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The brush border on the apical surface of the epithelial cells is covered with glycocalyx, which is composed of oligosaccharides attached to membrane glycoproteins and glycolipids. [7] TEM image of a thin section cut through an epithelial cell showing the luminal surface (apical end) of the cell packed with microvilli that make up the absorbing ...
The basal surface of epithelial tissue rests on a basement membrane and the free/apical surface faces body fluid or outside. The basement membrane acts as a scaffolding on which epithelium can grow and regenerate after injuries. [16]
Microvilli on the apical surface increase its surface area. This facilitates transport of numerous small molecules into the enterocyte from the intestinal lumen . These include broken down proteins , fats , and sugars , as well as water, electrolytes , vitamins , and bile salts .
These are known as non-ciliated columnar epithelium. Non-ciliated simple columnar epithelium is made up of glandular goblet cells which secrete mucin to form mucus. [1] The rest of the cell is made up of cytoplasm with membrane bound secretory granules which secrete the mucin, and are found towards the apical surface of the cell. [1]
Sometimes apical is used exclusively for an articulation that involves only the tip of the tongue and apicolaminal for an articulation that involves both the tip and the blade of the tongue. [3] However, the distinction is not always made and the latter one may be called simply apical, especially when describing an apical dental articulation.
The sharp distinction between apical and baso-lateral domains is maintained by an active mechanism that prevents mixing. The nature of this mechanism is not known, but it clearly depends on the polarity determinants. In the absence of the aPKC complex, the baso-lateral determinants spread into the former apical domain.
The apical portion is shaped like a cup, as it is distended by abundant mucus laden granules; its basal portion lacks these granules and is shaped like a stem. The goblet cell is highly polarized with the nucleus and other organelles concentrated at the base of the cell and secretory granules containing mucin, at the apical surface. [1]
The membrane is made up of a hexagonal lattice put together in the Golgi apparatus and implanted into the surface of the cell by reverse pinocytosis, a type of exocytosis. [8] The cells in the superficial layer of the transitional epithelium are highly differentiated, allowing for maintenance of this barrier membrane. [8]