MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY, AND PATHOLOGY - Ya.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

SECTION 4. BLOOD SYSTEM

IMMUNE DEFENSE FUNCTIONS OF BLOOD

3. PHAGOCYTOSIS

A crucial role in the nonspecific defense of the Organism is played by The phenomenon of phagocytosis, which was first described by the eminent scientist I.I. Mechnikov.

Phagocytosis (from Lat. phagos meaning "devouring") is the ability of Cells to approach, engulf, and digest foreign objects (microorganisms, foreign bodies, and tissue breakdown products).

Two MAIN TYPES OF cells possess phagocytic abilities: microphages and macrophages. Microphages include polymorphonuclear neutrophils, which belong to the so-called "professional phagocytes." Polymorphonuclear leukocytes represent a short-lived Cell population that is the first to arrive at the site of inflammation. Granulocytes produce over 10 Enzymes sufficient for the degradation of most Lipids, Polysaccharides, and Proteins of susceptible Bacteria.

Macrophages constitute the mononuclear phagocyte system. This system is distributed across various Organs and Tissues: in Connective Tissue, around the basement membranes of Blood Vessels, in the Lungs (alveolar macrophages), and in the Liver (Kupffer cells). Macrophages are capable of migration and targeted chemotaxis. Substances that determine the direction of macrophage movement are called chemoattractants. These include lymphokines, as well as degradation products of fibrin, Collagen, and cells. The sequential recruitment of various chemoattractants ensures a continuous influx of new macrophages from the vascular bed. Factors that inhibit macrophage migration and retain them at the inflammatory site—such as interferon, immune complexes, heparin, and glucocorticoids—are of great importance for neutralizing foreign agents. Conversely, sodium nucleinate and levamisole enhance macrophage migration.

For phagocytosis to occur, a microorganism must first adsorb onto The surface of a neutrophil or macrophage. A particle adsorbed on the phagocyte membrane triggers the engulfment phase, which begins with The formation of pseudopodia around it. The Plasma Membrane extends over the foreign body until it is enclosed within a vacuole (phagosome). Within a minute thereafter, The Cell's plasma granules fuse with the phagosome and discharge their contents into it.

Thus, phagocytosis comprises the following main stages:

1. Approach of the phagocyte and the microbe via positive chemotaxis.

2. Adhesion of the microorganism to the phagocyte surface.

3. Formation of pseudopodia and engulfment of the microorganism.

4. Intracellular Digestion of the foreign particle and release of breakdown products outside the cell.