Barrier Function

the ability of the human or animal organism to protect its internal environment (blood, lymph, tissue fluid) from external influences and to maintain the relative constancy (homeostasis) of its composition of chemical, physical and biological properties by means of special physiological mechanisms called barriers. External barriers (the skin, mucous membranes, and the respiratory, excretory, and digestive apparatus) are conventionally distinguished from internal barriers—histological and hematological barriers located between the blood and the tissue fluids (extracellular fluids) of organs and tissues. Among the external barriers the most important is the hepatic barrier which neutralizes poisonous compounds formed in the intestine and released by it into the blood. The barrier function determines to a large extent the life functions of organs and tissues, as well as their sensitivity to bacteria, poisons, toxins, products of a disturbed exchange of substances, foreign substances, and medicines. The plasticity of the external and internal barriers, their adaptability to changing conditions in the environment, are essential for the normal existence of the organism and its protection against disease, intoxication, and so on. The most detailed studies have been made of such barriers as the hematencephalitic barrier (between the blood and the brain), the hematophthalmic barrier (between the blood and the tissues of the eye), and the placental barrier (between the organism of the mother and the embryo). Work by Soviet scientists (such as L. S. Shtern, A. A. Bogomol’-ets, B. N. Mogil’nitskii, and A. I. Smirnovaia-Zamkovaia) has contributed greatly to knowledge of the barrier function.