The delicate and elaborate structure of the fish gill has long fascinated biologists as perhaps the most exquisite example of an external respiratory organ. The pioneering work of Krogh, and later Maetz, clearly showed that the gill was also the major osmoregulatory organ in these vertebrates and Smith added yet another dimension, nitrogen excretion, to gill function. Additional work has since demonstrated that acid-base regulation and detoxification are also mediated by branchial tissues (see, Hoar and Randall, 1984a, b for an excellent compilation of reviews on gill anatomy and physiology). It thus became apparent that the gill was a multifunctional organ engaging in a number of seemingly unrelated homeostatic activities whose only common feature was transepithelial exchange between internal and external milieu. Morphological studies have revealed a number of distinct cells in gill tissue and numerous attempts have been made to correlate cell type with function (see below). An interesting, and perhaps not unexpected, finding from these studies was that specific cells are grouped into discrete areas within the gill and thus gill tissues are organized into anatomical, and probably functional units. The most obvious common modality between these anatomical units is the vasculature that perfuses them. Recent studies have shown that the gill circulation forms one of the most complex vascular networks found in any vertebrate and that it may, through vasoactive mechanisms, have considerable impact on gill function. Furthermore, the extensive gill vascular surface area and the in-series position of the gill and systemic circulations provide the gill with a unique opportunity to metabolize plasma-borne molecules and thus adds an additional regulatory role to the branchial tissues.
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)