The components of the endomembrane system are the
rough endoplasmic reticulum,
the golgi apparatus,
various transport vesicle,
and storage vesicles in the cytoplasm of the cell.
The rough endoplasmic reticulum (also known as the microsome fraction) is involved in the synthesis of certain proteins. Not all cellular proteins are synthesized on the RER. The proteins that are synthesized on the RER are, in general, those that will be secreted, be sent to the lysosome or other intracellular organelles that are a part of the endomembrane system, or become part of the plasma membrane (integral membrane proteins.
The proteins synthesized on the RER are carried to the Golgi apparatus by transport vesicles. In the Golgi apparatus the proteins are sorted and modified.
The animation below shows the flow of proteins through the endomembrane system