The Capillary Endothelium in the Rete Mirabile of the Swimbladder of the Eel (Anguilla anguilla): Functional and Ultrastructural Aspects

Abstract

The rete mirabile of the swimbladder of the eel is a network of straight capillaries, one against the other, in which an arterial capillary alternates with a venous capillary. The function of these capillaries is to allow the swimbladder to concentrate oxygen by a hairpin countercurrent multiplication mechanism.Electron microscopy shows a very large number of channels in the endothelial cells and most of the channels have alternating dilatations and constrictions as though fixed in a condition of peristalsis. The findings suggest that there is a continuity between the organelles and indicate that the hairpin countercurrent multiplication mechanism may be dependent upon a continuous active return system composed of the membrane-bound channels.