Radiant energy from the sun. Action of radiant energy Use of radiant energy
Radiant energy is the totality of all electromagnetic waves that arise and propagate in space at a speed approaching 300 thousand km/s. The pathological effect on the body is primarily exerted by radiation, which can cause ionization in tissues. Moreover, the pathogenic effect of rays is inversely proportional to their wavelength.
Different types of radiant energy have different effects. In some cases, radiant energy, absorbed by tissues, turns into heat, resulting in overheating of animals; in others, it has a chemical effect on tissues, causes a number of chemical transformations in the body, and gives the so-called photochemical effect.
In the occurrence of pathological processes in the body, solar rays and, first of all, ultraviolet radiation from the solar spectrum can play a certain role. These rays have a chemical effect, and the shorter the wavelength, the more intense they are. The effect of rays on the body depends on the duration of action, their angle of incidence, the thickness of the atmospheric layer through which the rays pass, as well as on the permeability of tissues and the general reactivity of the body. With prolonged exposure to ultraviolet rays, an animal's blood vessels dilate, blood pressure drops, metabolism (mainly protein) is disrupted, and tissue breakdown processes intensify.
With intense and prolonged irradiation of large parts of the body, the animal may experience severe hemodynamic disorders - such as shock, which sometimes even leads to death. The pathogenic effect of ultraviolet rays on the central nervous system develops in two directions: on the one hand, its activity is inhibited due to irritation of the receptor apparatus (rays and toxic products of tissue decay); on the other hand, there is a toxic effect on it (humorally) of irradiated cholesterol and protein-lipid complexes of the blood.
Long waves of the solar spectrum, red and infrared rays have a thermal effect on the body. From the excessive action of these rays, the body overheats or burns of varying degrees occur.
Under the influence of direct sunlight, if they fall on an animal's unprotected head, sunstroke may occur. In this case, the blood vessels of the central nervous system (meninges) dilate and the vasomotors are damaged. Sometimes there are ruptures of capillaries and hemorrhages into the nervous tissue. At first, the animals become very excited, their breathing and pulse quicken, convulsions begin, then the stage of depression begins. Animals often die from paralysis of the respiratory or circulatory centers. The effect of sunlight on the body may not occur immediately, but after several hours, that is, when the ultraviolet chemical part of the spectrum begins to exert its effect. Unlike heatstroke, sunstroke does not necessarily require preliminary overheating of the body: an increase in body temperature during sunstroke is considered a secondary factor as a result of irritation of the nervous heat-regulating centers. Dysfunction of higher nerve centers and stimulation of the cerebral cortex during sunstroke are more variable and persistent than during heatstroke.
Laser radiation. The laser is capable of emitting monochromatic beams of light with a small divergence angle. The rays act on the tissue for a very short period of time (hundred-thousandths of a second), they are absorbed by pigmented tissues, red blood cells, melanomas, etc. Laser rays destroy living tissue, tumors are especially sensitive to them. Damage to a biological object occurs as a result of the thermal effect of the beam on tissue and their absorption of thermal energy. Toxic substances are simultaneously formed in tissues and cells and the action of tissue enzymes changes. In addition, mechanical action is possible due to the instantaneous transition of solid and liquid substances into a gaseous state and an increase in intracellular pressure (up to several tens and hundreds of atmospheres).
Effect of ionizing radiation. The main source of ionizing radiation is X-ray and radioactive. The biological effect of this radiation depends on many factors: the type of radiation, the dose of general or local exposure, external or internal exposure, single or repeated, as well as on the individual and species sensitivity of the body.
Different tissues have different sensitivity to radiation exposure. According to the degree of damage, they can be arranged as follows: hematopoietic organs, intestinal glands, epithelium of the genital organs, epithelium of the skin and lens, endothelium, fibrous tissue, internal epithelial organs, cartilage, bones, muscles, nervous tissue. Functional and structural changes in the nervous system, observed during radiation exposure, lead to disruption of the regulation of the activity of the entire organism, to a decrease in its resistance to infectious diseases.
Radiation sickness is a general damage to the body as a result of the action of large doses of ionizing rays. It occurs both due to external exposure to radiation (in an accident during work with generators capable of producing ionizing radiation, during an atomic explosion, during improper use of radiation therapy), and during internal exposure (when various radioactive substances enter the body with food or inhaled air). - substances).
The course of radiation sickness can be acute (when the body is exposed to large doses of ionizing radiation) and chronic (the body is affected by small doses, but for a long time).
Long-term consequences of ionizing radiation are their carcinogenic effects and damage to the chromosomal apparatus of germ cells. In case of severe radiation injuries, as a result of a decrease in the body's resistance, autoinfection is noted, and in case of accumulation of toxic substances in the blood, the phenomenon of toxicity is observed.
The action of electricity.
