The evolution of breath.

1) Diffuse breathing is the process of equalizing the concentration of oxygen inside the body and in its environment. Oxygen penetrates through the cell membrane in unicellular organisms.

2) Skin respiration- this is the exchange of gases through the skin in lower worms, in vertebrates (fish, amphibians), which have special respiratory organs.

gill breathing

PIRATE GILLS(skin outgrowths on both sides of the body) appear in marine annelids, aquatic arthropods, and mollusks in the mantle cavity.

GILLS- respiratory organs of vertebrates, formed as an invagination of the digestive tube.

In the lancelet, gill slits pierce the pharynx and open into the peribranchial cavity with frequent changes of water.

Fish have gills made from gill arches with gill filaments pierced by capillaries. The water swallowed by the fish enters the oral cavity, passes through the gill filaments to the outside, washes them and supplies the blood with oxygen.

4) