In addition to organelles, cells contain cellular inclusions. They can be found not only in the cytoplasm, but also in some organelles, such as mitochondria and plastids.
What are cellular inclusions?
These are formations that are not permanent. Unlike organoids, they are not as stable. In addition, they have a much simpler structure and perform passive functions, such as a backup.
How are they built?
Most of them have a teardrop shape, but some may be different, for example, similar to a blot. As for the size, it may vary. Cellular inclusions can be either smaller than organelles, or the same 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 cellular inclusions are built from chemical compounds that entered the cell from the outside. Those that are formed from substances produced by the cell itself are called endogenous. Viral inclusions, although synthesized by the cell itself, however, this occurs as a result of the entry of virus DNA into it. The cell simply takes it for its DNA and synthesizes the virus protein from it.
Depending on the functions that cell inclusions perform, they are divided into pigment, secretory and trophic.
Next, inclusions are divided into types depending on the specific chemical compounds of which they are composed.
Cell inclusions: functions
They can have three functions. 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 emergencies. Contained in many cells of the body. |
| Pigmented | Formed from pigments - substances of bright color. They provide the cell with a certain color. Contained only in some 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 functions of the non-permanent formations in the cell.
Inclusions of animalscells
The cytoplasm of an animal contains both trophic and pigment inclusions. Some cells also have secretory cells.
Glycogen inclusions are trophic in animal cells. They have the shape of a granule with a size of about 70 nm.
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 glucose and glucogen metabolism: insulin and glucagon. They are both produced by the pancreas. Insulin is responsible for the formation of glycogen from glucose, while glucagon, on the contrary, is involved in the synthesis of glucose.
Most inclusions of glycogen are found in liver cells. They are also present in large quantities in the composition of muscles, including the heart. Glycogen inclusions of liver cells have 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, animal cells are characterized by lipid inclusions. These are also trophic inclusions, thanks to which the body can receive energy in an emergency. They are composed of fats and have a teardrop shape. 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 contain numerous small ones.
As for pigment inclusions, animal cells are characterized by thosewhich are made up of melanin. Thanks to this substance, the iris of the eye, skin and other parts of the body have a certain color. The more melanin inclusions in the cells, the darker what is made of these cells.
Another pigment that can be found in animal cells is lipofuscin. This substance is yellow-brown in color. It accumulates in the heart muscle and liver as organs age.
Plant cell inclusions
Cell inclusions, the structure and functions of which we are considering, are also found 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 in shape. Their size can 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 typical for animals. They are made up of simple proteins - proteins. Protein inclusions are of two types: aleurone grains and protein bodies. Aleurone grains may contain either crystals or simply amorphous protein. So, the former are called complex, and the latter are simple. Simple aleurone grains, which are composed of amorphous protein, are less common.
Regardingpigment inclusions, then plants are characterized by plastoglobules. They contain carotenoids. Such inclusions are typical for plastids.
Cellular inclusions, the structure and functions of which we are considering, mostly 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 the vacuoles of the cell. These crystals can come in a wide variety of shapes and are often unique to certain plant species.