The pathological effect of electrical energy on the animal’s body will occur if it is in direct contact with a current-carrying object or if the body has been subjected to discharges of atmospheric electricity (during a lightning strike). Pathological changes in the body depend on the properties of the electric current, the reactivity of the body and its tissues, as well as on a number of particular accompanying factors. The effect of electric current on the body is determined by its voltage and strength, the duration of exposure, the nature of the current (direct, alternating), tissue resistance, the direction of the current and the individual characteristics of the animal. The pathogenicity of the current is also determined by the duration of its passage through the body; with increasing duration of the current, its harmfulness also increases .
The effect of electric current depends on the vital importance of the organs through which it passed. It is most dangerous for life if the current passes through the heart. Slow and irreversible paralysis occurs, the phenomena of atrial fibrillation of the ventricles develop, and cardiac arrest occurs in diastole. The nerve centers of some animal species are less sensitive to electric current compared to the heart.
There are local and general effects of electric current. With local action, a burn is obtained, sometimes having the shape of the conductor that had its effect. At the site where the current enters and exits the body, wounds form, and around them, due to paralysis of the skin vessels, branched red figures appear. After some time (several days, weeks) after exposure to electric current, necrosis of the outer integument and underlying tissues is often observed at the site of the lesion. Sometimes small grayish-white solid oval or round areas, bordered by roller-like elevations, remain on the skin. These are the so-called electric signs; Histologically, they have the appearance of palisade-shaped cells of the Malpighian layer of the skin. These same tissues are characterized by a cellular structure, and in some cells there is gas, apparently formed as a result of the electrochemical action of the current.
With the general effect of electric current, the nervous and cardiovascular systems are primarily affected. Changes in the central nervous system occur in two phases: in the form of short-term excitation and longer-term depression, or inhibition. The excitation phase is sharply expressed under the influence of a small current. When passing a current of 100 A and higher, the excitation phase is very short, but it is quickly followed by an inhibition phase, often manifested by a drop in blood pressure and cessation of breathing. As a result, the so-called imaginary death occurs.
Violation of blood circulation and breathing during electrical trauma also occurs in two phases. In the first phase, arterial and venous pressure increases, breathing quickens. Changes in hemodynamics and breathing rhythm are caused by electrical stimulation of the receptor gel, as well as convulsive contraction of striated muscles. When blood pressure rises, heart contractions become slower due to irritation of the vagus nerve by current. In the second phase, which occurs quite quickly, blood pressure drops sharply and breathing stops.
In animals that have suffered electrical trauma, severe damage to the nervous system, paralysis of striated muscles, damage to the intestines, bladder, kidneys, edema, and dropsy of the joints are noted. The consequences of electrical trauma also depend on the initial functional state of the central nervous system, as evidenced by the fact that in anesthetized animals the effect of electric current is reduced. A strong electric current can cause a state of tissue parabiosis; This, in all likelihood, is due to the absence of pain in the affected tissues.
The mechanism of action of electric current. Electric current acts on the body in three directions: electrochemical, electrothermal and electromechanical.
Electrochemical action is expressed in the occurrence of the process of electrolysis in tissues, in the disruption of their colloidal structures; In particular, fatty acids are formed from the decomposition of sebum. The electrochemical process causes the formation of electrical marks at the entry and exit points of the electric current.
Electrothermal action is caused by the fact that electrical energy, having passed through the tissues of the body, turns into thermal energy (Joule heat). Especially a lot of heat is generated when a high voltage current passes through bone tissue, which is why so-called bone beads appear on the bones; they are white, spherical or ovoid in shape, the size of a millet grain or pea, consist of phosphate of lime with its subsequent transformation (after stopping the current and cooling the mass) into a solid. The increase in tissue temperature is especially noticeable at the sites of current entry and exit; it causes irritation of nerve receptors, resulting in pain and reflex dysfunction of various organs. When an electrical injury occurs, body temperature also increases.
Electromechanical action caused by the direct transition of electrical energy into mechanical energy, as well as by the action of gas and steam formed at the site of injury; These factors cause structural changes in tissues such as incised wounds, fractures, bone trabeculae, etc.
The action of atmospheric electricity (lightning). A lightning strike to the head usually results in death from respiratory paralysis. Local changes caused by a lightning strike include burns with tissue rupture; red zigzag shapes appear on the outer skin due to paralysis of the vascular nerves and the vessels themselves. Ulcers caused by lightning strikes do not heal well. Non-fatal lightning strikes include loss of consciousness, convulsions, and sometimes permanent paralysis.
Related information.
It is no coincidence that we begin the review with this environmental factor. Radiant energy from the sun, or solar radiation, is the main source of heat and life on our planet. Only thanks to this, in the distant past on Earth, organic matter could have arisen and, in the process of evolution, reached those degrees of perfection that we observe in nature at the present time. The main properties of radiant energy as an environmental factor are determined by wavelength. On this basis, within the entire light spectrum, visible light, ultraviolet and infrared parts are distinguished (Fig. 10). Ultraviolet rays have a chemical effect on living organisms, while infrared rays have a thermal effect.
Rice. 10. Spectra of solar radiation c. various conditions (after: Odum, 1975).
