Permeability - the ability of tissues, cells and subcellular structures (the nucleus of the cell, and others) to skip gases, water, and various substances. The substances to penetrate through biological membranes is passively or by active transport with participation of special mechanisms. Membrane permeability for agents depends on physical-chemical properties of the latter, and on the characteristics of membranes.
Violation of the permeability may arise as a result of various damaging factors: high and low temperature, radiation, certain substances (for example, toxins), lack of oxygen, vitamins, hormones, etc. Violation of the permeability play an important role in the pathogenesis of many disease processes: inflammation (see), allergies (see), shock (see), infectious diseases, disorders of the excretory processes and other Changes in the permeability can be the manifestation of protective reactions, and the cause of many serious disorders.

Permeability is the ability of cells and tissues to miss and to absorb liquids, and gases in the environment and to single them out. Permeability - General biological problem with relationships of an organism with the environment, with the metabolism and is essential for physiology and pathology.
There are the following theory of selective permeability of cells and tissues, different treating the substrate and conditions of this process. According to the membrane theory of cell permeability distribution of substances between the cell and the environment due to the presence of submicroscopic membrane is selectively permeable, molecules and ions. The cytoplasm of cells is considered a colloid, in which almost all the water is free and has the properties of the solvent. In the basis of sorption theory permeability is the idea of the protoplasm as water-immiscible phase, in which water and ions are bound. The intake of substances in the cell is regulated by the whole protoplasm and is determined by the factors of sorption (solubility, chemical binding, adsorption and others). In the modern view of the cell membrane (see Cell) have an overall thickness of 70-80 and consist of two parallel layers of lipid molecules oriented polar groups to the membrane surface, with adsorbed on their protein layers. In addition, in the cytoplasm there is a system of membranous formations associated with the endoplasmic network and the mitochondria.
Low-molecular substances, water, gases can enter cells under the action of osmotic forces (see the Osmotic pressure), by diffusion (see) and ultrafiltration (see), without energy costs (passive transfer). For ion permeability depends on the electric charge, the voltage difference between the outer and inner surface of the membrane.
Active migration marked the processes energy waste, generated in the cell in the process of metabolism (phosphorylation, dephosphorylation, education complex complexes the substances, the presence of molecules vectors, enzymes, and so on). This substance can move against the concentration gradient. So, the content of ions To in erythrocytes 20 times higher than the ions Na, however ions To accumulate in them, and the ions Na go into the plasma versus 50 times the concentration gradient. One of the ways of penetration of substances in the cell is pinocytes (see). This process consists in the adsorption substances cell membrane, the reduction of surface tension and vachiani into the cytoplasm with education minoritarnyh vacuoles; later their shell disintegrates, and substances included in cellular metabolism.
Selective permeability of substances depend both on the structure and chemical structure of cell membranes and sizes, electric charge, hydration, of solubility of substances in lipids. In contrast to strong acids and bases, not penetrating into the cell, weak acids and bases, which is dominated by medicationabana molecules have a large penetrating power. Shear active reaction in an acidic or alkaline side, accompanied by a change in the degree of dissociation of molecules, strengthened or weakened the substances to penetrate into the cell. So, it is established that the tertiary ammonium compounds, not to carry a charge, enter the brain, unlike ionized Quaternary amines and their salts.
In many body tissues are membranes with selective permeability (capillary endothelium and serous cavities, intestinal wall, skin cancer, etc.). The permeability of such membranes depends not only on the components of their cellular structures, but also on the permeability of the intercellular substance. Important permeability histo-hematic barriers regulating the relative constancy of the internal environment of organs and tissues (see the Barrier function).
Violation of the permeability are a critical link in the pathogenesis of many pathological processes (allergies, inflammation, swelling, shock), the mechanism of changes suction (see), secretion, excretion, metabolism. Of particular importance in clinical pathology are violations P. capillaries observed in many infectious, toxic, allergic and other diseases (dysentery, brucellosis, scarlet fever, influenza, rheumatism, and abdominal typhus fever, tonsillitis, jade and other). Violations P. vessels observed in diseases of the cardiovascular system (rheumatic pancarditis, myocarditis, septic endocardit, hypertension, atherosclerosis), respiratory system (pulmonary emphysema, pneumonia, pneumosclerosis), kidneys, liver, skin, nervous system. Changes in vascular permeability characteristic for different stages of radiation sickness.
Important in the pathogenesis of some diseases have also violations P. histo-hematic barrier. In particular, P. blood-brain barrier increases in traumatic brain injury, inflammation of the meninges, some forms of epilepsy, disturbances of cerebral circulation, shock, radiation sickness and other pathological processes. There are data on the influence of various drugs on the permeability of capillaries, the blood-brain and other histo-hematic barriers that allows you to adjust violations., in conditions of a pathology.