endoplasmic

Endoplasmic is a biological adjective derived from endo- (within) and plasma (cytoplasm). It is used mainly in reference to structures situated within the cytoplasm, most notably the endoplasmic reticulum (ER). The term also appears in discussions of endoplasm, the granular portion of the cytoplasm within cells, in contrast to the clearer ectoplasm described in early cytology.

The endoplasmic reticulum is a continuous membrane network that extends from the outer membrane of the nuclear envelope throughout the cytoplasm. It consists of flattened sacs (cisternae) and tubules. It is classed as rough or smooth, according to the presence of ribosomes on its surface as a rough ER.

Rough ER: Studded with ribosomes, rough ER synthesizes secreted and membrane proteins, translates polypeptides into the ER lumen or membrane, and assists in protein folding and quality control. It also initiates N-linked glycosylation of newly made proteins.

Smooth ER: Lacks ribosomes and is involved in lipid and phospholipid synthesis, metabolism of carbohydrates, detoxification of drugs and toxins (notably in liver cells), and calcium storage. It also participates in steroid hormone synthesis in certain tissues.

Together with the Golgi apparatus and vesicles, the ER forms the secretory pathway, delivering proteins and lipids to their destinations. In eukaryotic cells, the endoplasmic reticulum is a membrane-bound organelle contiguous with the nuclear envelope, and its proper function is essential for cellular homeostasis; dysfunction is implicated in diseases involving protein misfolding and lipid metabolism.