Cytoplasmic inclusions are primarily metabolic products that are stored in the cytoplasm, typically in long-lived cells such as hepatocytes, neurons, and cardiac muscle cells. Some examples of these include glycogen granules (a storage form of glucose seen as small, dark granules in the cytoplasm in TEM images), melanin pigment granules, lipid droplets, and residual bodies or lipofuscin granules. Some of these inclusions are visible in routinely prepared, H&E stained sections, and most are visible in electron micrographs.

Melanin pigment granules (arrows) are dark brown cytoplasmic inclusions that are visible in H&E stained specimens of skin. They function to protect epithelial cells (keratinocytes) of the epidermis from ultraviolet radiation.

Residual bodies or lipofuscin granules are another type of cytoplasmic inclusions. These granules represent materials remaining after lysosomal degradation. In routinely prepared, H&E stained specimens of liver, lipofuscin may be visible as light brown granules in the cytoplasm of hepatocytes.

Lastly, take a look at this specimen of a fatty liver, where lipid droplets are easily visualized as clear, circular spaces in the cytoplasm of hepatocytes. Remember that lipids are extracted during specimen preparation, resulting in empty spaces where lipid droplets were present.

Cytoskeletal structure comes next.