1 - not changed by the atmosphere; 2 - at sea level on a clear day; 3 - passed through continuous clouds; 4 - passed through the vegetation canopy.
The main parameters of the environmental impact of this factor include the following: 1) photoperiodism - a natural change in light and dark time of day (in hours); 2) lighting intensity (in lux); 3) voltage of direct and scattered radiation (in calories per unit surface per unit time); 4) chemical action of light energy (wavelength).
The sun continuously emits enormous amounts of radiant energy. Its power, or radiation intensity, at the upper limit of the atmosphere ranges from 1.98 to 2.0 cal/cm 2 -min. This indicator is called the solar constant. However, the solar constant, apparently, can vary somewhat. It is noted that in recent years the brightness of the Sun has increased by approximately 2%. As it approaches the Earth's surface, solar energy undergoes profound transformations. Most of it is retained by the atmosphere. Further, vegetation gets in the way of the light waves, and if it is a multi-tiered closed tree plantation, then a very small part of the initial solar energy reaches the soil surface. Under the canopy of a dense beech forest, this amount is 20-25 times less than in the open. But the point is not only a sharp decrease in the amount of light, but also that in the process of penetrating deep into the forest, the spectral composition of the light changes. Consequently, it undergoes qualitative changes that are very significant for plants and animals.
Speaking about the ecological significance of light, it must be emphasized that the most important thing here is its role in the photosynthesis of green plants, because the result is the creation of organic matter, plant biomass. The latter represents the primary biological production, on the use and transformation of which everything else living on Earth depends. The intensity of photosynthesis varies greatly in different geographical areas and depends on the season of the year, as well as on local environmental conditions. Additional lighting can significantly increase the growth of even tree and shrub species, not to mention herbaceous plants. I. I. Nikitin germinated acorns for 10 days under continuous light, then 5 months. I grew seedlings in light with a brightness of 4 thousand lux. As a result, the oak trees reached a height of 2.1 m. After transplanting into the ground, the 8-year-old experimental oak tree gave an annual increase in height of 82 cm, while the control trees - only 18 cm.
It is noteworthy that although the vital activity and productivity of animals are in direct (for phytophages) or indirect (for zoophages) dependence on the primary production of plants, nevertheless, the connection between the latter and animals is far from one-sided. It has been established that phytophagous animals, such as moose, by eating green plant matter and damaging photosynthetic organs, are capable of
significantly reduce the intensity of photosynthesis and plant productivity. Thus, in the Central Chernozem Reserve (Kursk region), moose ate only 1-2% of the phytomass of young oak forests, but their productivity fell by 46%. Thus, in the system of food plant - phytophage, there is both direct and feedback.
Photoperiodism plays a huge role in the life of all living beings. As this factor is studied, it becomes clear that the photoperiodic reaction underlies many biological phenomena, being a direct factor determining them or performing signaling functions. The outstanding importance of the photoperiodic reaction is largely due to its astronomical origin and, therefore, a high degree of stability, which, for example, cannot be said about the temperature of the environment, which is also extremely important, but extremely unstable.
The very fact of dividing animals into two large groups according to the time of activity - daytime and night - clearly indicates their deep dependence on photoperiodic conditions. The same is evidenced by the pattern established in 1920 by American scientists W. Garner and G. Allard, according to which plants, in relation to light and temperature, are divided into long- and short-day species. Later it was found that a similar photoperiodic reaction is also characteristic of animals and, therefore, is of a general ecological nature.
The regular change in the length of daylight hours over the seasons determines the time of onset of diapause for numerous species of insects and other arthropods, in particular mites. Through subtle experiments, A. S. Danilevsky and his colleagues proved that diapause is stimulated precisely by the shortening of the day, and not by a decrease in air temperature, as previously thought (Fig. 11). Accordingly, the natural increase in the duration of daylight hours in the spring serves as a clear signal for the termination of the diapause state. At the same time, species populations living at different latitudes differ in specific photoperiodic requirements. For example, for the dock butterfly (A crony eta rumicis), in Abkhazia a day length of at least 14 hours 30 minutes is required, in the Belgorod region - 16 hours 30 minutes, in the Vitebsk region - 18 hours and near Leningrad - 19 hours. In other words, With every 5° latitude moving north, the length of day required to exit diapause in this species lengthens by about an hour and a half.
Rice. 11. Photoperiodic reaction of the long-day type - the cabbage butterfly (1) and the short-day type - the silkworm (2) (after: Danilevsky, 1961).
Thus, photoperiodism is a major factor in the seasonal activity of arthropods. Moreover, similar studies by botanists have shown that many phenomena in the seasonal life of plants, the dynamics of their growth and development also relate to photoperiodic reactions. For example, the photoperiodic factor serves as a signal for early preparation of plants for winter, regardless of weather conditions. All this makes photoperiodism a very significant factor when introducing agricultural plants into new areas, when cultivating them in greenhouses, etc.
