And that's exactly why we call it the rough Er, because it contains those ribosomes inside the membrane of the Er. Now, what exactly is the function, the purpose of our Er? So basically the Er, the rough endoplasmic reticulum, functions to synthesize our proteins. It synthesizes proteins that end up either being secreted from the cell or end up in the cell membrane of our cell. So basically, we see that the nuclear envelope and the membrane of our Er are jointed. They're connected in these regions.