interior of ER Golgi is topologically equivalent to exterior of the cell

 

This exterior.......is it extracellular fluid? Interior of ER is Lumen?

The exterior of a cell is bathed in extracellular or tissue fluid. The interior of the endoplasmic reticulum and the Golgi apparatus is also referred to as the lumen. The topologic relationship is clear if one follows the contents and the inner leaflet of the ER traveling via vesicles to the Golgi, and then from the Golgi to the surface of the cell for exocytosis. Exocytosis puts the inner leaflet of the exocytic vesicle on the outside of the cell and the contents into extracellular space. Similarly, endocytosis makes intracellular vesicles that have the outer leaflet of the cell membrane as the inner leaflet of the vesicle. SM