Finally, a comparison of the results of experiments on the photoperiodism of phytophagous insects and their food plants revealed a deep interdependence between them. Both respond to the influence of the same environmental factor in a similar way; therefore, their trophic connections have a deep ecological and physiological basis.
The study of photoperiodic reactions of higher vertebrates also brought extremely interesting results. Thus, fur-bearing animals develop increasingly thick and luxuriant hair in the fall. In winter, it reaches its greatest development and maximum thermal insulating properties. These protective functions of the fur are enhanced by the thick layer of fat that forms under the skin in late summer and fall. In winter, the mentioned morphophysiological adaptations function fully. It has long been believed that the main factor determining the seasonal development of fur and fat is air temperature, its drop in the autumn-winter months. However, experiments have demonstrated that the triggering mechanism for this process is associated not so much with temperature as with photoperiodism. In a laboratory vivarium and even on a fur farm, you can place American minks or other animals in cages with controlled lighting and, starting in mid-summer, artificially reduce daylight hours. As a result, the molting process in experimental animals begins much earlier than in nature, will proceed more intensely and, accordingly, will end not by winter, but at the beginning of autumn.
The photoperiodic basis also underlies the most important seasonal phenomenon in the life of migratory birds - their migration and the closely related processes of molting plumage, accumulation of fat under the skin and on internal organs, etc. Of course, all of these are adaptations to endure unfavorable temperature and feeding conditions by “ avoiding them. However, in this case, the main signaling role is played not by changes in temperature, but by light conditions - a reduction in the length of the day, which can be proven through experiments. In the laboratory, acting on the photoperiodic response of birds, it is not too difficult to bring them into a specific pre-migratory state, and then into migratory excitement, although the temperature conditions will remain stable.
It turns out that the cyclical nature of animal sexual activity and the cyclical nature of their reproduction are also photoperiodic. Perhaps this is especially surprising, since the biology of reproduction belongs to the properties of the organism that are most finely formed and have the most complex coordination of relationships.
Experiments on many species of birds and mammals have proven that by increasing the duration of daylight hours, it is possible to activate the gonads (Fig. 12), bring animals into a state of sexual arousal and achieve productive mating even in the autumn-winter months, if, of course, there is a positive reaction to light both sexes will find the impact. Meanwhile, females in some species (for example, sparrows) in this regard turn out to be much more inert than males and require additional ethological stimulation.
Rice. 12. The influence of light on the development of gonads in male and female house sparrows killed after being kept under different conditions (after: Polikarpova, 1941).
a - from freedom on January 31; b - from a room temperature chamber on January 29; c - from a chamber with additional light on January 28.
Some mammals - sable, marten, a number of other species of mustelids, as well as roe deer - have an interesting feature of reproductive biology. In them, the fertilized egg is not first implanted into the uterine wall, but<в течение длительного времени находится в состоянии покоя, так называемой латентной стадии. У соболя эта стадия продолжается несколько месяцев и лишь приблизительно за полтора месяца до рождения щенков происходит имплантация яйца и очень быстрое эмбриональное развитие. Таким образом, беременность распадается как бы на длительный период предбеременности, или латентный, и короткий, порядка 35-45 дней, период вынашивания, т. е. собственно эмбрионального развития. Благодаря этому замечательному приспособлению животные получают возможность с минимальными энергетическими затратами переживать тяжелое зимнее время. Оказывается, что продолжительность латентного периода также регулируется фотопериодической реакцией и, если воспользоваться последней, может быть существенно сокращена.
The influence of the ratio of periods of light and darkness and changes in light intensity throughout the day on the activity of animals is very large. For example, diurnal birds awaken at dawn at a “waking illumination” of a certain intensity, depending on the height of the sun relative to the horizon. The onset of proper “wake-up illumination” serves as a signal that stimulates the birds to become more active. Blackbirds begin to show signs of life at 0.1 lux, when the forest is still almost completely dark; The cuckoo requires 1 lux to awaken, the black-headed warbler - 4, the chaffinch - 12, the house sparrow - 20 lux. In accordance with this, when the weather is good, birds in a given area wake up at a certain time and in a certain order, which suggests the existence of a “bird clock”. For example, in the forestry farm "Forest on Vorskla" of the Belgorod region in May-June, the first voices of birds are heard on average at the following times: nightingale - at 2 hours 31 minutes, blackbirds and songbirds - 2 hours 31 minutes, cuckoo - 3 hours 00 minutes, black-headed warbler - 3 hours 30 minutes, great tit - 3 hours 36 minutes, tree sparrow - 3 hours 50 minutes.
Daily changes in light conditions have a profound impact on the life of plants, and above all on the rhythm and intensity of photosynthesis, which stops in the dark hours of the day, in bad weather and in winter (Fig. 13).
Finally, solar energy can play a very important role as a source of heat, affecting living things directly or profoundly affecting their environment on a local or global scale.
In general, from the above fragmentary information it is clear that the light factor plays an extremely important and versatile role in the life of organisms.
Rice. 13. Dependence of photosynthesis on light energy in different plant populations (after: Odum, 1975).
