Cellular Inclusions: General Characteristics
- Cellular inclusions are cytoplasmic deposits or lumps within the cytoplasm.
- They are generally transitory components.
- Unlike organelles, inclusions are not metabolically active and are not enclosed by a membrane.
- They serve primarily as storage sites.
Composition and Examples
Cellular inclusions are typically deposits of:
- Carbohydrates:
Glycogen granules are electron-dense particles that can be individual or clustered. They are a ready source of energy and are abundant in cells with high metabolic activity, such as liver cells.
- Lipids:
Fat droplets (lipid droplets) are prominent in cells like adipocytes (fat cells), adrenal cortex cells, and liver cells. They appear as small spherical structures with homogeneous matrices and are enclosed by a single monolayer of phospholipids with peripheral proteins. In routine tissue processing for paraffin sections, fat droplets are often removed, leaving empty spaces in the cells.
- Pigments:
Pigment deposits include various complex substances such as lipofuscin and melanin.
Lipofuscin granules are an accumulating by-product of lysosomal digestion in long-lived cells. These are residual bodies left from lysosomal digestion.
Melanin granules serve to protect cell nuclei from DNA damage caused by light.
Hemosiderin granules, which contain the protein ferritin (a storage complex for iron), are very electron-dense and appear brownish with a light microscope.