Body processes

Pinocytosis – Function, Task & Diseases


The term pinocytosis derives from the Greek word “pinein”, which is translated with the German verb “to drink” and “kytos”, which means “cavity” or “cell”. Cells absorb liquids (pinocytosis) and solids ( phagocytosis ) from their surrounding medium in the form of small vesicles.

What is pinocytosis?

Two synonyms of the term are cell drinking and hydrophatocytosis . Pinocytosis takes up liquid and phagocytosis takes up solid components from the extracellular space. Both processes are summarized under the generic term endocytosis .

Liquid is absorbed into the cell plasma in the form of small bubbles with a diameter of only 150 nm. The liquid or dissolved components are absorbed into the cystole of the cells. Membrane extensions enclose the substance to be ingested, where it is absorbed as vesicles into the cell’s cystole. There it is processed enzymatically. The absorbed substances are included in the metabolism of the cells.

Pinocytosis plays an important role in the uptake of protein-bound fats into hepatocytes and enterocytes. In the reverse process, the absorbed liquids are released from the cell again. This is a biological process that is assigned to the field of cell biology (cytology).

function & task

Macromolecules and larger particles are taken up into the cells by endocytosis. This process occurs through transport vesicles (small sacs). The signaling molecules are bound to the cell surface, the cell membrane is invaginated and the contents enclosed. An endosome forms in the cell in the form of a vesicle. Thousands of these tiny bubbles now carry the charge through the cell, either for recycling or for degradation. 

This cell process enables a controlled absorption of liquids and solid substances. Thus, pinocytosis plays important roles in cell and tissue development, immune response , cell communication , and signal transduction . It is also involved in signal transmission in the neuronal areas.

Microorganisms can be warded off, although it cannot be ruled out that harmful microorganisms and viruses can get into the cells via the endocytic transmission path. Phagocytosis internalizes larger particles, for example leukocytes and macrophages . It disposes of degenerated cells, extracellular deposits and is used for food intake.

During pinocytosis, extracellular fluid is taken up together with the substances dissolved in it. Subsequently, the liquid and solutes are internalized. Medicine also refers to this process as fluid phase endocytosis .

Eukaryotic cells know four different types of pinocytosis: clathrin-dependent endocytosis, macropinocytosis, caveolae- and clathrin-independent endocytosis, and caveolae-mediated endocytosis.

In macropinone cytosis, plasma membranes fuse with long membrane protuberances, entrapment of a larger amount of extracellular fluid. Clathrin-dependent endocytosis internalizes extracellular molecules. Substances important for the human organism, such as iron , are absorbed through this process. A caveolae is a bottle-shaped invagination of the plasma membranes. It fulfills many functions within the cell and is responsible for signal transduction. The internalization of the caveolae within the cells is slow. For this reason, caveolae-mediated endocytesis takes up only small amounts of extracellular fluid. Clathin-independent mechanisms are in neuronsand neuroendocrine cells, where they support the reuptake of proteins into the plasma membrane.

With the reverse process of exocytosis , the vesicle is released from the cell again. The word component “exo” means “out”. The membrane of a sac (vesicle) fuses with a cell membrane, allowing the substance absorbed by the sac to escape. This process is stimulated by certain membrane receptors.

Some cells are able to internalize 25 percent of their membrane, always returning the same amount of membrane. This process mostly occurs through clathrin-coated vesicles fusing with endosomes. Lipid membranes form the basis for the vesicles that close off a lumen (inner space of a cell). By pinching off cell compartments, the vesicles migrate to their destination to fuse with the cell membrane. Proteins assist in this process by pinching off a vesicle from a flat membrane.

Diseases & Ailments

In pinocytosis, ingested food is first absorbed by droplets into a surrounding medium in the food vacuole. Digestion of ingested food begins by lysosomes (sacs) containing digestive enzymes based on fusion between membrane and food vacuole. Pinocytosis transfers the digested food from the digestive vacuole to the cell’s plasma. Food residues that cannot be digested are transported to the cell membranes by means of a defecation vacuole and emptied to the outside.

If this process is disrupted, various diseases can occur that are attributed to a defect in membrane transport. Dementia , Alzheimer’s , metabolic disorders , increased cholesterol levels , neurological diseases (limited muscle reflexes, sensory disturbances ), Huntington’s disease (death of nerve cells), personality changes and various types of physical and mental disabilities, such as Charcot-Marie-Tooth neuropathy syndrome related to defective pinocytosis.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.