Are there different types of endoplasmic reticulum?

Yes, there are two types of endoplasmic reticulum – smooth endoplasmic reticulum and rough endoplasmic reticulum. They vary in terms of their structure as well as their functions. However, they are essentially two parts of the same organelle and work together to synthesize and transport molecules within the cell and outside the cell.  

Smooth Endoplasmic Reticulum

• The smooth or agranular endoplasmic reticulum is so named because of its smooth outer surface. This is due to the absence of ribosomes attached to its membranes.
• Its main functions include lipid synthesis, carbohydrate metabolism, and calcium homeostasis.
• Smooth ER occurs mostly in cells that are active in lipid metabolism. These include adipose cells, leucocytes, muscle cells, interstitial cells, glycogen storing cells of the liver, and retinal cells.

Rough Endoplasmic Reticulum

• The rough or granular endoplasmic reticulum is so named because of its rough outer surface. Its rough texture is due to the presence of ribosomes that remain attached to its membranes.
• Its main functions include protein synthesis, protein folding, and protein sorting. 
• Rough ER are found in abundance in cells dedicated to protein synthesis. These include plasma cells, liver cells, pancreatic cells, and goblet cells.