MAIN FEATURESS OF GLANDULAR EPITHELIA
Glandular or secretory epithelium is a type of epithelial tissue specialized for the production of molecules and the transport of various ions.
Here, secretion is used in its broadest sense and includes:
- Synthesis of new molecules from smaller precursors such as protein synthesis.
- Modification of preexisting molecules such as secretion of steroids.
- Transport of ions such as the in secretion of sweat and saliva and during the production of urine.
Because glandular or secretory cells are a type of epithelial cell, they share many of the general characteristics of epithelial tissue described in Chapter 2. The main characteristics include:
- Close proximity and strong adhesion between cells.
- Cell polarity, with different cell regions having different structures and functions.
- Support by a basal lamina which, is usually associated with variable amounts of underlying connective tissue.
Arrangement of Secretory Cells
Glandular epithelial cells may be organized in several ways. They may occur as individual cells, as single layers of cells, or as clusters and more complex three-dimensional structures of various sizes.
Secretory Activity in Lining Epithelia
The division of epithelial tissue into lining epithelium and glandular epithelium does not mean that lining epithelia lack secretory activity. In fact, many lining epithelia contain secretory cells or have cells that secrete substances.
Two examples are:
– Goblet cells in the respiratory epithelium are secretory cells interspersed among the other cells of a lining epithelium. Goblet cells are also abundant in the epithelium of the intestinal mucosa, where they secrete mucus.
– Most cells of the simple epithelium lining the stomach lumen are secretory and contribute to the production of the substances released into the stomach.
How Are Secretory Cells Organized?
Secretory cells can be organized in several ways::
- As individual cells, such as goblet cells, interspersed among the other cells of a lining epithelium. These are called unicellular glands.
- As part of a lining epithelium that is itself secretor, as in the epithelium lining the stomach mucosa.
- As multicellular glands, in which many secretory cells are organized into structures of various sizes and shapes. These structures may form three-dimensional glands or, in some cases, constitute entire organs.