Endoplasmic reticulum
- Pronunciation
- /en-doh-PLAZ-mik rih-TIK-yoo-lum/
- Category
- Physiology
- Singular
- endoplasmic reticulum
- Plural
- endoplasmic reticula
Definition
An interconnected network of -enclosed cisternae and tubules within the of eukaryotic , continuous with the nuclear envelope, that functions in protein synthesis, folding, modification, lipid synthesis, and calcium storage. The rough endoplasmic reticulum (RER) is studded with and specializes in protein synthesis and processing; the smooth endoplasmic reticulum (SER) lacks ribosomes and is involved in lipid metabolism, detoxification, and calcium regulation. In , the ER is particularly prominent in secretory cells such as those producing silk proteins in larval , venom components in arachnid cheliceral glands, and synthase for formation during cycles.
Etymology
From Greek endo- (within) + plasm (molded substance, ) + Latin reticulum (small net), referring to its net-like distribution throughout the cytoplasm
Example
In the silk glands of Bombyx mori larvae, extensive rough endoplasmic reticulum produces and processes the fibroin and sericin proteins that constitute silk; during the fifth instar, RER cisternae proliferate dramatically to meet the massive secretory demand before cocoon spinning.
Synonyms
- ER
Related Terms
- Ribosome
- golgi apparatus
- cisterna
- protein folding
- secretory cell
- chitin synthase
- Molting hormone
- ecdysteroid synthesis
Usage Notes
The distinction between RER and SER is functional and morphological rather than strictly compartmentalized—the two forms are continuous and interconvertible depending on activity. In histology, 'ergastoplasm' (an older term for prominent RER) is occasionally encountered in descriptions of secretory tissues. The ER is absent from mature mammalian erythrocytes but present in all arthropod cell types; claims of absence in spermatozoa refer to certain mammalian sperm, not arthropod sperm, which retain ER-derived structures. When describing arthropod ultrastructure, specify RER versus SER based on presence and functional context rather than appearance alone.