Some ribosomes produce integral proteins of cell membranes, secretory proteins, and proteins of lysosomes and various granules. These ribosomes are functioning on the cytoplasmic surface of endoplasmic reticulum cisterns. The reticulum subcompartment is called rough endoplasmic reticulum #1, #2. However, the ribosomal lining #1, #2, #3, #4 of the RER is not solid. The synthesis of new protein polypeptide chains for RER is initiated in the cytosol. Thus, ribosomes anchor the cytoplasmic surface of RER cisterns due to certain proteins (docking proteins). The synthesis then continues, and the polypeptide chain enters a cistern cavity via a channel (translocon) in the RER membrane. Cells of vascular walls (endothelial cells, pericytes), as well as other cells of the body, produce proteins of their own membranes and, in addition, other proteins to secrete them into the extracellular space. However, the production output is not large there, so the RER is usually poorly developed. Solitary RER cisterns which are distributed in the cytoplasm, and free polysomes #1, #2 meet the existing needs. If cells become activated, e.g. in case of neovascularization, the endothelium may get a secretory appearance. The image depicts the area of a gap junction between an endothelial cell and a pericyte. The capillary lumen contains a red blood cell