Exocrine secretion is the release of a secretion to the internal or external surface. This type of secretion is present, for example, in the sweat or salivary glands. Sjögren’s syndrome is an example of diseases that destroy the exocrine glands.
What is exocrine secretion?
Exocrine secretion is the release of a secretion onto the internal or external surface. This type of secretion is present, for example, in the sweat or salivary glands. The main function of glands is the secretion of bioactive substances such as hormones or growth factors. Various forms of glands occur in the human body. One main distinction is between incretory and excretory glands. Excretory glands secrete to the internal or external surface. Incretory or endocrine glands secrete into the extracellular space. Prior to exocrine secretion, the substrate for this is first synthesized in the glands. Exocrine glands are excretory glands that secrete their secretion to the surface. Exocrine secretion can occur in a variety of ways. In addition to eccrine and apocrine secretion, holocrine and apical secretion are also considered secretory modes of exocrine glands. For example, the sweat glands, the mammary glands, the pancreas, or the liver are considered exocrine glands. The salivary glands or the sebaceous glands are also exocrine glands. The pancreas is involved in endocrine secretion in addition to exocrine secretion into the duodenum. Exocrine glands can be further distinguished according to their secretion mode and their construction, in addition to their secretion mode.
Function and task
In excretory secretion, exocrine glands secrete a secretion to the surface. The glands are usually located in the epithelium of the connective tissue and have an excretory duct. During embryonic development, exocrine glands migrate from the epithelial surface down into the depths of the tissue. There they differentiate into organs with typically specialized epithelial cells. They remain interconnected with the epithelial surface. Exocrine glands are either intraepithelial or extraepithelial. Intraepithelial glands correspond to single or lobule-like cell formations located in the epithelium, as is true, for example, of mucin-producing cells in mucous membranes. Extraepithelial glands have a more complex structure. They lie beneath the surface epithelium of the connective tissue and are composed of a single-layered epithelium for secretion formation and an excretory duct into the surface epithelium. The excretory ducts sometimes alter the secretion composition during exocrine secretion, thus turning a primary secretion into a secondary secretion. This is true, for example, in the ion reabsorption of the sweat glands. Depending on their terminals, exocrine glands are tubular, acinar, alveolar, or mixed. Tubular terminals have a tubular lumen. Acinar terminals are spherical and alveolar terminals have a highly visible vesicular shape. Depending on their excretory duct system, exocrine glands are either simple, branched, mixed, or compound. With no or only one unbranched excretory duct, the gland is called ‘simple’. ‘Branched’ is the name given to it when there are multiple terminals, and ‘compound’ glands are referred to by medicine when there is a branched excretory duct system. Mixed glands are compound glands with several types of terminals. Depending on their secretion, glands are either serous, mucous or seromucous. Serous glands have a thin proteinaceous secretion. Mucous glands synthesize viscous mucin-rich secretions, and seromucous glands are mixed glands with a secretion between serous and mucous. Modes of exocrine secretion include eccrine, merocrine, apocrine, and holocrine. In the eccrine mode, the gland secretes without cytoplasmic loss. Merocrine exocrine secretion is secretion with little loss of cytoplasm and in apocrine secretion, parts of the cell and cell membrane are released with the secretion. In holocrine glands, even the entire cell disintegrates during secretion. An example of this is the sebaceous glands. In the gland bodies of exocrine glands, the secretion is produced. Synthesis and secretion are subject to complex regulatory circuits, the best known of which is the ultrashort feedback mechanism.
Diseases and disorders
The secretory system in humans is intrinsically cross-connected.For example, if the exocrine secretion of a single gland is disturbed, the endocrine secretions can also become unbalanced and vice versa. For this reason, glandular diseases generally exhibit a particularly broad range of symptoms. In addition to growth and development processes, they can unbalance metabolic processes and hormone levels or develop into a multi-organ disease. An example of disturbed exocrine secretion is exocrine pancreatic insufficiency. This is defined as a loss of function of the pancreas that interferes with the production of digestive enzymes. The pancreas secretes the digestive enzymes into the duodenum by means of exocrine secretion. Since, as a gland, it also carries out endocrine secretion, a complete loss of function of the pancreas also shows effects on hormone balance. The most obvious symptoms of this disease, in addition to blood sugar disturbances, are digestive complaints such as diarrhea. Pancreatic insufficiency is often preceded by chronic inflammation of the pancreas, which initially only impairs exocrine functions and thus disrupts digestion. All other exocrine glands may also be affected by loss of function, resulting in inadequate exocrine secretion. In cystic fibrosis, exocrine secretion of all excretory body glands is impaired. This disease is a hereditary disease of autosomal recessive inheritance, which causes a mutation on autosomal chromosome 7. The mutated CFTR gene results in a pathological gene product. The encoded chloride channels of the gene are therefore non-functional. Due to the defective chloride channels, viscous mucus forms in all exocrine glands. Autoimmune diseases can also affect exocrine secretion. An example of immune system misprogramming with consequences for the exocrine glands is Sjögren’s syndrome, in which the exocrine glandular system is immunologically destroyed.
