CHARACTERISTICS OF THE GLANDULAR EPITHELIUM
The glandular epithelia or secretory epithelia are a division of the Epithelial Tissue which specialized in cellular secretion.
Secretion is being used here in its broadest sense, which includes:
- synthesis of new molecules from smaller precursors – e.g., protein synthesis.
- modification of preexisting molecules – e.g., secretion of steroids.
- transport of ions – e.g., secretion of sweat and part of the saliva.
Being a division of the Epithelial Tissue, the glandular or secretory cells have all the characteristics of epithelial tissue cells, among which the following stand out:
- Great proximity and adhesion between cells.
- Small amount of extracellular matrix between the cells.
- Polarity of cells.
- The cells are supported by a basal lamina.
Arrangement of the secretory cells:
Unlike the cells of the covering epithelia, the glandular epithelia are vey often arranged as single layers of cells. These layers, however, are not flat like in the covering epithelia. They generally assume three-dimensional arrangements, constituting the glands.
Secreting epithelia
The division of Epithelial Tissue into two categories, however, does not mean that a lining epithelium cannot also secrete. See two examples:
– In the previous chapter, secretory cells were shown inserted between the cells of a lining epithelium – the goblet cells, found in the respiratory epithelium, were interspersed between the lining cells. Goblet cells are also present in large quantities in the epithelium of the intestinal mucosa forming tubular glands.
– All cells of the simple prismatic epithelium that lines the inside of the stomach cavity are secretory.
How are secretory cells organized?
As shown, secretory epithelial cells can assume several types of arrangements:
- Stay individually among other cells (e.g.: goblet cells).
- Form a lining epithelium that is also secretory (such as the covering epithelium of the stomach mucosa).
- Combining into associations of different sizes, forming separate, individual specialized secretory structures or entire organs, which are called glands.