Smooth muscle tissue: features of the structure. Properties of smooth muscle tissue

Animal tissues perform a very important function in the organisms of living beings - they form and lining all organs and their systems. Of particular importance among them is muscular, since its importance in the formation of the external and internal cavity of all structural parts of the body is a priority. In this article we will consider what is a smooth muscle tissue, the features of its structure, properties.

Varieties of these tissues

In the animal body there are few types of muscles:

• Striated crosswise;
• Smooth muscle tissue.

Both of them have their own characteristic features of structure, the functions performed and the properties that are manifested. In addition, they are easy to distinguish between themselves. After all, both have their own unique pattern, formed due to the constituent cells of the protein components.

The strip strips are also divided into two main types:

• Skeletal;
• Heart.

The name itself reflects the main areas of location in the body. Its functions are extremely important, because it is this musculature that provides for the reduction of the heart, the movement of the limbs and all other moving parts of the body. However, smooth muscle is no less significant. In what its features consist, we will consider further.

In general, it can be seen that only the well-coordinated work performed by smooth and striated muscle tissue allows the whole body to function successfully. Therefore, it is impossible to determine a more or less significant of them.

Smooth muscle tissue: features of the structure

The main unusual features of the structure under consideration are the structure and composition of its cells - myocytes. Like any other, this tissue is formed by a group of cells, similar in structure, properties, composition and functions performed. General features of the structure can be identified in several paragraphs.

1. Each cell is surrounded by a dense plexus of connective tissue fibers, which looks like a capsule.
2. Each structural unit is closely adjacent to the other, the intercellular spaces are practically absent. This allows the entire fabric to be tightly packed, structured and durable.
3. Unlike the striated colleague, this structure can include differently shaped cells in its composition.

This, of course, is not all of the characteristics that smooth muscle tissue has. The features of the structure, as already stated, are contained in the myocytes themselves, their functioning and composition. Therefore, below this question will be considered in more detail.

Smooth muscle musculature

Myocytes have different shapes. Depending on the localization in this or that organ, they can be:

• Oval;
• Spindle-shaped elongated;
• Rounded;
• Process.

However, in any case, their overall composition is similar. They contain such organelles as:

• Well-defined and functioning mitochondria;
• The Golgi complex;
• Core, more often elongated in shape;
• Endoplasmic reticulum;
• Lysosomes.

Naturally, the cytoplasm with normal inclusions is also present. It is interesting to note that smooth muscle musculature outside is covered not only by the plasmolemma, but also by the membrane (basal). This provides them with an additional opportunity for contact with each other.

These areas of contact are the features of smooth muscle tissue. Contact places are called nexus. It is through them, as well as through the pores that are present in these areas in the membrane, that impulses are transmitted between the cells, the exchange of information, water molecules and other compounds.

There is one more unusual feature, which has a smooth muscle tissue. The peculiarities of the structure of its myocytes are that not all of them have nerve endings. Therefore, the Nexus are so important. To ensure that no cell is left without innervation, and the impulse could be transmitted through the adjacent structure through the tissue.

There are two main types of myocytes.

1. Secretory. Their main function is the production and accumulation of glycogen granules, the preservation of many mitochondria, polysomes and ribosomal units. The name of these structures is due to the proteins contained in them. These are actin filaments and contractile fibrin strands. These cells are most often localized around the periphery of the tissue.
2. Smooth muscle fibers. They have the form of spindle-shaped elongated structures containing an oval nucleus displaced toward the middle of the cell. Another name is leiomyocytes. They differ in that they have larger dimensions. Some particles of the mother organ reach 500 μm! This is a significant enough figure against all other cells in the body, more than an egg.

The function of smooth myocytes is also that they synthesize the following compounds:

• Glycoproteins;
• Procollagen;
• Elastans;
• Intercellular substance;
• Proteoglycans.

Joint interaction and well-coordinated work of the designated types of myocytes, as well as their organization, ensure the structure of smooth muscle tissue.

The origin of this musculature

The source of formation of this type of muscles in the body is not one. Three main variants of origin are distinguished. It is this that explains the differences that the structure of smooth muscle tissue has.

