Semi-permeability

Semi-permeability refers to biomembrane that is selectively permeable to certain substances and cannot be passed by other substances. Semi-permeability is the basis of osmosis and characterizes the cells of all living things. Disruptions in semipermeability have devastating consequences for the electrolyte and water balance in the cell compartments.

What is the semi-permeability?

Semipermeability literally means "semi-permeability". The term stands for a property of physical or substantial interfaces. Semipermeable surfaces allow certain particles to pass while preventing others from passing.

In medical technology and biology, semipermeability plays a role especially in the context of membranes. Semipermeable membranes have selective permeability and allow certain particles to pass through the membrane in a certain direction. The corresponding membranes represent a separation system that allows certain substances to pass to the other side of the membrane without specific transport systems.

Membranes surround cells in which a specific milieu must be maintained for the sake of survival. Without the semipermeability of membranes, maintaining the specific cell environment would be inconceivable. In biology, semipermeability is also the basis for processes such as osmosis, osmoregulation and turgor.

Function & task

The term membrane transport summarizes all material penetrations through biomembrane. Membrane transport is characterized by two fundamentally different mechanisms: in addition to free permeation in the sense of diffusion, there is also specific transport.

Membrane consists of a lipid bilayer, which in itself represents a barrier between the watery compartments of the cell. The extraplasmic and cytoplasmic space are separated from each other in this way. Different milieus can prevail in the compartments. In certain biological systems, a cell membrane is permeable to smaller molecules thanks to its fluidity. This permeability exists in the biological system for water, for example, which moves along the membrane in accordance with the existing concentration gradient in the direction of the higher concentration.

This principle is a basic building block of many organisms and thus also a basis of the human organism. Semipermeable membranes are primarily permeable to solvents. Dissolved substances are often retained by the membrane in order to be able to maintain the cell environment behind the separating layer. This means that semipermeable membranes allow molecules up to a certain molar mass or size to pass through, while those above the given molar mass or size are prevented from passing through.

Science now considers temporary irregularities within the lipid bilayers of membranes to be the primary cause of semi-permeability. As the basis of osmosis, semipermeability is an important component of all living organisms. The term osmosis describes the directed flow of molecular particles through selectively permeable or semi-permeable membranes. In order to achieve a regulated water balance, the cells of all living things are dependent on osmosis and thus semi-permeability.

Semipermeability is also crucial for osmoregulation. This means the ability to regulate the concentrations of osmotically active substances in the metabolism. This ability serves to avoid osmotic stress and also helps living things to take advantage of their osmotic potential.

In addition, the semi-permeability forms the basis of the turgor pressure of plants. This pressure corresponds to a hydrostatic pressure in cells, which enables physiological processes such as gas exchange or different transport processes.

Illnesses & ailments

Systemic inflammatory responses such as sepsis can affect permeability. In this context, the mediator substance histamine is released. After the release, the permeability of the vessels increases, among other things.

Many other inflammatory responses exist that affect the membrane permeability of different tissues. One of them is pancreatitis, in which the semipermeability of the pancreatic duct system is affected by disorders. The membrane permeability of the cells decreases in this case. This phenomenon can be recognized, for example, by the penetration of X-ray contrast media during diagnostic imaging.

Further disorders of membrane permeability occur in the context of cardiovascular diseases. In most cases, all membrane permeability disorders result in an imbalance in the electrolyte balance.

Apart from the contexts described, disorders of membrane permeability can also have a hereditary basis.A hereditary mutation of membrane proteins can, for example, significantly change the permeability of a cell membrane, for example in diseases such as Myotonia congenita Thomsen.

In this disease, chloride channels within the muscles that have been altered by genetic mutation impair the membrane passage for chloride ions. Without the passage of these ions, the muscles cannot work to their full potential.

Ultimately, all membrane permeability disorders show significant effects on the entire organism. If, for example, a semipermeable membrane is suddenly no longer permeable to solvents, the water balance in the cell's compartments is out of balance. If a semipermeable membrane is again too permeable, the specific milieu of the cell compartments changes in this case too. In both cases, the affected cell can be doomed to die because the intended working environment of its compartments is out of balance.

Autoimmune diseases can also impair membrane permeability. The antiphospholipid syndrome, for example, is directed specifically against biomembrane and changes their physiological permeability.

In plants, some disturbances in membrane permeability or semipermeability of membranes associated with parasitic organisms are also observed. Certain parasites excrete wilt toxins in the sense of marasmines. These substances cause semi-permeability disturbances in order to cause an increase in permeability in the plasma of the host cell and thus to gain unhindered access.