The ability of living beings to maintain a constant internal environment is called homeostasis. Changes in external environment do not have much impact on the internal environment as the living beings have a self-regulated system. The endoplasmic reticulum (ER) is a critical site of protein, lipid, and glucose metabolism, lipoprotein secretion, and calcium homeostasis.The ER provides significant adaptive capacity to metabolism in managing the periodic cycles associated with feeding, fasting and other metabolic demands of limited duration.