light, biological effect

From Big Medical Encyclopedia

LIGHT — the electromagnetic radiation having wave and corpuscular (quantum) properties, extending in space with maximum speed to 300 000 km/s. In practice understand the electromagnetic radiation of limited range of lengths of waves or a range causing at action on biol as S. objects response specific reaction.

It is accepted to allocate the following spectral regions of S.: distant ultra-violet (length of waves of 10 — 200 nanometers), near ultra-violet (200 — 400 nanometers), seen (400 — 760 nanometers), near infrared (760 — 2500 nanometers), average (2500 — 50 000 nanometers) and distant (St. 50 000 nanometers) infrared areas. Page of narrow, strictly narrow spectral structure or lengths of waves is called monochromatic.

The science studying properties C. and its interaction with substance is called optics (see). A research of the general patterns and mechanisms of action of S. on biol. objects is engaged photobiology (see). The fundamental law of photobiology is that biol. the effect causes S. only of such wavelength, at a cut it is absorbed by molecules of cells, and existence of photo biological effect unambiguously indicates presence at cells of the molecules absorbing light quantums of this spectral range.

After absorption of quantum of S. of a molecule turn into excited state with the increased reactivity and enter chemical interaction with the next molecules (see. Luminescence , Molecule ). All set of photobiological responses can be divided into three groups: biopower, regulatory and destructive. During biopower reactions there is a transformation of electromagnetic energy of S. to energy of chemical bonds of organic compounds. The most studied reactions of this type happen in process photosynthesis (see). During photoregulatory reactions the organism obtains necessary information on state of environment. At the same time there is no accumulation of energy in the quantities essential to power of an organism, and S. is used as the trigger — the mechanism starting the intracellular reactions bringing to biol. to effect at organismic level (see. Trigger mechanisms ). An example of reaction of this type are the reactions which are the cornerstone sight (see). At plants and microorganisms the wide range of various photoregulatory reactions is found and rather in detail investigated. It is known that development of plants is controlled along with other mechanisms and the fitokhromny system responsible for germination of seeds, transition of plants to blossoming, fructification, their reaction to duration of lighting within a day, etc. Reactions of the induced synthesis of the pigments performing protective function are found in microorganisms. Many mobile forms of microorganisms have ability to change the direction of the movement in relation to S.'s source (reaction of a phototaxis). Ability of enzymes to change the activity under the influence of S. of a certain wavelength is the cornerstone of many photoregulatory reactions.

Destructive action of S. consists in damage of bioorganic molecules with subsequent change of function of cells (see. Photochemical reactions ). The so-called lethal, leading to death of microorganisms at action Uv-radiations are among such reactions. The mechanism of lethal action of Uv-radiation photochemical damage nucleinic to - t is the cornerstone, of proteins and lipids of cellular membranes. Many organisms possess the photobiological systems of photoreactivation and photoprotection reducing efficiency of lethal action of Uv-radiation. A special kind of lethal reactions is the photodynamic effect consisting in destruction of cells by visible S. or near Uv-radiation at introduction to a cell of dye, napr, methylene blue, haematoporphyrin, etc. (see. Fotosensibilization ), process proceeds only in the presence of molecular oxygen. It is necessary to consider that molecules of many substances, including being a part of food stuffs and pharmaceutical means possess the photosensitizing action (see. the Photosensitizing means ). Haematoporphyrins of blood, streptocide, Sulfidinum, vitamins of group B, quinine, quinacrine, many antibiotics are among such substances (chemical connections). Therefore it is necessary to control, and if necessary and to limit duration of stay of the patient in the sun after the use of these connections.

It is known that long stay without S. leads to a complex of the painful phenomena which are followed by disturbance of life activity of a human body — so-called. to light starvation (see). At the same time can develop rickets (see), a hypovitaminosis (see. Vitamin deficiency ), caries (see. Caries of tooth ), diseases of a nervous system, etc. Against the background of the general weakening of an organism development is facilitated tuberculosis (see), recovery processes are slowed down, the general body resistance decreases.

Along with the expressed negative effects of action of S. a large number of the facts speaking about its salutary impact on the general condition of an organism is saved up for an organism. So, at solar S.'s action the quantity of uniform elements of blood changes and its coagulability increases, the content of carbohydrates and fats is normalized; The Page causes also a trichangiectasia in skin, Ur-zheniye of pulse, decrease in level of blood pressure. S.'s action well affects activity of hormonal system of animals and the person; seasonality in sexual activity at many animals as S. stimulates production of gonadotropic hormones is explained by reaction to change of duration and intensity of illumination.

S.'s use in medicine is based first of all on its fortifying action (see. Phototherapy ). Along with the general illumination of a body of the person apply as well local impact on certain sites. At the same time it is necessary to control strictly the wavelength of S., an exposure dose and biol. effect to consider existence of such contraindications to phototherapy as malignancies, nephrite, active forms of a pulmonary tuberculosis, atherosclerosis, eczema, a thyrotoxicosis, bleedings, inflammatory processes etc. Skin of the person possesses defense reaction to action of Uv-radiation due to formation of a special pigment of melanin (see. Melanina ).

Along with therapeutic use of S. found also other application in medical practice. Ultraviolet radiation (see) use for air sterilization in operational and dressing rooms. Laser radiation is applied in ophthalmology and surgery (see. Lasers, in medicine ). Optical techniques of diagnosis of various diseases and a lab are developed. analyses (see. Polarimetry , Refractometry , Refractometry of an eye , Spectral analysis etc.).

Bibliography: Konev S. V. and Bolotovsky I. D. Photobiology, Minsk, 1979; Rubin JI. B. The laser equipment in modern biology, M., 1978.

L. B. Rubin.