Paracellulaariselle

Paracellulaariselle is a Finnish term that translates to "paracellular" in English. It refers to the pathway for substances to move across a cellular layer, such as an epithelium or endothelium, by passing through the tiny spaces between adjacent cells, rather than directly through the cells themselves. This paracellular route is distinct from the transcellular pathway, which involves substances crossing the cell membrane, traversing the cytoplasm, and exiting through another membrane.

The paracellular pathway is regulated by tight junctions, which are protein complexes that seal the space between cells. These junctions can be selectively permeable, controlling which molecules can pass through. The degree of tightness varies depending on the specific tissue and its function. For example, in the blood-brain barrier, tight junctions are very restrictive, limiting the passage of most substances into the brain. In contrast, in the small intestine, paracellular permeability is higher to allow for the absorption of nutrients.

Factors influencing paracellular transport include the size and charge of the molecule, the tightness of the tight junctions, and the pressure gradients across the cellular layer. This pathway is crucial for the movement of ions, water, and small molecules, playing a significant role in processes like nutrient absorption, waste removal, and maintaining tissue homeostasis. Understanding paracellular transport is important in various fields, including physiology, pharmacology, and disease pathology.