# Endoplasmic Reticulum --- The **endoplasmic reticulum**, or just the **ER** is a part of the [[endomembrane system]] that builds and processes proteins and fats. It is one big membrane continuous with the [[nucleus|nuclear envelope]], and it's divided into two distinct regions, the rough and the smooth ER. ![[endomembrane system.png]] **The rough ER** is formed of a network of flattened sacs and tubules. There are many [[ribosome|ribosomes]] studded into the surface of the rough ER, and they spluush out their proteins into the "lumen", or interior of the ER. This is totally devoted to building [[translation|proteins]] that are either going to end up as a [[membrane proteins|membrane protein]] or is going to be secreted. The **smooth ER** is the site of a lot of [[fatty acids]] and [[phospholipid]], [[lipids]] and [[sterol|steroid]] synthesis. Some cells that produce particular products have a lot extra smooth ER, such as [[sebaceous glands]], and some [[endocrine gland|endocrine glands]] (I think, anyway). In the [[liver]] the smooth ER process lipid and cholesterol metabolism, and is the site for the detoxification of many drugs, pesticides and carcinogens. In the [[intestines|intestinal cells]] the smooth ER helps the absorption, syntheses and transportation of [[lipids|fats]] In the [[skeletal muscle]] and [[cardiac muscle]] it's important for the storage and release of calcium. ___