Pinocitosi

Pinocitosi, also known as cell drinking, is a form of endocytosis in which cells internalize small droplets of extracellular fluid along with dissolved substances. This process allows cells to uptake nutrients, hormones, and other molecules that are present in the surrounding environment. Pinocitosi is a non-specific mechanism, meaning that it does not select particular molecules but engulfs whatever is available in the extracellular fluid.

The process begins with the formation of small, irregular invaginations of the plasma membrane. These invaginations deepen to form vesicles that contain the fluid and dissolved substances. Once inside the cell, these vesicles are released into the cytoplasm where their contents can be processed and utilized. Pinocitosi occurs continuously at low levels in most cell types, playing an essential role in maintaining cellular homeostasis and nutrient uptake.

Compared to other forms of endocytosis such as phagocytosis, which involves the engulfment of large particles or cells, pinocitosi is characterized by its small vesicle size and non-selective nature. It is often considered a fundamental cellular process in tissues requiring constant internalization of extracellular fluids, like endothelial cells and certain epithelial cells.

This process is energy-dependent, involving the rearrangement of the cytoskeleton and the activity of various proteins that facilitate vesicle formation and trafficking. Pinocitosi contributes significantly to cellular functions such as nutrient acquisition, regulation of extracellular fluid composition, and receptor recycling. Its significance is particularly evident in physiological contexts like blood vessel maintenance, immune responses, and tissue remodeling.