The microanatomy of the rectal salt gland of the Port Jackson shark, Heterodontus portusjacksoni (Meyer) (Heterodontidae): Suggestions for a counter-current exchange system

A comprehensive anatomical study was undertaken to examine the rectal salt gland in the Port Jackson shark, Heterodontus portusjacksoni, a shark known to invade estuarine environments. The microstructure and vascular organisa tion of the rectal salt gland was investigated using histological observati on and scanning electron microscopy of vascular corrosion casts. Cellular s pecialisation was observed in the lining of the central lumen of this gland , This may indicate that there is some modification of the principal produc t of the gland prior to its secretion. The rectal salt gland has a complex structure related to its function. Contrary to previous reports, the flow i n secretory tubules is in the opposite direction to that of the capillaries and thus constitutes a counter-current arrangement. The similarity in the organisation of the counter-current and lobulate arrangement of salt-secret ing glands through phylogenetically diverse organisms, such as sharks and b irds, suggests that this arrangement is important in achieving efficient sa lt secretion. Copyright (C) 2001 S.KargerAG, Basel.