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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."
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.
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 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
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"
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
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