countercurrent exchange

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countercurrent exchange

a biological mechanism designed to enable maximum exchange between two fluids. The mechanism's effect is dependent on the two fluids flowing in opposite directions, and having a concentration gradient between them.

fluid ONE

high concentration → low concentration

fluid TWO

high concentration ← low concentration

Such mechanisms occur, for example, in oxygen exchange between water and the blood vessels in fish gills, and in the ascending and descending tubules of the LOOP OF HENLE in the mammalian kidney.

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
References in periodicals archive ?
Architecture of inner medullary descending and ascending vasa recta: pathways for countercurrent exchange. Am.
(1995) studied experimentally the buoyant countercurrent exchange flow through a vented horizontal partition using a two-component laser doppler velocimeter.
The arrangement of the tubule vasculature helps the nephrons concentrate or dilute fluid by creating a countercurrent exchange between the solute and water-rich fluid within the tubule (coming from the Bowman's capsule) and the solute-and water poor descending vasa recta (and proximal capillaries) coming from the glomerulus.