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Phagocytosis - what is it? What is the essence of phagocytosis? Phagocytosis stages

So, phagocytosis - what is it? Let's try to understand the definition of this term. The word "phagocytosis" originated from two Greek morphemes - phagos (devouring) and kytos (cage). The international medical term phagokytosis, unlike russified, has the ending osis, which is translated from Greek as a "process" or "phenomenon." Thus, literally this definition means the process of recognition of a foreign agent by specific cells, a targeted movement towards it, capture and absorption and subsequent splitting. In this article we will talk about what the essence of phagocytosis is. Also we will talk about what kind of phagocytes are, consider the stages and find the difference between completed and unfinished phagocytosis.

The history of the discovery of special mobile cells

Outstanding Russian naturalist - II Mechnikov in 1882 - 1883 gg. Conducted experiments on intracellular digestion, studying the transparent larvae of sea stars. The scientist wondered if the multicellular organisms had the ability to seize food by separate cells. And also digest it as the simplest single-celled ones, for example amoebae do. II Mechnikov conducted the experiment: he injected carmine powder into the bodies of the larvae and watched the wall of cells grow around these small blood-red grains. They grabbed and swallowed the paint. Then the scientist had a hypothesis that in any organism there should be special protective cells that can absorb and digest other particles that harm the body. To confirm his hypothesis, the scientist used pink thorns, which introduced into the body the larvae of the starfish. Some time later, the scientist saw that the cells surrounded the thorns, trying to counteract the "pests" and push them out. These specific protective particles found in the body of the larva, the scientist called phagocytes. Thanks to this experience, II Mechnikov revealed phagocytosis. In 1883, he reported on his discovery at the Seventh Congress of Russian naturalists. Later, the scientist continued to work in this direction, created a comparative pathology of inflammation, as well as a phagocytic theory of immunity. In 1908, together with the scientist P. Ehrlich, he received the Nobel Prize for his most important biological research.

The phenomenon of phagocytosis - what is it?

II Mechnikov traced and clarified the role of phagocytosis in the protective reactions of the human body and higher animals. The scientist has established that this process plays a significant role in the healing of various wounds. The biological encyclopedic dictionary gives the following definition. Phagocytosis is an active capture, as well as the absorption of foreign objects, such as bacteria, microfungi and cell fragments, unicellular organisms or specific cells (phagocytes) found in any multicellular organism. What is the essence of phagocytosis? It is believed that it is the oldest form of protection for a multicellular organism. In the functioning of the human immune system, phagocytosis also plays a crucial role. It is the first reaction to the introduction of various viruses, bacteria and other foreign agents. Phagocytes constantly circulate throughout the body, looking for "pests". When a foreign agent is recognized, it is bound by the receptor. After that, the phagocyte absorbs the pest and destroys it.

The two main groups of mobile cells are "defenders"

Phagocytes are constantly in an active state and are ready to fight the source of infection at any time. They have a certain autonomy, since they can perform their functions not only inside, but also outside the body: on the surface of mucous membranes and in areas of damaged tissue. Human phagocytes are divided into two groups from the point of view of their effectiveness: "professional" and "unprofessional". The first include monocytes, neutrophils, macrophages, mast cells and tissue dendritic cells. The most important mobile phagocytes are white blood cells - leukocytes. They emigrate to the focus of inflammation and realize protective functions. Phagocytosis of leukocytes suggests the detection, absorption and destruction of alien objects, as well as their own dead or damaged cells. After performing its functions, some of the white blood cells move into the vascular bed and continue to circulate in the blood, and the other - undergoes apoptosis or dystrophic changes. "Nonprofessional" group consists of fibroblasts, reticular and endothelial cells, which have low phagocytic activity.

The process of phagocytosis: the first stage

Consider how the process of combating harmful organisms occurs. Scientists distinguish four stages of phagocytosis. The first is a rapprochement: the phagocyte is approaching an alien object. This happens either as a result of accidental collision, or as a result of active directional movement - chemotaxis. There are two types of chemotaxis - positive (movement towards the phagocyte) and negative (movement from the phagocyte). As a rule, positive chemotaxis is carried out to the site of tissue damage, as well as caused by microbes and their products.

Adherence of phagocytes to a foreign agent

After the proximity of the "defender" cell to the malicious particle, the second stage begins. It is sticking. The phagocyte reaches the object, touches it, and attaches itself. For example, leukocytes that have come to the inflammatory focus and adhere to the wall of the vessel, do not detach from it even in spite of the high blood flow velocity. The mechanism of adhesion is due to the superficial charge of the phagocyte. As a rule, it is negative, and the surface of phagocyte objects is positively charged. In this case, the best adhesion is observed. Negatively charged particles, for example, tumor cells, are captured by phagocytes much worse. Nevertheless, there is also sticking to such particles. It is due to the action of mucopolysaccharides present on the surface of the membranes of phagocytes, and also by reducing the viscosity of the cytoplasm and enveloping the foreign agent with whey proteins.

The third stage of phagocytosis

After adherence to an alien object, the phagocyte proceeds to absorb it, which can occur in two ways. In the place of contact, the shell of a foreign object, and then the object itself is drawn into the cell. At the same time, free edges of the membrane close over the object, and as a result a separate vacuole is formed, containing a harmful particle inside itself. The second way of absorption is the emergence of pseudopods enveloping foreign particles and closing on them. As a result, they turn out to be prisoners in a vacuole inside the cells. As a rule, with the help of pseudopodia phagocytes absorb microfungi. Retraction or enveloping of a harmful object becomes possible due to the fact that the phagocytic membrane is endowed with contractile properties.

Intracellular cleavage of the "pest"

The fourth stage of phagocytosis involves intracellular digestion. This is as follows. A vacuole containing a foreign particle includes lysosomes having a complex of digestive enzymes that are activated and poured. At the same time, an environment is formed in which the biological macromolecules of ribonuclease, amylase, protease and lipase easily decompose. Thanks to the activating enzymes, destruction and digestion occurs, and then the release of the decay products from the vacuole. Now you know what all four stages of phagocytosis are. The protection of the organism is carried out in stages: first, the phagocyte and object come together, then the attraction, that is, the location of the harmful particle on the surface of the "defender", and then - the absorption and digestion of the pest.

Unfinished and completed phagocytosis. What are their differences?

Depending on what will be the result of intracellular digestion of foreign particles, two types are distinguished: complete and incomplete phagocytosis. The first is completed by the complete destruction of the object and the removal of the decay products into the environment. Unfinished phagocytosis - what is it? The term means that foreign cells absorbed by phagocytes remain viable. They can destroy the vacuole or use it as a "soil" for reproduction. An example of incomplete phagocytosis is the absorption of gonococci in an organism that does not have immunity to them. In the unfinished process of phagocytosis pathogenic microorganisms persist inside phagocytes, and are also spread throughout the body. So, in the place of the protective mechanism, phagocytosis becomes a conductor of the disease, helping pests spread and multiply.

The causes of the disruption of the intracellular digestion process

Violation of phagocytosis occurs due to defects during the formation of phagocytes, as well as when the activity of mobile defense cells is suppressed. In addition, a negative change in intracellular digestion is possible because of hereditary diseases, such as Alder and Chediac-Higashi diseases. Violation of the formation of phagocytes, including the regeneration of leukocytes, often occurs with radioactive irradiation or because of hereditary neutropenia. Suppressing the activity of phagocytes can occur due to deficiency of some hormones, electrolytes and vitamins. Also, glycolytic poisons and microbial toxins adversely affect the functioning of phagocytes. We hope, thanks to our article, you can easily answer the question: "Phagocytosis - what is it?". Good luck!

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