Apical cytoplasm

About: Apical cytoplasm is a research topic. Over the lifetime, 1080 publications have been published within this topic receiving 36131 citations.

Fine Structure of Duvernoy's Gland of the Japanese Colubrid Snake, Rhabdophis tigrinus

Abstract: Duvernoy's gland (a type of venom gland) of the Japanese colubrid snake, Rhabdophis tigrinus, was examined by electron microscopy. The secretory units of the gland consist of the secretory and myoepithelial cells. The secretory cells are columnar in shape and have well-developed rough endoplasmic reticulum (RER), Golgi apparatus and mitochondria in the basal perinuclear cytoplasm. The secretory granules are homogeneous in structure and moderately dense. They are accumulated in the apical cytoplasm and are released by exocytosis into the lumen. The myoepithelial cells often enclose the secretory units, contain bundles of filaments in the cytoplasmic process, and are innervated by the free endings of the autonomic nerves through the basement membrane. In addition, many nerve terminals end in pericapillary spaces, suggesting a release of neurosecretions into the blood. The duct epithelium is composed of typical mucus secreting cells, whose cytoplasm contains secretory globules of lower electron density.

Morphological and histochemical observations on the duodenal glands of eight wild ungulate species native to North America.

Abstract: The duodenal glands of the species examined (Alces alces, Ovis canadensis, Cervus canadensis, Oreamnos americanus, Bison bison, Antilocapra americana, Odocoileus virginianas, Odocoileus heminous) are confined primarily to the submucosa of the small intestine. In one species, the moose, a significant population of secretory tubules also is observed in the mucosa. The ducts of the duodenal glands pierce the overlying muscularis mucosae to empty most often independently into the intestinal lumen. Those of the bison, unlike the other species examined, drain into intestinal glands. The duodenal glands consist primarily of a simple columnar epithelium, the cells of which contain basally positioned round or oval nuclei. The lumina of scattered duodenal glands in the pronghorn and to some extent those of the moose, white-tailed deer, and mule deer may be extremely dilated, and the surrounding epithelium thin and attenuated. Component cells of the duodenal glands of all the species examined show remarkably similar ultrastructural features. They exhibit scattered profiles of rough endoplasmic reticulum, dilated cisternae of which contain an electron-dense, amorphous material. Numerous well-developed Golgi complexes occupy the supranuclear region together with transport vesicles and forming secretory granules. Electron-dense, membrane-bound secretory granules generally are concentrated in the apical cytoplasm immediately subjacent to the cell membrane. The apical cell membrane exhibits short, scattered microvilli; and the basal cell membrane is smooth without apparent specialization. Histochemically, the duodenal glands of most species examined in this study consist of a heterogeneous population. The majority of the glands of the moose, elk, mountain goat, bison, pronghorn, and white-tailed deer elaborate a neutral mucin, whereas scattered individual glands, tubules or cells also produce acid mucins. Cells near the terminations of the ducts of the bighorn sheep are the only elements to produce acid mucins in the duodenal glands of this species. The duodenal glands of the bison are unusual in that only the peripheral portions of individual glands produce acid mucins. The remainder of the glands elaborate neutral mucins. Morphological differences between the two regions were not observed. The duodenal glands of the mule deer secrete both acid and neutral mucins. The structural and histochemical observations appear unrelated to the diet of individual species.

Electron microscopic observations on the yolk sac of the Indian fruit bat, Rousettus leschenaulti (Desmarest) (Pteropidae).

Abstract: The yolk sac of the Indian fruit bat Rousettus leschenaulti is unique since during the course of development it become converted into a solid, richly vascular endocrine gland-like structure with both the endodermal and mesothelial cells undergoing substantial hypertrophy. The yolk sac is progressively drawn from the abembryonic (antimesometrial side) to the embryonic pole (mesometrial side) of the chorionic sac where in late stages it comes to rest against the placental disc. The endodermal cells become grouped into clusters of acinus-like structures surrounded by the columnar mesothelial cells; the yolk-sac lumen is in most instances obliterated. Individual endodermal cells are large in comparison to mesothelial cells. The endodermal cell population varies between cells with abundant agranular ER and areas devoid of organelles to others with dense cytoplasm containing stacks of granular ER. All endodermal cells have numerous mitochondria and a few lipid droplets. The mesothelial cells are columnar with either dome-shaped, pointed or flattened apices bearing numerous elongate microvilli; within these are parallel-arranged microfilaments. While the apical cytoplasm shows the presence of absorptive tubules. coated vesicles and caveolae, the basal cytoplasm contains a few small mitochondria. Some mesothelial cells contain lipid droplets in their basal cytoplasm. On structural bases it is postulated that the mesothelial cells are absorptive in function while the endodermal cells are synthetic and secretory.

A fine structural study of the highly active thyroid follicular cell of the African basenji dog.

Abstract: The highly active thyroid gland of the basenji dog has been studied. The follicular cell of the basenji thyroid is unusual in that colloid droplets may be found in the apical cytoplasm of normal cells. Their appearance does not require administration of exogenous thyrotrophin. The colloid droplets appear to have been taken in by invagination of the apical plasma membrane forming a small bay at the cell-colloid interface. Apparent fusion of adjacent plasma membranes subsequently eliminates the mouth of the bay, completing endocytosis of the droplet. Basenji follicular cells are also distinguished by a dense accumulation of two varieties of lysosomes, basal associations of lip d droplets and mitochondria with unusual cristae and specialized junctions between cells of adjacent follicles. It is suggested that these unique structural modifications reflect adaptations for the perpetually active state of the basenji thyroid.