The smooth endoplasmic reticulum (ER) is a network of tubules in plant and animal cells that is involved in lipid synthesis and metabolism. Discovered in 1945 in Belgium, smooth ER lacks ribosomes on its surface and has a diameter of about 150 nanometers. Its main functions include steroid hormone production, detoxification of organic compounds, glucose release in liver cells, and calcium ion regulation. If smooth ER stops working properly, lipid production and metabolism would be disrupted, affecting the entire organism.