The Endomembrane system is a membranous component of the eukaryotic cell. The cytoplasm of the cell contains a system of membranous organelles that are suspended in it. The organelles are termed as a system even though they have different structures and functions as they are essential to the working of the cell. All these organelles work in coordination and they include the cell membrane, vacuoles, the nuclear membrane, lysosomes, Golgi complex, vesicles and the endoplasmic reticulum (ER). Endoplasmic reticulum represents a network of tiny tubular structures scattered in the cytoplasm. It divides the cytoplasm into two distinct compartments – luminal (inside ER) and extra luminal (outside ER). ER is present in the cytoplasm in two forms – Rough ER (embedded with ribosomes) and Smooth ER (free from ribosomes). Rough ER helps in synthesis and secretion of proteins whereas Smooth ER synthesizes lipids. Endoplasmic reticulum transpires in two forms: a type with ribosome-studded surface and another with a smooth surface. The latter is called the smooth endoplasmic reticulum, and the former is called the rough endoplasmic reticulum. These membranes form continuous folds, eventually joining the outer layer of the nuclear membrane. Except for sperm cells and red blood cells, the endoplasmic reticulum is observed in every other type of eukaryotic cell. Rough endoplasmic reticulum has ribosomes embedded within its structure, giving a “rough” appearance. Smooth endoplasmic reticulum does not have these ribosomes; hence appear “smooth.” Structure of Endoplasmic Reticulum The structure of endoplasmic reticulum is shaped like a sac. Since ER is of two types, each has its own distinguishing features: Rough Endoplasmic Reticulum The rough endoplasmic reticulum is named so because of its appearance. It is a series of connected flattened sacs having several ribosomes on its outer surface, hence the name. It synthesizes and secretes proteins in the liver, hormones and other substances in the glands. Rough ER is prominent in cells where protein synthesis happens (such as hepatocytes) Smooth Endoplasmic Reticulum The smooth endoplasmic reticulum, on the other hand, does not have ribosomes. The smooth endoplasmic reticulum has a tubular form. It participates in the production of phospholipids, the chief lipids in cell membranes and are essential in the process of metabolism. Smooth ER transports the products of the rough ER to other cellular organelles, especially the Golgi apparatus. Function As stated above, the endoplasmic reticulum is categorised into two types, and both these types of ER perform specific functions: SER Function: Smooth ER is responsible for the synthesis of essential lipids such as phospholipids and cholesterol. Smooth ER is also responsible for the production and secretion of steroid hormones. It is also responsible for the metabolism of carbohydrates. The smooth ER stores and releases calcium ions. These are quite important for the nervous system and muscular system. RER Function: The majority of the functions of rough ER is associated with protein synthesis. Rough endoplasmic reticulum also plays a vital role in protein folding. Also ensures quality control (regarding correct protein folding). The second most important function after protein synthesis and protein folding is protein sorting. Submit Your Manuscript at https://www.imedpub.com/submissions/anatomical-science-research.html or anatomicalsci@scholarlymed.com Best Regards Jacqueline Managing Editor Journal of Anatomical Science and Research