1 - trees in the forest; 2 - leaves illuminated by the sun; 3 - shaded leaves.
A significant part of solar radiation reaching the Earth covers the wave range within 0.15 - 4.0 mmk. The amount of solar energy arriving at the Earth's surface at right angles is called the solar constant. It is equal to 1.4·10-3 J (m2/s).
Most of the radiation in the visible region of the spectrum reaches the earth's surface, 30
% - infrared and long-wave ultraviolet. The Earth's surface reaches:
Infrared rays (f - 3·10v11 Hz, - 3·10v12, λ from 710 - 3000 nm) – 45% (IR-
radiation is 50% of the Sun's radiation).
Visible rays (3 10v12 – 7.5 10v 16, λ 400 – 710 nm) – 48%
Ultraviolet rays (7.5 10v 16-10v17, λ 400-10 nm) -7%.
A small portion of solar radiation escapes back into the atmosphere. The amount of reflected radiation depends on the reflectivity (albedo) of the surface. Thus, snow can reflect 80% of solar radiation, so it heats up slowly. A grassy surface reflects 20%, and dark soils only 10 5 of incoming radiation.
Most of the solar energy absorbed by soil and reservoirs is spent on water evaporation. When water condenses, heat is released, which warms the atmosphere. Heating of the atmosphere also occurs due to the absorption of 20-25% of solar radiation.
Infrared radiation.
Infrared radiation (IR radiation) is electromagnetic radiation invisible to the human eye. The optical properties of matter in IR radiation differ significantly from those in the visible spectrum. For example, a layer of water of several cm is impenetrable to IR radiation with λ >1 μm.
About 20% of the infrared radiation of the solar spectrum is absorbed by dust, carbon dioxide and water vapor in the 10-kilometer layer of the atmosphere adjacent to the Earth's surface. In this case, the absorbed energy is converted into heat.
IR radiation makes up most of the radiation from incandescent lamps (unbearable heat when filming in sound stages) and gas-discharge lamps. IR radiation is emitted by ruby lasers.
The long-wave part of infrared radiation (> 1.4 µm) is retained mainly by the superficial layers of the skin, causing a burning sensation (heat rays). The medium- and short-wave part of IR rays and the red part of optical radiation penetrate to a depth of 3 cm. With large amounts of energy, they can cause overripening. Sunstroke is the result of local overheating of the brain.
Visible radiation is light.
Approximately half of the radiation comes from waves with wavelengths between 0.38 and 0.87 mmk. This is the spectrum visible to the human eye and perceived as light.
One of the visible aspects of the impact of radiant energy is illumination. It is known that light heals the environment (including its bactericidal effect). Half of the sun's total thermal energy is contained in the optical part of the solar radiant energy. Light is necessary for the normal functioning of physiological processes.
Effect on the body:
Stimulates vital activity;
Strengthens metabolism;
Improves overall well-being;
Improves mood;
Increases performance.
Lack of light:
Negative effect on the functions of the nerve analyzer (its fatigue increases):
Increased central nervous system fatigue;
Labor productivity decreases;
Occupational injuries are increasing;
Depressive states develop.
WITH Insufficient illumination is currently associated with a disease that has several names:“autumn-winter depression”, “emotional seasonal illness”, “seasonal affective disorder” (SAD). The lower the natural illumination of the area, the more common this disorder occurs. According to statistics, 5-10% of people have signs of this symptom complex (75% are women).
Darkness leads to the synthesis of melatonin, which in healthy people regulates the timing of nighttime sleep cycles so that it is healing and promotes long life. However, if melatonin production does not stop in the morning due to the influence of light on the pineal gland, lethargy and depression develop during the day due to inappropriately high daytime levels of this hormone.
Signs of SAD:
Signs of depression;
Difficulty waking up;
Decreased productivity at work;
Reduced social contacts;
Increased need for carbohydrates;
Weight gain.
There may be a decrease in the activity of the immune system, which is manifested by an increase in susceptibility to infectious (viral and bacterial) diseases.
These signs disappear in spring and summer, when the length of daylight increases significantly.
Autumn-winter depression is currently treated with light. Light therapy with an intensity of 10,000 lux in the morning gives a good effect. This is approximately 20 times higher than normal indoor illumination. The choice of duration of therapy is individual for each person. Most often, the procedure lasts 15 minutes. During this time, you can do any activity (read, eat, clean the apartment, etc.). A positive effect is observed within a few days. All symptoms completely stop after a few weeks. Side effects may include headaches.
The effect of treatment is associated with the regulation of the activity of the pineal gland, which modulates the production of melatonin and serotonin. Melatonin is responsible for falling asleep, and serotonin is responsible for waking up.
Also shown:
Psychotherapy;
Antidepressants.
IN At the same time, another type of disturbance of biological rhythms associated with modern lifestyle may currently be observed. Prolonged artificial light leads to a decrease in the inhibitory effect of melatonin on the activity of the gonads. This helps speed up puberty.
