What is phagocytosis and why is it needed
The term phagocytosis is of Greek origin. It is formed by combining two words: phagos, which translates as "eating", and cytos, which translates as "cell". This fundamental biological phenomenon was discovered by I.I. Mechnikov in 1882.
The biological significance of this process varies drastically depending on the level of organization of the living organism:
- In unicellular organisms. For such protozoan creatures as amoebas, this process is a vital method of nutrition.
- In multicellular organisms. Here the process acquires a completely different meaning and performs a crucial protective function. This task is undertaken by phagocytes — specialized cells of the multicellular organism that engulf foreign agents to protect the entire body.
Main stages of phagocytosis
The process of engulfing foreign particles represents a complex cascade of events and includes several strictly sequential stages:
- Approaching. At the very first stage, the object of phagocytosis (which, for example, can be a bacterium) and the phagocyte itself approach each other.
- Adhesion. Once contact is established, the attachment stage begins. The bacterium is located directly on the surface of the phagocytic cell.
- Ingestion. The phagocyte cell membrane begins to surround the bacterium from all sides, after which it actively draws it inside the cytoplasm.
- Phagosome formation. Inside the cytoplasm, a specialized structure is formed — a separate vesicle containing the engulfed object.
- Digestion. At the final stage, active hydrolytic enzymes are delivered from specialized structures — lysosomes. It is they that ultimately break down the captured bacterium.
Pinocytosis and its features
Another important membrane process — pinocytosis — also plays a huge role in vital activity. The main distinguishing feature of this process is that it is most characteristic of cells distinguished by intensive metabolism.
Several key zones can be identified in the body where this process proceeds most actively. The main localization includes:
- Cells of the lymphatic system.
- Intestinal epithelial cells.
- Endothelium of blood capillaries.
Briefly: answers to topical questions
What is the main difference between pinocytosis and phagocytosis in terms of the physical state of the ingested substance?
The main difference lies in the physical state of the captured substrate.
| Process | State of the ingested substance |
|---|---|
| Phagocytosis | Capture and transport of solid particles (dense, large particles) |
| Pinocytosis | Capture and uptake of liquid media (solutions of substances within a droplet) |
Which molecules and receptors provide the adhesion stage in phagocytosis?
The adhesion stage is provided by specialized molecules and receptors on the surface of interacting cells.
- Target cell factors — opsonins (antibodies, C3b, fibronectin) and adhesion molecules (immunoglobulin superfamily ICAM-1 and ICAM-2).
- Phagocyte factors — adhesion molecules (including integrins, e.g., LFA-1) and specific receptors for opsonins (FcγR, C3R).
Which cytoskeleton elements provide the drawing of the bacterium into the cytoplasm during the ingestion stage?
The drawing of the bacterium into the cytoplasm during the ingestion (immersion) stage is provided by cytoskeleton elements represented by microfilaments.
The basis of these structures is polymerized filamentous F-actin, which is the main contractile protein of the cell. The mechanism of movement and wrapping of the object is based on the interaction of actin microfilaments with myosin, their shortening and elongation.
What are the main types of professional phagocytes in the human body?
The main "professional" phagocytes are monocytes and macrophages. Tissue-specific resident macrophages are represented by the following main types:
- Kupffer cells — localized in the liver.
- Alveolar macrophages — in the lungs.
- Peritoneal macrophages — in the abdominal cavity.
- Microglia — in the central nervous system.
- Mesangial cells — in the kidneys.
- Osteoclasts — in bone tissue.
To easily remember the stages of phagocytosis in order, use the abbreviation "SAPOP": Approaching (Sblizhenie), Adhesion (Adgeziya), Phagocytosis/Ingestion (Pogloshchenie), Formation (of phagosome), Digestion (Perevarivanie).
Class and exam questions
Who discovered the phenomenon of phagocytosis and when?
This process was discovered by the Russian researcher I.I. Mechnikov in 1882.
What is the difference in the biological role of phagocytosis between amoebas and humans?
For unicellular organisms (such as amoebas), this is the main method of nutrition. In a multicellular organism, phagocytes perform an exclusively protective function.
Where do the enzymes for digesting bacteria come from?
Hydrolytic enzymes necessary for breaking down the engulfed object come from specialized cell organelles — lysosomes.
For which cells is pinocytosis most characteristic?
It is typical for cells with intensive metabolism: intestinal epithelial cells, blood capillary endothelium, and lymphatic system cells.
What else to study on this topic
- Detailed mechanisms of approach between the phagocyte and the object
- The role of the cell membrane in adhesion and ingestion
- Structure and functions of the resulting phagosome
- Features of the action of lysosomal hydrolytic enzymes
- Intensive metabolism in intestinal epithelial cells
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