The eukaryotic cell cytoplasm contains numerous pockets and tubes whose walls have an organization similar to that of the plasma membrane.
These membrane structures form a complex network of interconnected channels known as the endoplasmic reticulum. Two types of reticulum can be distinguished: rough (or granular) and smooth (or agranular).
Rough (RER) and smooth (REL) endoplasmic reticulum
O rough endoplasmic reticulum (RER), also called ergastoplasma, is formed by flat bags whose membranes have a warty appearance due to the presence of granules - the ribosomes - adhered to its outer surface (facing the cytosol).
Already the smooth endoplasmic reticulum (REL) It is formed by tubular membrane structures, without adhered ribosomes, and therefore with a smooth surface.
The two types of lattice are interconnected and the transition between them is gradual. If we look at the endoplasmic reticulum starting from the rough reticulum towards the smooth one, we see the pockets become smaller and the amount of adhered ribosomes progressively decrease until it ceases to exist.
Functions of the endoplasmic reticulum
The endoplasmic reticulum acts as a substance distribution network within the cell. In the liquid inside your bags and tubes, various types of substances move without mixing with cytosol.
An important function of smooth endoplasmic reticulum is the production of lipids. THE lecithin and cholesterol, for example, the major lipid components of all cell membranes are produced in REL. Other types of lipids produced in the smooth reticulum are steroid hormones, among which are the testosterone and the estrogen, sex hormones produced in the gonad cells of vertebrate animals.
The smooth endoplasmic reticulum also participates in the body's detoxification processes. In liver cells, REL absorbs toxic substances, modifying or destroying them, so as not to cause damage to the body. It is the action of the liver cell reticulum that allows to eliminate part of the alcohol, medicines and other potentially harmful substances we ingest.
Inside the smooth reticulum pockets there may also be substance storage. Plant cell vacuoles, for example, are reticulum-derived membrane pockets that grow by accumulating aqueous solutions stored therein.
The rough endoplasmic reticulum, thanks to the presence of ribosomes, is responsible for much of the cell's protein production. Proteins made in the RER ribosomes penetrate the pouches and move toward the Golgi apparatus, passing through the narrow, tortuous channels of the smooth endoplasmic reticulum.