Ultraviolet (UV) radiation
Ultraviolet radiation belongs to the short-wave part of the solar spectrum. On the one hand, it borders on the softest part of ionizing radiation (X-rays), and on the other, on the visible part of the spectrum. Makes up 9% of all energy emitted by the Sun. At the boundary with the atmosphere, 5% of natural sunlight is absorbed; 1% reaches the Earth's surface.
Ultraviolet radiation from the Sun ionizes the gases in the upper layers of the Earth's atmosphere, which leads to the formation of the ionosphere. Short UV rays are blocked by a layer of ozone at an altitude of about 200 km. Therefore, only rays of 400-290 nm reach the earth's surface. Ozone holes allow the short-wavelength part of the UV spectrum to penetrate.
The intensity of action depends on:
Geographic location (latitude);
Time of day,
Weather conditions.
The biological properties of UV radiation depend on the wavelength. There are 3 ranges of UV radiation:
1. Region A (400-320 nm) - fluorescent, tanning. This is long-wave radiation, which is the dominant part. It is practically not absorbed in the atmosphere, therefore it reaches the Earth's surface. It is also emitted by special lamps used in solariums.
Action:
Causes the glow of some substances (luminophores, some vitamins);
Weak general stimulating effect;
Conversion of tyrosine into melanin (protection of the body from excess UV radiation).
The conversion of tyrosine to melanin occurs in melanocytes. These cells are located in the basal layer of the epidermis. Melanocytes are pigment cells of neuroectodermal origin. They are distributed unevenly throughout the body. For example, in the skin of the forehead there are 3 times more of them than in the upper limbs. Pale people and dark-skinned people contain the same number of pigment cells, but the content of melanin in them is different. Melanocytes contain the enzyme tyrosinase, which is involved in the conversion of tyrosine to melanin.
2. Region B (320 – 280 nm) – mid-wave, tanning UV radiation. A significant part of this range is absorbed by stratospheric ozone.
Action:
Improving physical and mental performance;
Increased nonspecific immunity;
Increasing the body's resistance to the action of infectious, toxic, carcinogenic agents.
Strengthening tissue regeneration;
Increased growth.
This is due to the stimulation of amino acids (tyrosine, tryptophan, phenylalanine, etc.), pririmidine and purine bases (thymine, cytosine, etc.). This leads to the breakdown of protein molecules (photolysis) with the formation of biologically active substances (choline, acetylcholine, histamine, etc.). BAS activate metabolic and trophic processes.
3. Region C (280 – 200 nm) – short-wave, bactericidal radiation. It is actively absorbed by the ozone layer of the atmosphere.
Action:
Vitamin D synthesis;
Bactericidal action.
Other types of UV radiation, as well as visible radiation, have a bactericidal effect, although less pronounced.
N!B! Mid- and short-wave UV rays in high doses can cause changes in nucleic acids and lead to cellular mutations. At the same time, long-wave radiation promotes the restoration of nucleic acids.
4. Region D (315 – 265 nm) is also distinguished, which has a pronounced antirachi-
tic action.
It has been shown that to satisfy the daily requirement for vitamin D, about 60 minimum erythemal doses (MED) are needed on exposed areas of the body (face, neck, arms). To do this, you need to stay in sunlight every day for 15 minutes.
Lack of UV radiation leads to:
Rickets;
Reducing general resistance;
Metabolic disorders (including osteoporosis?).
Excess UV radiation leads to:
Increased need of the body for essential amino acids, vitamins, Ca salts, etc.;
Inactivation of vitamin D (translation of cholecalceferol into indifferent and toxic substances);
The formation of peroxide compounds and epoxy substances, which can cause chromosomal aberrations, mutagenic and carcinogenic effects.
Exacerbation of some chronic diseases (tuberculosis, gastrointestinal tract, rheumatism, glomerulonephritis, etc.);
Development of photophthalmia (photoconjunctivitis and photokeratitis) 2–14 hours after irradiation. The development of photophthalmia can be as a result of the action of: A - direct sunlight, B - scattered and reflected light (snow, sand in the desert), C
– when working with artificial sources;
Dimerization of the protein crystallin (crystallin), which induces the development of cataracts;
There is an increased risk of retinal damage in individuals with a removed lens (even area A).
In persons with fermentopathy to dermatitis;
Development of malignant skin tumors (melanoma, basal cell carcinoma, squamous cell carcinoma),
Immunosuppression (changes in the ratio of lymphocyte subpopulations, a decrease in the number of Langerhans cells in the skin and a decrease in their functional activity) → a decrease in resistance to infectious diseases,
Accelerated skin aging.
Natural protection of the body from ultraviolet radiation:
1. The formation of tanning associated with the appearance of melanin, which:
capable of absorbing photons and thus weakening the effect of radiation;
is a trap for free radicals formed during skin irradiation.
2. Keratization of the upper layer of skin followed by peeling.
3. Formation of the trans-cis form of urocanic (urocaic) acid. This compound is capable of capturing UV radiation quanta. It is excreted in human sweat. In the dark, a reverse reaction occurs with the release of heat.
