Endocytózou

Endocytózou, known in English as endocytosis, is a cellular process by which cells internalize extracellular material through the formation of vesicles from the plasma membrane. This mechanism enables nutrient uptake, regulation of receptor signaling, and defense against pathogens.

There are several major pathways. Phagocytosis involves the uptake of large particles by specialized cells such as macrophages and neutrophils; material is enclosed in a phagosome that later fuses with lysosomes for degradation. Pinocytosis covers the non-specific uptake of fluids and solutes, including macropinocytosis, which forms larger vesicles. Receptor-mediated endocytosis is highly selective: ligand binding to cell-surface receptors promotes the formation of clathrin-coated pits and vesicles, with dynamin driving scission; the vesicles then reach early endosomes. Caveolin-mediated endocytosis uses caveolae, cholesterol-rich membrane domains, as carriers and represents another distinct route for certain lipids and proteins.

Mechanistically, internalized vesicles shed their coats and traffic to endosomal compartments. Cargo is sorted in early endosomes: some is sent to lysosomes for degradation, while others are recycled back to the plasma membrane via recycling endosomes. Endosomal maturation proceeds from early to late endosomes, often involving Rab GTPases, and may culminate in fusion with lysosomes.

Functions and significance include nutrient uptake (for example, transferrin and low-density lipoprotein receptors), regulation of signaling by removing surface receptors, and roles in antigen processing and presentation in the immune system. Pathogens can exploit endocytosis to enter cells, and dysregulation of endocytic pathways is linked to various diseases, highlighting its central role in cell physiology.