 |
| Glandular Epithelium |
Glandular epithelium is composed of cells that are specialized to manufacture and secrete various substances into ducts or into body fluids. Such glandular cells are usually found within columnar or cuboidal epithelium, and one or more of them constitutes a gland. Those glands that secrete their products into ducts that open onto some internal or external surface are called exocrine glands.
Those that secrete into tissue fluid or blood are called endocrine glands.
Although a gland may be a single cell (unicellular gland), most glands are composed of many cells (multicellular gland). These more complex glands can be classified according to the arrangement of their epithelial cells. For example, exocrine glands that consist of simple epithelial-lined tubes opening to the surface are called tubular glands, while those that are composed of one or more saclike dilations connected to the surface by narrowed secretion ducts are called alveolar glands.
Glandular secretions are classified according to whether they consist of cellular products or portions of the glandular cells Glands that release fluid cellular products through cell membranes Without the loss of cytoplasm are called mtvm glands. Those that release entire cells filled with secretory products are called holocrine glands, while those of an intermediate type that lose small portions of their glandular cell bodies during secretion arc called apocrine glands.
Most secretory cells are merocrine, and they can be further subdivided as either serous cells or mucous cells. The secretion of serous cells is typically watery and has a high concentration of enzymes.
Such cells are common in the glands of the digestive tract Mucous cells secrete the thicker fluid called mucus. This substance is rich in the glyco-protein mucin and is secreted abundantly from the inner linings of the digestive and respiratory tubes.
0 comments:
Post a Comment