The Microvascular Organization of the Gas exchange Organs of the Australian Lungfish, Neoceratodus forsteri (Krefft)

Abstract

The general organization of the gill microvasculature of Neoceratodus is similar to that reported for elasmobranchs. A corpus cavernosum is situated between the afferent filamental artery and afferent lamellar arterioles. The microvascular network of the lamellar blood sheet consists of a series of major channels, curving in concentric arcs from afferent to efferent lamellar arterioles, with minor radial cross-connections between these major channels; the basal lamellar channels are not buried in the filament. The afferent filamental arteries also supply blood to the interbranchial septum, which extends almost to the filament tip. The water-blood barrier of 3-4 µm consists of up to three cells: the surface epithelial cell, the pillar cell flange. plus a frequently interposed interstitial cell; there is a prominent basal lamina immediately external to the pillar cell flange. Adjacent gill secondary lamellae are commonly fused at their free margins near the leading edge into groups of from two to five. The micro-organization of the pseudobranch is in general similar to that of the posterior holobranchs. The lung is divided into a series of air sacs by stout septae which contain large amounts of smooth muscle. The respiratory epithelium is of two types: a squamous epithelium underlain by a dense capillary sheet, and isolated patches of a columnar muco-ciliary epithelium associated with only few capillaries. The air-blood barrier (approximately 3 µm thick) consists of a squamous epithelial cell process and attenuated vesiculated endothelial cell cytoplasm, with two basal laminae and intervening interstitial space situated between these.