The fine structure of the secondary lamellae of the gills of Gadus pollachius

Abstract

ABSTRACT The structure of the leaf-like secondary lamellae, across which gaseous exchange takes place, is described on the basis of an electron-microscope study of sectioned material. The epithelial layers on the two sides of the secondary lamellae are separated by widely spaced pillar cells, of characteristic form. These have a central cell body with wide flanges at each end which spread out below the epithelia. The flanges of adjacent pillar cells meet and connect, delimiting an extensive blood space between the pillar cell bodies. Pillar cells contain abundant mitochondria and membranes, and their cytoplasmic matrix is largely occupied by finely fibrous material. They appear to be responsible for the formation of a thick, collagen-containing basement membrane which lies between them and the overlying epithelia. There are also columns of basement membrane material which run transversely across the secondary lamellae, set in deep infoldings in the surface of the pillar cell bodies. Pillar cells appear to combine the functions of fibroblasts and the endothelial cells of true capillaries. The epithelium forming the outer surface of the secondary lamellae is one or more cells thick and consists of cells with large nuclei and abundant mitochondria and cytoplasmic membranes. The water/blood pathway across which gaseous exchange takes place consists of the epithelium, basement membrane and pillar cell flange and has a total thickness of 1 to 3μ.