As early as 1686 , the Italian anatomist Marcello Malpighi had defined glands as “closed caves with one duct” .
According to location
- intraepithelial glands: individual or small groups of cells embedded in the epithelium . An example of this are the mucin-producing cells of the mucous membranes .
- extraepithelial glands: more complex glands located in the connective tissue under the surface epithelium. They consist of end pieces producing secretion (single-layer epithelium), which open directly or with an excretory duct (partially multilayered epithelium) into the surface epithelium. In some glands the ducts change the composition of the primary secretion to the finished secondary secretion; an example of this is ion reabsorption in the ducts of human sweat glands .
According to the shape of the end pieces
- tubular: tubular; small lumen that can still be seen under a light microscope
- acinous: approximately spherical; Lumen not visible under a light microscope
- alveolar: vesicular; large lumen easily recognizable with a light microscope
- Mixed forms: tubuloacinous , tubuloalveolar
According to the execution corridor system
Among the extraepithelial glands only the tubular glands appear, even without ducts.
simple: A gland is called simple if it has no duct or an unbranched duct.
- branched: Simple glands that contain several end pieces are referred to as branched.
compound: A gland is called compound if it has a branched duct system.
- mixed: Mixed are those compound glands that contain several types of end pieces.
According to the consistency of the secretion
- Serous : Serous glands produce thin, often protein-rich secretions and usually have acinous end pieces. (Examples: parotid gland , exocrine pancreas , lacrimal gland (glandula lacrimalis))
- Mucous: Mucous glands produce viscous, mucin- rich secretion and have tubular end pieces. (Examples: gland on the cervix , Brunner's glands of the duodenum , glands in the pharynx and on the root of the tongue, Cowper's gland on the urethra of male individuals)
- seromukös or mukoserös: seromucous glands combine properties of serous and mucous glands and are mixed glands. (Examples: mandibular and sublingual salivary glands )
- Renate Lüllmann-Rauch: pocket textbook histology. 4th edition. Thieme, 2012, ISBN 978-3-13-129244-5 , p. 110 ff.
- Otto Westphal , Theodor Wieland , Heinrich Huebschmann: life regulator. Of hormones, vitamins, ferments and other active ingredients. Societäts-Verlag, Frankfurt am Main 1941 (= Frankfurter Bücher. Research and Life. Volume 1), in particular pp. 9–35 ( History of hormone research ), here: pp. 12 f. ( The glands ).