The duties of the smooth endoplasmic reticulum vary depending on the type of cell, but one of the most important functions of this cellular structure is the synthesis of phospholipids and cholesterol. The smooth endoplasmic reticulum carries out these duties in a variety of cells, but plays more specific roles in specialized cells, such as liver cells. In liver cells, the smooth endoplasmic reticulum helps to purify and detoxify compounds that are produced through metabolic processes.
Smooth endoplasmic reticulum coexists with rough endoplasmic reticulum, which performs complementary yet vastly different roles. Together, the smooth and rough components form a larger cell structure called the endoplasmic reticulum. The endoplasmic reticulum, also referred to as ER, exists as a large and complex network in many types of cells. The rough and smooth compartments of the ER take the form of membranes, which can cover up to half of the surface area of their home cells. Smooth and rough endoplasmic reticula are located on the outermost portions of cells, and have porous, permeable surfaces that allow for the passage of certain substances. The smooth endoplasmic reticulum helps to coordinate and facilitate the passage of phospholipids along with proteins and enzymes, such as cytochrome P450, which helps breakdown carcinogens and organic molecules in liver cells.