The criterion for skin sensitivity to UV radiation is the tanning burn threshold. It is characterized by the time of initial exposure to UV radiation (that is, before the formation of pigmentation), after which error-free DNA repair is possible.
IN middle latitudes are distinguished 4 skin types:
5. Particularly sensitive fair skin. It turns red quickly and doesn't tan well. Individuals are distinguished by blue or green eyes, the presence of freckles, and sometimes red hair. Tanning burn threshold – 5-10 minutes.
6. Sensitive skin. People of this type have blue, green or gray eyes, light brown or brown hair. The burn threshold for tanning is 10-20 minutes.
7. Normal skin (20-30 min.). People with gray or light brown eyes, dark brown or brown hair.
8. Insensitive skin(30-45 min.). Individuals with dark eyes, dark skin and dark hair color.
Modification of skin photosensitivity is possible. Substances that increase the skin's sensitivity to light are called photosensitizers.
Photosensitizers: aspirin, brufen, indocid, librium, bactrim, lasix, penicillin, plant furanocoumarins (celery).
Risk groups for developing skin tumors:
light, slightly pigmented skin,
sunburn received before the age of 15 years,
the presence of a large number of birthmarks,
the presence of birthmarks more than 1.5 cm in diameter.
Although ultraviolet irradiation is of primary importance in the development of malignant neoplasms,
skin, a significant risk factor is contact with carcinogenic substances -
mi, such as nickel contained in atmospheric dust and its mobile forms in the soil.
Protection against excessive UV exposure:
1. It is necessary to limit the time spent under intense sunlight, especially in the period of 10.00 - 14.00 hours, the peak for UVR activity. The shorter the shadow, the more destructive the UVR activity.
2. Sunglasses (glass or plastic with UV protection) should be worn.
3. Application of photoprotectors.
4. Application of sunscreens.
5. A diet high in essential amino acids, vitamins, macro- and microelements (primarily nutrients with antioxidant activity).
6. Regular examination by a dermatologist for people at risk of developing skin cancer. Signals for immediate contact with a doctor are the appearance of new
dark spots, loss of clear boundaries, changing pigmentation, itching and bleeding.
It must be remembered that UV radiation is intensely reflected from sand, snow, ice, concrete, which can increase the intensity of UV exposure by 10-50%. It should be remembered that UVR, especially UVA, affects humans even on cloudy days.
Photoprotectors are substances with a protective effect against damaging UV radiation. The protective effect is associated with the absorption or dissipation of photon energy.
Photoprotectors;
Para-aminobenzoic acid and its esters;
Melanin obtained from natural sources (such as mushrooms). Photoprotectors are added to sunscreens and lotions.
Sunscreens.
There are 2 types - with a physical effect and with a chemical effect. The cream should be applied 15-30 minutes before sunbathing, and again every 2 subsequent hours.
Physical sunscreens contain compounds such as titanium dioxide, zinc oxide and talc. Their presence leads to the reflection of UVA and UVB rays.
Sunscreens with a chemical effect include products containing 2-5% benzophenone or its derivatives (oxybenzone, benzophenone-3). These compounds absorb UVR and as a result break into 2 parts, which leads to the absorption of UVR energy. A side effect is the formation of two free radical fragments, which can damage cells.
Sunscreen SPF-15 filters out about 94% of UVR, SPF-30 blocks 97% of UVR, mainly UVB. UVA filtration in chemical sunscreens is low, accounting for 10% of UVB absorption.
Radiation. Radiant energy has a serious effect on microorganisms. Sunlight promotes the vital activity of a group of phototrophic microbes, in which biochemical reactions occur under the influence of solar energy. Most microorganisms are photophobic, that is, afraid of light. Direct sunlight has a detrimental effect on microbes, as evidenced by Buchner's experience. It consists of inoculating a bacterial culture onto an agar plate, placing pieces of dark paper on the bottom of the cup, and shining the cup with direct sunlight for 1-2 hours from the bottom, after which it is incubated. Bacterial growth is observed only in areas corresponding to the pieces of paper. The destructive effect of sunlight is primarily associated with exposure to ultraviolet radiation with a wavelength of 234 - 300 nm, which is absorbed by DNA and causes dimerization of thymine. This action of ultraviolet rays is used to neutralize air in various rooms, hospitals, operating rooms, wards, etc.
Ionizing radiation also has a detrimental effect on microorganisms, but microbes are highly resistant to this factor and are radioresistant (their death occurs when irradiated in doses of 10,000 - 100,000 R). This is associated with the small size of the target due to the low content of nucleic acids in microorganisms. Ionizing radiation is used to sterilize some biologically active substances and food products. The advantage of this method is that during such processing the properties of the processed object do not change.
