Ultrastructural studies of normal skin and epidermal papillomas of the flathead sole, Hippoglossoides elassodon

Morphology of the buccopharyngeal portion of the gill in the fathead minnow Pimephales promelas (Rafinesque)

Buccopharyngeal epithelium covering gill arches and gill rakers of the fathead minnow was studied by light microscopic, scanning, and transmission electron microscopic techniques. Mature mucous cells in goblet pattern and nonmucus containing cells were in the apical one-third of the tissue. The latter cells contributed to a surface microridge system which overlapped apices of goblet cells. The bottom of the epithelium was comprised of a continuous row of darkly stained basal epithelial cells. In this region, two to three epithelial cells of similar staining characteristics were piled up forming apical columns which partially encircled nests of lightly stained cells. A basal lamina and thick basement lamella of about 20 piles of orthogonally arranged collagen supported the epithelium. Numerous taste buds were seen in gill arches and rakers. Taste bud cellular components included marginal cells, light receptor cells, dark receptor cells, and basal cells. These were identical in all taste buds. Taste bud surface morphology differed between gill arch and raker. Pores of the former were depressed, while those of the latter were raised. Thick microvilli of taste pores were apical extensions of light cells, while smaller, more numerous microvilli were projections from dark cells.

Mucosaccharide histochemistry and histoenzymorphologic observations on the epidermis of Ariosoma balearicum de la Roche (Anguilliformes, Pisces)

The epidermis of Ariosoma balearicum consists of three layers - the basal layer, the middle layer and the outer layer. In between the basal cells are found clusters of small lymphocytes which show a moderat acid phosphatase activity. The middle layer and the outer layer are composed of three types of cells - the polygonal cells, the mucous cells and the club cells. The mucosubstances within the mucous cells exhibit the properties of neuraminic acid containing mucosaccharides with vicinal hydroxyl, sulfate esters and carboxyl groupings. The superficial cells of the outermost layer are capable of secreting sulphated and carboxylated mucosubstances to form an extracellular mucous coating which in fish epidermis seems to be necessary for the accumulation of electrolytes. The club cells are generally provided with one nucleus or double nuclei which appear displaced from the center and constitute the main histological component of the middle layer. The contents of these cells, in addition to a strong protein uptake visualized by the positive reactions exhibited in the coupled tetrazonium and mercuric bromophenol blue preparations, gave positive response to neutral mucosubstances which appear to be a glycoprotein involved in the slime secretions. Alkaline phosphatase and TPP-hydrolysing enzyme which could be detectable in the basal layer and the basement membrane were correlated with the probable role that they could play in the transportation of various chemicals and nutriments through the cell membranes.

A proposed function for microridges on epithelial cells

Microridges (MR), also called microvillar ridges, microplicae and cytoplasmic folds, have been noted on many epithelial surfaces. Several functions have been proposed for these structures. In the present study we examine the mechanical role that microridges may play in holding mucus to the lumenal surface to the esophagus in the trout Salmo gairdneri. Our findings support the hypothesis that the microridges help hold a protective coat of mucus to the epithelium. In addition, the complex curved or whorled arrangement of microridges appears to facilitate the spread of mucus away from goblet cells.