1. Smooth endoplasmic reticulum-SER: The endoplasmic reticulum that does not have ribosomes is called smooth endoplasmic reticulum or SER. It synthesizes lipids. It releases calcium during muscle contraction. Smooth endoplasmic reticulum is abundant in adipose cells, testes, adrenal cortex cells, muscle cells and liver cells.
2. Rough endoplasmic reticulum-RER: The endoplasmic reticulum that has ribosomes is called rough endoplasmic reticulum or RER. It synthesizes proteins. It stores calcium during muscle contraction. Rough endoplasmic reticulum contains tiny glyoxysome particles. These tiny glyoxysome particles are called microsomes. Pancreatic cells, liver cells, plasma cells and goblet cells have rough endoplasmic reticulum.