Drying is one of the factors regulating the content of microorganisms in the external environment. The attitude of microbes to this effect depends largely on the conditions in which it occurs. Under natural conditions, drying has a detrimental effect on vegetative forms of bacteria, but has virtually no effect on spores, which can persist in a dried state for decades. During the drying process, vegetative cells lose free water and denaturation of cytoplasmic proteins occurs. However, many bacteria, especially pathogenic ones, can be well preserved in a dried state, being in pathological material, for example, in sputum, which forms something like a case around the bacterial cells.
When dried from a frozen state in a vacuum, microorganisms retain their viability well, which is associated with the transition to a state of suspended animation. This method of freeze-drying is widely used to preserve museum cultures of microorganisms.
Pressure. Microorganisms are resistant to high atmospheric pressure, due to which they are able to exist and develop at great depths - up to 10,000 m. Microorganisms tolerate high hydrostatic pressure well - up to 5,000 atm.
Ultrasound. When microorganisms are treated with ultrasound, cell death is observed due to their disintegration. It is believed that under the influence of ultrasound, cavitation cavities are formed in the cell, in which high pressure is created, which leads to the destruction of cell structures.
The effects of different forms of radiant energy on microorganisms manifest themselves in different ways. The action is based on certain chemical or physical changes occurring in the cells of microorganisms and in the environment.
The effect of radiant energy obeys the general laws of photochemistry - changes can only be caused by absorbed rays. Consequently, the penetrating ability of the rays is of great importance for the effectiveness of irradiation.
Light. In nature, microorganisms are constantly exposed to solar radiation. Light is necessary for the life of only photosynthetic microbes, which use light energy in the process of assimilation of carbon dioxide. Microorganisms that are not capable of photosynthesis grow well in the dark. Direct sunlight is harmful to microorganisms; even scattered light suppresses their growth to one degree or another. However, the development of many molds in the dark proceeds abnormally: in the constant absence of light, only the mycelium develops well, and sporulation is inhibited.
Pathogenic bacteria (with rare exceptions) are less resistant to light than saprophytic bacteria.
It is known that radiant energy is transferred in “portions” - quanta. The effect of a quantum depends on the energy content in it. The amount of energy varies depending on the wavelength: the longer it is, the lower the energy of the quantum.
Infrared rays (IR rays) have a relatively long wavelength. The energy of these radiations is not sufficient to cause photochemical changes in the substances that absorb them. Basically, it turns into heat, which has a detrimental effect on microorganisms when using IR radiation for heat treatment of products.
Ultra-violet rays. These rays are the most active part of the solar spectrum, causing its bactericidal effect. They have high energy, enough
precise in order to cause photochemical changes in the molecules of the substrate and cell that absorb them.
Rays with a wavelength of 250–260 nm have the greatest bactericidal effect.
The effectiveness of exposure to UV rays on microorganisms depends on the radiation dose, i.e., on the amount of energy absorbed. In addition, the nature of the irradiated substrate matters: its pH, the degree of contamination with microbes, as well as temperature.
Very small doses of radiation even have a stimulating effect on individual functions of microorganisms. Higher ones
but doses that do not lead to death cause inhibition of individual metabolic processes, change the properties of microorganisms, up to hereditary changes. This is used in practice to obtain variants of microorganisms with a high ability to produce antibiotics, enzymes and other biologically active substances. A further increase in the dose" leads to death. At a dose ■ below the lethal dose, restoration (reactivation) of normal life is possible.
Different microorganisms are not equally sensitive to the same dose of radiation (Fig. 24, 25).
Among nonsporeless bacteria, pigment bacteria are especially sensitive to irradiation; they secrete pigment in the surrounding area.
living environment. Pigment bacteria containing carotenoid pigments are extremely persistent, since carotenoid pigments have protective properties against UV rays.
Bacterial spores are much more resistant to UV rays than vegetative cells. It takes 4–5 times more energy to kill spores (see Table 9). Fungal spores are more resilient than mycelium.
The death of microorganisms can be a consequence of both the direct effect of UV rays on cells and unfavorable changes in the irradiated substrate for them.
UV rays inactivate enzymes, they are adsorbed by essential substances
cells (proteins, nucleic acids) and cause changes - damage to their molecules. Substances (hydrogen peroxide, ozone, etc.) that have a detrimental effect on microorganisms can be formed in the irradiated environment.
Currently, UV rays are widely used in practice. An artificial source of ultraviolet radiation is often low-pressure argon-mercury lamps, called bactericidal lamps (BUV-15,
Ultraviolet rays are used to disinfect the air in refrigeration chambers, medical and industrial premises. Treatment with UV rays for 6 hours destroys up to 80% of bacteria and molds in the air. Such rays can be used to prevent infection from the outside during bottling, packaging and packaging of food products, medicinal preparations, as well as for the disinfection of containers, packaging materials, equipment, and utensils (in public catering establishments).
Recently, the bactericidal properties of UV rays have been successfully used to disinfect drinking water.
Sterilization of food products using UV rays is hampered by their low penetrating ability, and therefore the effect of these rays appears only on the surface or in a very thin layer. However, it is known that irradiation of chilled meat and meat products extends their shelf life at 2–3 times.
