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Aquaporins are "the plumbing system for cells". Water moves through cells in an organized way, most rapidly in tissues that have aquaporin water channels. [28] For many years, scientists assumed that water leaked through the cell membrane, and some water does. However, this did not explain how water could move so quickly through some cells. [28]
In this system a semipermeable membrane separates two solutions of different concentration of the same solute. If the membrane allows the passage of water but not the solute the water will move into the compartment with the greatest solute concentration in order to establish an equilibrium in which the energy of the system is at a minimum. This ...
Exocytosis and its counterpart, endocytosis, the process that brings substances into the cell, are used by all cells because most chemical substances important to them are large polar molecules that cannot pass through the hydrophobic portion of the cell membrane by passive transport. Exocytosis is the process by which a large amount of ...
An increase in cytosolic Ca2+ concentration will reversibly limit passage through the plasmodesmata. Unlike gap junctions, the cell membranes of adjacent cells merge to form a continuous channel called an annulus. Additionally, within the channel, there is an extension of the endoplasmic reticulum, called a desmotubule, which spans between the ...
Cell junctions are also especially important in enabling communication between neighboring cells via specialized protein complexes called communicating (gap) junctions. Cell junctions are also important in reducing stress placed upon cells. In plants, similar communication channels are known as plasmodesmata, and in fungi they are called septal ...
The human body consists of biological systems, that consist of organs, that consist of tissues, that consist of cells and connective tissue. The history of anatomy has been characterized, over a long period of time, by a continually developing understanding of the functions of organs and structures in the body.
In contrast, paracellular transport is the transfer of substances across an epithelium by passing through an intercellular space between the cells. It differs from transcellular transport, where the substances travel through the cell passing through both the apical membrane and basolateral membrane; Renal physiology. Transcellular transport is ...
The constrained intracellular pathway exacted by the tight junction barrier system allows precise control over which substances can pass through a particular tissue (e.g. the blood–brain barrier). At the present time, it is still unclear whether the control is active or passive and how these pathways are formed.