Excretory Processes

EXCRETORY PROCESSES. Based on the nature of the substances released by cells, one should distinguish between the processes of secretion (see) and excretion (see), although it is impossible to establish a sharp morphological difference between them. The release of substances from cells cannot always be detected in the form of clear morphological changes in cellular structure, and, undoubtedly, a large quantity of substances released by cells escapes morphological analysis. Nevertheless, especially thanks to the use of dyes for the study of excretory processes, it is already possible to form a more or less clear idea of the main stages of the phenomenon being studied, at least from a morphological point of view. The formation of substances subject to release, as can be judged from some cases, occurs, apparently, with the undoubted participation of the cell nucleus, and in many cases, one can observe the depletion of excretory cells of nuclear chromatin and its exit into the cell body in the form of so-called chromidia (see). Recently, many authors have linked the production of secretions (excretions) with the activity of the cellular chondriome or the intracellular reticular apparatus of Golgi (Nasonov). In cases where the released substances can be fixed for morphological study, either directly or by staining and impregnation, in the early stages of the process, one can see the formation of small proteinaceous granules in the cells, which either turn into the secretion (excretion) themselves or act as condensers for the compounds to be released. This is the case in the production of mucus by goblet cells, the formation of saliva gland secretion, and in the poisonous glands of some animals.

In the glands of some animals, in the pancreas [see separate table (Vol. V, col. 27-28), figs. 1-3], and in the interstitial cells of the gonads, these protein granules then undergo various changes: they dissolve into liquid droplets (goblet cells, salivary glands, lacrimal glands) or turn, for example, into lipoid granules (cells of the 'puberty gland'). In the basal part of many excretory cells, a rather coarse rod-like striation has been described, and in some cells (epithelium of the convoluted tubules of the kidneys), a special structure of the free surface (brush border—Burstenbesatz). Some authors (Chasovnikov, Gurvich) have noted that the initially formed granules or vacuoles move from the base of the cell to the surface and then exit into the lumen of the excretory duct. When certain dyes (indigo carmine, methylene blue, toluidine blue, etc.) are introduced into a complex organism, one can see that colored granules and vacuoles appear in the excretory cells; they are most often located in the region of the Golgi reticular apparatus. The expulsion of the formed substances from the cell can occur through the free surface by its rupture or with the help of special intracellular tubules, secretory capillaries (parietal cells of the stomach, serous glands). Sometimes a portion of the cell between the nucleus and the free surface is destroyed and sloughs off entirely, thereby forming a secretion (mammary gland). Often, substances exit the cell not in the form of definitive chemical compounds, but in the form of a proenzyme, and only later, along the further path, do they acquire their final properties under the influence of corresponding agents (e.g., zymogen of the pancreas, which transitions into an active state in the lumen of the intestine). The question of whether the released substances are a product of the specific activity of the protoplasm of the corresponding cells or are brought into them more or less ready-made cannot currently be considered finally resolved, since both the synthesis of such substances in the cell body and the selective absorption of ready-made substances by cells from the blood and lymph are equally probable.