In addition to organelles, cell inclusions are present in the cells. They can be found not only in the cytoplasm, but also in some organoids, such as mitochondria and plastids.
What are cell inclusions?
These are formations that are not permanent. Unlike organelles, they are not so stable. In addition, they have a much simpler structure and perform passive functions, such as, for example, backup.
How are they built?
Most of them have a droplet shape, but some may be others, for example, similar to a blot. As for the size, it can vary. Cellular inclusions can be either smaller organoids, or the same in size or even larger.
They consist mainly of one specific substance, in most cases organic. It can be either fat, or carbohydrate or protein.
Classification
Depending on where the substance from which they are composed comes from, there are the following types of cellular inclusions:
- exogenous;
- endogenous;
- viral.
Exogenous cell inclusions are built from chemical compounds that enter the cell from the outside. Those that are formed from substances produced by the cell itself are called endogenous. Although viral inclusions are synthesized by the cell itself, however, this occurs as a result of the ingress of the DNA of the virus. A cell simply takes it for its DNA and synthesizes a virus protein from it.
Depending on the functions that cell inclusions perform, they are divided into pigment, secretory and trophic.
Further inclusions are divided into species depending on the specific chemical compounds of which they consist.
Cellular inclusions: functions
They can have three functions. Let's consider them in the table.
| Cell inclusions | Functions |
| Trophic | Reserve. In the form of such inclusions, the body stores nutrients. Their cell can be used in emergency cases. Contained in many cells of the body. |
| Pigmented | Formed from pigments - bright colored substances. They provide the cell with a specific color. Contained only in certain cells of the body. |
| Secretory | They are built from enzymes. They are present only in specialized cells. For example, in the cells of the pancreas. |
These are all the functions of intermittent formations in the cell.
Inclusion of animal cells
The animal’s cytoplasm contains both trophic and pigment inclusions. In some cells, secretory cells are also present.
Trophic in animal cells are glycogen inclusions . They have a granular shape about 70 nm in size.
Glycogen is the main reserve substance of the animal. In the form of this substance, the body stores glucose. There are two hormones that regulate the metabolism of glucose and glucogen: insulin and glucagon. They are both produced by the pancreas. Insulin is responsible for the formation of glycogen from glucose, and glucagon, on the contrary, is involved in the synthesis of glucose.
Most glycogen inclusions are found in liver cells. They are also present in large numbers in the composition of the muscles, including the heart. Glycogen inclusions of liver cells are in the form of granules about 70 nm in size. They gather in small clusters. Glycogen inclusions of myocytes (muscle cells) have a rounded shape. They are single, slightly larger than ribosomes.
Also, lipid inclusions are characteristic of animal cells. These are also trophic inclusions, thanks to which the body can receive energy in an emergency. They are made up of fats and are drop-shaped. Basically, such inclusions are contained in the cells of adipose connective tissue - lipocytes. There are two types of adipose tissue: white and brown. White lipocytes contain one large drop of fat, brown cells - numerous small ones.
As for pigment inclusions, those that are composed of melanin are characteristic of animal cells. Thanks to this substance, the iris, skin and other parts of the body have a certain color. The more melanin inclusions in the cells, the darker what is composed of these cells.
Another pigment that can be found in animal cells is lipofuscin. This substance is yellow-brown. It accumulates in the heart muscle and liver as organs age.
Plant cell inclusions
Cellular inclusions, the structure and functions of which we are considering, are also contained in plant cells.
The main trophic inclusions in these organisms are starch grains . In their form, plants store glucose. Typically, starch inclusions are lenticular, spherical or ovoid. Their size may vary depending on the type of plant and on the organ in whose cells they are contained. It can be from 2 to 100 microns.
Lipid inclusions are also characteristic of plant cells. They are the second most common trophic inclusions. They have a spherical shape and a thin membrane. They are sometimes called spherosomes.
Protein inclusions are present only in plant cells, they are not characteristic of animals. They consist of simple proteins - proteins. Protein inclusions are of two types: aleurone grains and protein bodies. Aleuron grains can contain either crystals or just an amorphous protein. So, the former are called complex, while the latter are called simple. Simple aleuron grains, which are composed of amorphous protein, are less common.
As for pigment inclusions, plastoglobules are characteristic of plants . They accumulate carotenoids. Such inclusions are characteristic of plastids.
The cell inclusions, the structure and functions of which we are considering, for the most part consist of organic chemical compounds, but in plant cells there are also those that are formed from inorganic substances. These are calcium oxalate crystals.
They are present only in cell vacuoles. These crystals can be of the most diverse form, and often it is individual for certain types of plants.