1. Mesenchymal origin. This has most of the smooth fibers. It is from the mesenchyme that virtually all tissues lining the inside of the hollow organs are formed.
2. Epidermal origin. The name itself says about localization - it's all the skin glands and their ducts. They are formed by smooth fibers that have such an appearance. Sweat, saliva, milk, tear-all these glands secrete their secret, due to irritation of myoepithelial cells - structural particles of the organ under consideration.
3. Neural origin. Such fibers are localized in one specific place - this is the iris, one of the shells of the eye. The contraction or dilatation of the pupil is innervated and controlled by these cells of smooth musculature.

Despite the different origins, the internal composition and the properties of all types of cells in the tissue in question remain approximately the same.

The main properties of this fabric

The properties of smooth muscle tissue correspond to those of the striated muscle. In this they are one. It:

• Conductivity;
• excitability;
• lability;
• Contractility.

In this case, there is one rather specific feature. If the striated skeletal musculature is able to rapidly contract (this is well illustrated by a tremor in the human body), the smooth one can be held in a compressed state for a long time. In addition, her activities are not subject to the will and mind of a person. Because it innervates its autonomic nervous system.

A very important property is the ability for prolonged slow stretching (contraction) and the same relaxation. So, this is the work of the bladder. Under the action of a biological fluid (by its filling) it is able to stretch, and then contract. Its walls are lined with smooth muscles.

Cell Proteins

Myocytes of the tissue in question contain many different compounds. However, the most important of them, ensuring the performance of the functions of contraction and relaxation, are precisely the protein molecules. They contain:

• Myosin filaments;
• Actin;
• Nebuline;
• Connectin;
• Tropomyosin.

These components are usually located in the cytoplasm of cells isolated from each other without forming clusters. However, in some organs, animals form bundles or strands called myofibrils.

The arrangement in the tissue of these bundles is mainly longitudinal. Moreover, both myosin fibers and actin fibers. As a result, a whole network is formed in which the ends of some are intertwined with the edges of other protein molecules. This is important for the rapid and proper reduction of the entire tissue.

The reduction itself occurs as follows: in the internal environment of the cell there are pinocytosis vesicles, in which calcium ions are necessarily contained. When a nerve impulse arrives, suggesting the need for contraction, this vial approaches the fibril. As a result, the calcium ion irritates the actin and it moves deeper between the threads of the myosin. This leads to the plasmalemma, and as a result, the myocyte is reduced.

Smooth muscle tissue: pattern

If we talk about striated tissue, then it is easy to recognize by striation. But that's what concerns the structure we are considering, this does not happen. Why is a smooth muscle tissue pattern different than its neighbor? This is due to the presence and location of protein components in the myocytes. In the smooth muscle structure, the threads of myofibrils of different nature are localized chaotically, without a definite ordered state.

That is why the fabric pattern is simply missing. In the stranded strand of actin is successively replaced by a transverse myosin. As a result, there is a picture - striation, through which the fabric and got its name.

Under the microscope, the smooth tissue looks very even and ordered, due to the longitudinally extending elongated myocytes densely adjacent to each other.

Areas of spatial location in the body

Smooth muscle tissue forms a fairly large number of important internal organs in the animal body. So, she was educated:

• intestines;
• Genital organs;
• Blood vessels of all types;
• Glands;
• Organs of excretory system;
• Airways;
• Parts of the visual analyzer;
• Organs of the digestive system.

Obviously, the localization of the tissue in question is extremely diverse and important. In addition, it should be noted that these muscles form mainly those organs that are subject to automatic control.

Ways to restore

Smooth muscle tissue forms important enough structures that have the ability to regenerate. Therefore, it is characterized by two main ways of recovery for injuries of various kinds.

1. Mitotic division of myocytes before formation of the necessary amount of tissue. The most common simple and quick way to regenerate. This is how the internal part of any organ, formed by smooth muscles, restores.
2. Myofibroblasts are able to transform into smooth tissue myocytes as needed. This is a more complex and rarely encountered way of regenerating this tissue.

Innervation of smooth muscles

Smooth muscle tissue performs its functions independently of the desire or unwillingness of a living being. This is due to the fact that its innervation is provided by the autonomic nervous system, as well as the processes of the nerves of the ganglia (spinal).

An example of this and the evidence can serve as a reduction or increase in the size of the stomach, liver, spleen, stretching and contraction of the bladder.

Functions of smooth muscle tissue

What is the significance of this structure? Why do you need smooth muscle tissue? Its functions are as follows:

• Prolonged contraction of the walls of organs;
• Development of secrets;
• Ability to respond to irritations and effects of excitability.