Endoplasmic reticulum



(cell biology) A membrane-bounded organelle that occurs as labyrinthine, interconnected flattened sacs or tubules connected to the nuclear membrane, running through the cytoplasm, and may well extend into the cell membrane


The endoplasmic reticulum (ER) is an organelle that occurs as interconnected network of flattened sacs or tubules (called cisternae). The membranes of the ER are connected to the nuclear membrane and run through the cytoplasm. They may also extend into the cell membrane. The ER is one of the three components of the GERL system, in which the Golgi apparatus and the lysosomes are the other components. It is found in different cell types. However, it is lacking in red blood cells and spermatozoa.

There are two kinds of ER: the RER, or the rough endoplasmic reticulum, and the SER, or the smooth endoplasmic reticulum. The RER bears many ribosomes on its outer surface giving it a rough appearance; hence, its name. Since RER has ribosomes attached to its surface it is therefore involved in protein synthesis and secretion. It synthesizes and secretes serum proteins (such as albumin) in the liver, and hormones (such as insulin) and other substances (such as milk) in the glands. The SER, on the other hand, does not have ribosomes on its surface. Its functions include synthesis of lipids, metabolism of carbohydrates and calcium concentration, drug detoxification, and attachment of receptors on cell membrane proteins. It is also involved in intracellular transport, such as the transport of the products of the RER to other cell parts like Golgi apparatus.

Word origin: from the Greek endon, meaning within, plasma, meaning anything formed or moulded, and Latin reticulum, meaning a small net

Abbreviation / Acronym: ER


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