Cytoplasmic inclusions

cytoplasmic inclusions are substances of cytoplasm that are considered to be non-living. These substances are characterized by two characteristics which are,
1. No metabolic activity
2.  Not bounded by a membrane

These substances mean cytoplasm inclusions are classified into three groups which are,

1. Stored food material
2.  Pigment
3.  Crystal



1.Stored food material

Cytoplasmic inclusions mainly present in the form of stored food material are lipids and glycogen.

I. Lipids

Lipids are mainly present in the fat cells but they are also present in other cells in the form of a spherical fat droplet.  These droplets are not bounded by a membrane. The type of lipids mainly presents in the cells are triglycerides.  Triglycerides are used when the cell needs energy.  When the tissue is prepared for light microscopy the lipid is dissolved out and is represented by empty spaces in the cytoplasm.

II. Glycogen

Glucose is mainly stored in the form of glycogen in the cells. Glycogen is abundant in liver cells and striated muscle cells. During the preparation of tissue for light microscopy, glycogen is usually lost and is represented by empty regions in the cytoplasm.

2. Pigments

Pigments are colored substances present in the cytoplasm that do not requires dyes. Pigments which are mainly found in the human cells are lipofuscin, Melanin, and crystals.

I. Lipofuscins

This pigment represents deposits of indigestible substances. The amount of this pigment increases with age. This pigment is also abundant in cells that are long-living such as cardiac cells.  This pigment indicates the wear and tear of the cell.

II. Melanin

Melanin is mainly found in the cells known as melanocytes that are mainly found in the basal layer of the epidermis of the skin. Melanin granules are formed in the melanocytes that are then transferred into the keratinocytes of the epidermis. These granules present in the epidermis protects the cells against the harmful effect of solar ultraviolet radiation.

3.Crystals(cytoplasmic inclusions)

Cytoplasmic inclusions in some cells also contain crystal or crystal-like structures in their cytoplasm. These cytoplasmic inclusions are proteins in nature but their importance is not well understood. Cells of the human body in which crystals are present are Sertoli cells and Leydig cells of the testis. Occasionally crystal is found to be present in macrophages cytoplasm.