already achieved and point out the many problems in this field still awaiting solution. 

It was recognized at the start of the 20th century that reentry in simple in vitro models (eg, rings of conducting tissues) was permanently interrupted by transecting the reentry circuit. This concept has now been applied to treat clinical arrhythmias that occur as a result of reentry in anatomically delineated pathways. For example, interruption of accessory atrio-ventricular connections can permanently cure arrhythmias in patients with the Wolff-Parkinson-White syndrome. Such... 

Talreja DR, Nishimura RA, Edwards WD, et al. Alcohol septal ablation versus surgical septal myectomy comparison of effects on atrioventricular conduction tissue, J Am Coll Cardiol 2004 44 2329-2332. 

Hardwoods contain several cell types, specialized for different functions (Fig. 1-9). The supporting tissue consists mainly of libriform cells, the conducting tissue of vessels with large cavities, and the storage tissue of ray parenchyma cells. In addition, hardwood contains hybrids of the above-mentioned cells which are classified as fiber tracheids. Although the term fiber is frequently used for any kind of wood cells, it more specifically denotes the supporting tissue, including both libriform cells and fiber tracheids. In birch these cells constitute 65 to 70% of the stem volume. 

Eye mydriasis Heart (p,[S/ increased race (SA node) increased automaticity (AV rode and muscle) increased velocity in conducting tissue increased contractility of myocardium increased Oj consumption decreased refractory period of all tissues... 

Calciiun is involved in the initiation of smooth muscle and cardiac cell contraction and in the propagation of the cardiac impulse. Actions on cardiac pacemaker cells and conducting tissue are described in Chapter 24. 

The differences between their clinical effects can be explained in part by their binding to different parts of the L-type calcium channel. All members of the group are vasodilators, and some have negative cardiac inotropic action and negative chronotropic effect via pacemaker cells and depress conducting tissue. The attributes of individual drugs are described below. 

Altered rate of automatic discharge or abnormality of the mechanism by which an impulse is generated from a centre in the nodes or conducting tissue, is one cause of cardiac arrhythmia, e.g. atrial fibrillation, flutter or tachycardia. 

On SA and AV nodes and conducting tissue decreased generation and propagation. 

All antidysrhythmic drugs have effects on the cardiac conducting tissues and can all therefore cause cardiac dysrhythmias. 

Care must be taken in patients with pre-existing conduction tissue disease or heart failure. Loading doses should be reduced in cardiac failure, because of a lowered apparent volume of distribution (67). 

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