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 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.
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
biosynthetic pathway the sequence of enzymatic steps in the synthesis of a specific end-product in a living organism.
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).
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.
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.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
pen·tose phos·phate path·way
a secondary pathway for the oxidation of d-glucose (not occurring in skeletal muscle), generating reducing power (NADPH) in the cytoplasm and synthesizing pentoses and a few other sugars. It also provides a means of converting pentoses and certain other sugars into intermediates of the glycolytic pathway. It proceeds from d-glucose 6-phosphate to d-ribulose and d-ribose phosphates, thence (with d-xylulose 5-phosphate) to d-sedoheptulose 7-phosphate and d-glyceraldehyde 3-phosphate; carbon dioxide is released in the gluconate-ribulose step. In plants, it participates in the formation of d-glucose from carbon dioxide in the dark reactions of photosynthesis. This pathway is defective in certain inherited diseases, for example, glucose-6-phosphate dehydrogenase deficiency.
Farlex Partner Medical Dictionary © Farlex 2012
pentose phosphate pathway (PPP), pentose phosphate shunt, hexose monophosphate shunt or phosphogluronate pathway a PATHWAY for the metabolism of glucose. PPP is particularly important in animal cells where it functions as an alternative to GLYCOLYSIS and the KREBS CYCLE, although both mechanisms occur together.
In the PPP, glucose (a hexose sugar) in the form of glucose phosphate molecules, is oxidized by the removal of hydrogen and decarboxylated, producing pentose sugars, carbon dioxide and hydrogen atoms, which are transferred to the coenzyme NADP to form NADPH2. In a second stage the pentose sugars are rearranged to produce hexose again, although in a smaller quantity than at the start. Unlike NADH, NADPH is not involved in producing ATP via an ELECTRON TRANSPORT SYSTEM, but transfers hydrogen atoms and electrons to sites where molecules are being assembled.
The NADPH2 molecules are particularly active in cells carrying out fat metabolism, such as adipose tissue, liver, adrenal cortex, mammary gland tissue.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005