Morphology of the exocrine glands of the frog skin

Abstract

Frog skin contains three distinct types of exocrine glands: granular (poison), mucous, and seromucous. The granular gland forms a syncytial secretory compartment within the acinus, which is surrounded by smooth muscle cells. The mucous and seromucous glands are easily identifiable as distinct glands. The serous and mucous secretory cells are arranged in a semilunar configuration opposite the ductal end and are filled with granules. Within the acinus, located at the ductal pole of the gland, are distinct groups of cells with few or no granules in the cytoplasm. In both the mucous and seromucous gland there is a cell type with abundant mitochondria; the one in the mucous gland is located in the region adjacent to the secretory cells. The duct of these glands is two-layered, with the individual cells appearing morphologically similar to the layers of the skin epithelium as the duct traverses the skin. The duct appears to be patent throughout its length. The morphological heterogeneity and distinct distribution of the cell types within the gland acinus may be indicative of a functional heterogeneity that allows the production of distinctly different types of secretion from the same gland type, depending on the type of stimulus.

Comparative analysis of the integument of different tree frog species from Ololygon and Scinax genera (Anura: Hylidae)

“…They have been described as being of different types, like mucous, serous, lipid (or wax), and mixed (seromucous) glands. However, some authors have named the granular glands as poison or serous glands (Mills and Prum 1984, Duellmann and Trueb 1994.…”

Involvement of Rel factors in the expression of antimicrobial peptide genes in amphibia

“…The secretion can be collected easily following mild electrical stimulation of the animal and the presence of antimicrobial peptides can be analysed qualitatively and quantitatively. Moreover, because these glands release the secretory materials via a holocrine mechanism [19], analysis of released proteins can provide additional information on the regulatory mechanisms that form the basis of the innate immune defence, avoiding animal killing.…”

Molecular and cellular characterization of a new aquaporin, AQP-x5,specifically expressed in the small granular glands ofXenopusskin

“…Mills and Prum (Mills and Prum, 1984) further subdivided the mucous glands of Rana pipiens, R. temporaria and R. catesbeiana as being either mucous or seromucous glands, whereas Fujikura et al (Fujikura et al, 1988) distinguished between the small granular gland and the granular and mucous glands. However, MR cells interspersed with secretory cells are commonly present only in Xenopus small granular glands (Fujikura et al, 1988) and in the mucous glands of R. pipiens, R. temporaria and R. catesbeiana (Mills and Prum, 1984). Furthermore, the secretory activity of the serous glands is stimulated in response to isoproterenol, which is a ␤-adrenergic agonist, whereas that of the small granular glands and mucous glands is not (Fujikura et al, 1988).…”