Types of exocrine glands according to morphological features
Glands can be classified according to the morphology of the secretory part. Tubular or tubuloacinar glands show tube-like secretory portions. The secretory part may be not straight but curved (for example, sweat glands of the skin). Alveolar glands contain secretory parts resembling rounded bags. Acinar cinar glands show pear-like secretory portions (for example, urethral, periurethral and paraurethral glands).
Independently of the shape of the secretory portion, simple glands contain an unbranched excretory duct and one secretory unit, whereas simple branched glands are formed by several secretory units that release their products to the same excretory duct. Typical examples of a simple gland are the sweat glands of the skin, which are tubular. Peri- and paraurethral glands are simple acinar glands. In the stomach, simple branched acinar glands (mucous glands of the stomach cardia) and simple branched tubular glands (mucous glands of the pylorus) can be found.
Compound glands are the more complex glands. The excretory duct is branched and may contain many secretory units. The main excretory duct releases the secretory product to the body surfaces and gives rise to branches known as interlobular ducts. Every interlobular duct collects secretory products from the gland lobules. Lobules can be observed without microscope. Inside every lobule, there are intralobular ducts that can also be branched. In the lobule, the secretory units of the gland are found at the end of the smaller intralobular ducts. A compound gland may have secretory units showing different morphology. For example, acinar and tubular secretory units can be observed in the so called tubulo-acinar glands (not shown in the table). Connective tissue can be found around ducts and secretory units, where blood vessels and nerves can also be found.
Examples of compound glands: exocrine pancreas is an acinar compound gland; Brunner glands of the duodenal submucosa are tubular compound glands; mammary gland, lacrimal gland and submandibular salivary gland are tubulo-acinar compound glands.