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It is a type of organelle made up of two subunits – rough endoplasmic reticulum (RER), and smooth endoplasmic reticulum (SER). The endoplasmic reticulum is found in most eukaryotic cells and forms an interconnected network of flattened, membrane-enclosed sacs known as cisternae (in the RER), and tubular structures in the SER.
Synthesis of proteins is by the rough endoplasmic reticulum (RER), and both the rough and smooth endoplasmic reticulum (SER) are involved in secretion of the proteins formed. [citation needed] The endoplasmic reticulum (ER) is involved in conjugation of proteins to lipid and carbohydrate moieties synthesized by, or modified within, the hepatocytes.
The ER has two forms: the rough ER, which has ribosomes on its surface that secrete proteins into the ER, and the smooth ER, which lacks ribosomes. [2] The smooth ER plays a role in calcium sequestration and release and also helps in synthesis of lipid.
Enzymes of the smooth ER are vital to the synthesis of lipids, including oils, phospholipids, and steroids. Sex hormones of vertebrates and the steroid hormones secreted by the adrenal glands are among the steroids produced by the smooth ER in animal cells. The cells that synthesize these hormones are rich in smooth ER. [24] [27]
Endoplasmic reticulum: outer part of the nuclear envelope forming a continuous channel used for transportation; consists of the rough endoplasmic reticulum and the smooth endoplasmic reticulum Rough endoplasmic reticulum (RER): considered "rough" due to the ribosomes attached to the channeling; made up of cisternae that allow for protein production
Smooth endoplasmic reticulum makes hormones and lipids, degrades toxins, and controls cellular levels of calcium. Though most control of cell division is present in the nucleus, the centrosomes present in the endoplasm assist with spindle formation. The endoplasm is the site of many activities necessary for the cell to maintain homeostasis. [2]
The unusual microscopic anatomy of a muscle cell gave rise to its terminology. The cytoplasm in a muscle cell is termed the sarcoplasm; the smooth endoplasmic reticulum of a muscle cell is termed the sarcoplasmic reticulum; and the cell membrane in a muscle cell is termed the sarcolemma. [9]
The microsomal ethanol oxidizing system (MEOS) is an alternate pathway of ethanol metabolism that occurs in the smooth endoplasmic reticulum in the oxidation of ethanol to acetaldehyde. While playing only a minor role in ethanol metabolism in average individuals, MEOS activity increases after chronic alcohol consumption.