cytoplasm
Meaning of cytoplasm: If the nucleus is the archive, this is the factory floor, and pathologists read the two compartments against each other as a ratio.
Definition of cytoplasm
Cytoplasm is everything inside a cell between the outer membrane and the nucleus. It is made of cytosol, a watery gel of salts, sugars and proteins, and the organelles suspended in it, held in shape by a scaffold of protein filaments. Most of the cell's chemical work, including energy production and protein assembly, happens there.
What is in it?
| Component | What it contributes |
|---|---|
| Cytosol | The fluid itself, where many chemical reactions take place |
| Mitochondria | Convert nutrients into the energy currency the cell spends |
| Ribosomes | Read messenger RNA and build proteins from it |
| Endoplasmic reticulum | Folds and processes proteins; a smooth form makes lipids |
| Golgi apparatus | Sorts, labels and packages proteins for delivery |
| Lysosomes | Digest worn-out components and imported material |
| Cytoskeleton | Maintains shape, moves cargo and pulls the cell apart when it divides |
The compartment is bounded on the outside by the plasma membrane and on the inside by the envelope of the nucleus, and material crosses both boundaries under control rather than freely.
What happens there?
Glucose is broken down in the cytosol in the first stage of energy release, and the products are handed to the mitochondria for the rest. Protein synthesis takes place on ribosomes, some floating free and some studding the endoplasmic reticulum, and newly made chains are folded, checked and shipped onward. Fats and steroids are assembled in the smooth reticulum, waste is dismantled in lysosomes, and signals arriving at the surface are relayed inward through chains of cytoplasmic proteins. The cytoskeleton runs transport along its filaments like rails, so the interior is organized rather than a soup, and those filaments also drive the movement of cells that migrate.
Why do pathologists describe it?
Because the cytoplasm carries clues the nucleus does not. Its volume relative to the nucleus is the nuclear-to-cytoplasmic ratio, and a shift toward a large nucleus in a thin rim of cytoplasm is a common feature of cancer cells. The color it takes with routine stains, described as eosinophilic when pink and basophilic when blue, indicates what the cell is making. Clear cytoplasm suggests stored glycogen or fat and characterizes certain tumors. Granules, mucin droplets, pigment or viral inclusions each point toward a particular diagnosis, and stains that mark specific cytoplasmic proteins are used to establish which tissue a cancer came from.
Used in a sentence
The pathologist described abnormal cytoplasmic features in several of the examined cells.
Good to know
Pathologic evaluation of a cell considers the appearance of both the cytoplasm and the nucleus, since abnormalities can appear in either compartment independently or together.
Word origin
Where “cytoplasm” comes from
Formed from cyto-, from Greek kytos, meaning cell, and plasm, from Greek plasma, meaning something formed or molded.