concealed accessory pathway
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a course usually followed. In neurology, the nerve structures through which a sensory impression is conducted to the cerebral cortex (afferent pathway), or through which an impulse passes from the brain to the skeletal musculature (efferent pathway). Also used alone to indicate a sequence of reactions that convert one biological material to another (metabolic pathway).
accessory pathway (accessory conduction pathway) extra muscle tissue between the atrium and ventricle that bypasses all or part of the normal conduction system. When the ventricles are activated prematurely via this pathway, initial forces are slow, producing the delta wave of wolff-parkinson-white syndrome, and preexcitation is said to exist; the delta wave causes the PR interval to shorten and the QRS interval to broaden.
alternative complement pathway see complement.
amphibolic pathway a group of metabolic reactions with a dual function, providing small metabolites for further catabolism to end products or for use as precursors in synthetic, anabolic reactions. The tricarboxylic acid cycle is an example. See also anabolism and catabolism.
biosynthetic pathway the sequence of enzymatic steps in the synthesis of a specific end-product in a living organism.
classical complement pathway see complement.
coagulation p's see common p. of coagulation, extrinsic p. of coagulation, and intrinsic p. of coagulation.
common pathway of coagulation the steps in the mechanism of coagulation (see clotting) from the activation of factor x through the conversion of fibrinogen to fibrin. See also intrinsic pathway of coagulation and extrinsic pathway of coagulation.
concealed accessory pathway an accessory pathway that has only retrograde conduction; thus its PR and QRS complexes are normal on the electrocardiogram, but there is a tendency to develop premature supraventricular tachycardia. If atrial fibrillation develops, conduction will proceed across the atrioventricular node.
Embden-Meyerhof pathway the series of enzymatic reactions in the anaerobic conversion of glucose to lactic acid, resulting in energy in the form of adenosine triphosphate (ATP).
extrinsic pathway of coagulation the mechanism that produces fibrin following tissue injury, beginning with formation of an activated complex between tissue factor and factor vii and leading to activation of factor x, which induces the reactions of the common pathway of coagulation. See also intrinsic pathway of coagulation.
final common pathway
1. the motor neurons by which nerve impulses from many central sources pass to a muscle or gland in the periphery.
2. any mechanism by which several independent effects exert a common influence.
intrinsic pathway of coagulation a sequence of reactions leading to fibrin formation, beginning with the contact activation of factor xii. This is followed by the sequential activation of factors xi and ix, which results in the activation of factor x. Activated factor X (factor Xa) initiates the common pathway of coagulation. See also extrinsic pathway of coagulation.
pentose phosphate pathway a pathway of hexose oxidation in which glucose-6-phosphate undergoes two successive oxidations by NADP, the final forming a pentose phosphate.