Exocrine secretion

The exocrine secretion is the delivery of a secretion to the inner or outer surface. This type of secretion occurs, for example, in the sweat or salivary glands. Sjogren's syndrome is an example of diseases that destroy the exocrine glands.

What is Exocrine Secretion?

The main task of glands is the secretion of bioactive substances such as hormones or growth factors. Different forms of glands occur in the human body. A major distinction is that between incretory and excretory glands. Excretory glands secrete to the inner or outer surface. Incretory or endocrine glands secrete into the extracellular space. Before the exocrine secretion, the substrate is first synthesized in the glands.

Exocrine glands are excretory glands that release their secretions to the surface. Exocrine secretion can take place in a number of ways. In addition to eccrine and apocrine secretion, holocrine and apical secretion are also considered secretion modes for exocrine glands.

Exocrine glands include, for example, the sweat glands, the mammary glands, the pancreas or the liver. The salivary glands or the sebum glands are also exocrine glands. In addition to exocrine secretion in the duodenum, the pancreas is also involved in endocrine secretion. In addition to the secretion mode, exocrine glands can be further differentiated according to their type of secretion and their structure.

Function & task

With excretory secretion, exocrine glands release a secretion to the surface. The glands are usually located in the epithelium of the connective tissue and have an outlet duct. During embryonic development, exocrine glands migrate from the epithelial surface into the depths of the tissue.There they differentiate into organs with typically specialized epithelial cells. They remain networked with the epithelial surface.

Exocrine glands are either intraepithelial or extraepithelial. The intraepithelial glands correspond to individual or group-like cell formations that lie in the epithelium, as is the case, for example, for the mucin-producing cells in the mucous membranes.

Extraepithelial glands are more complex. They lie under the surface epithelium of the connective tissue and are made up of a single-layer epithelium for secretion formation and an outlet duct into the surface epithelium. The exocrine ducts sometimes change the composition of the secretion in exocrine secretion and thus turn a primary secretion into a secondary secretion. This applies, for example, to ion reabsorption by the sweat glands.

Depending on their end pieces, exocrine glands are tubular, acinous, alveolar, or mixed. Tubular end pieces have a tubular lumen. Acinous end pieces are spherical and alveolar end pieces have a clearly visible vesicle shape.

Depending on their duct system, exocrine glands are either single, branched, mixed, or compound. If there is no or only one unbranched duct, the gland is called 'simple'. It is called 'branched' when there are several end pieces and medicine speaks of 'compound' glands in the case of a branched duct system. Mixed glands are compound glands with multiple types of end pieces.

Depending on their secretion, the glands are either serous, mucous, or seromucous. Serous glands have a thin, proteinaceous secretion. Mucosal glands synthesize viscous mucin-rich secretions and seromucous glands are mixed glands with a secretion between serous and mucous.

Eccrine, merocrine, apocrine and holocrine secretion are available as modes of exocrine secretion. In the eccrine mode, the gland secretes without loss of cytoplasm. Merocrine exocrine secretion is a secretion with little loss of cytoplasm and with apocrine secretion parts of the cell and the cell membrane are released with the secretion. In the case of holocrine glands, the entire cell disintegrates during secretion. An example of this are the sebum glands.

The secretion is produced in the glandular bodies of exocrine glands. The synthesis and secretion are subject to complex control loops, the best known of which is the ultrashort feedback mechanism.

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Illnesses & ailments

The human secretion system is interconnected within itself. If, for example, the exocrine secretion of a single gland is disturbed, the endocrine secretions can be unbalanced and vice versa. For this reason, glandular diseases usually show a particularly wide range of symptoms.

In addition to growth and development processes, they can unbalance metabolic processes and hormonal levels or develop into a multi-organ disease. An example of disturbed exocrine secretion is exocrine pancreatic insufficiency. This is a loss of function of the pancreas, which disrupts the production of digestive enzymes. The digestive enzymes secrete the pancreas through exocrine secretion into the duodenum. Since it is also responsible for endocrine secretion as a gland, a complete loss of function of the pancreas also affects the hormonal balance. In addition to blood sugar disorders, the most obvious symptoms of this disease are digestive problems such as diarrhea. Pancreatic insufficiency is often preceded by chronic inflammation of the pancreas, which initially only affects the exocrine functions and thus disrupts digestion.

All other exocrine glands can also be affected by a loss of function and thus only perform insufficient exocrine secretion. In cystic fibrosis, the exocrine secretion of all excretory body glands is disturbed. This disease is an inherited disorder of the autosomal recessive inheritance that causes a mutation on the autosomal chromosome 7. The mutated CFTR gene results in a pathological gene product. The encoded chloride channels of the gene are therefore not functional. Because of the faulty chloride channels, tough mucus forms in all exocrine glands.

Autoimmune diseases can also affect exocrine secretion. An example of incorrect programming of the immune system with consequences for the exocrine glands is Sjogren's syndrome, in which the exocrine gland system is immunologically destroyed.