External Secretion

EXTERNAL SECRETION, the process of production and secretion by glands of various juices which are released either externally (milk glands) or into the digestive tract through special ducts. Glands transform substances brought by the blood into specific products (saliva, gastric juice, bile, etc.). Ludwig, using the example of saliva, showed that the process of E. s. is not simple filtration, since the pressure of the separated saliva can be greater than the blood pressure in the corresponding artery. E. s. is a special activity of the cells of the glandular epithelium. Working cells of the gland differ morphologically from non-working ones by greater or lesser granularity, due to the presence of zymogen granules (Heidenhain). During the work of the gland, blood vessels dilate and lymph formation increases, but there is no direct connection between the filling of the gland's blood vessels and its external secretion, since secretion can also occur with narrowed vessels. The secretion process is related to the balance of alkaline and acidic components of the blood. Starling and Bayliss showed that with repeated administration of secretin, the pancreas stops secreting juice, but if soda is introduced into the blood, secretin begins to act again. External secretion is contrasted with internal secretion, in which substances produced by the gland are released not into the external environment, but into the internal environment of the body (lymph and blood). Claude Bernard, using the example of the liver, showed that the latter not only produces bile flowing into the duodenum, but also maintains the sugar level in the blood at a certain level by releasing sugar into the hepatic veins. Indeed, through precise analyses, one can establish the difference in sugar content in the blood of the portal and hepatic veins during and outside of digestion. E. s. differs from excretion (see) in that in E. s., specific products are formed in the gland itself as a result of the chemical process of the gland cell, while in excretion, ready-made products are expelled to the outside without undergoing changes in the gland itself. Excretory organs are the kidneys and sweat glands.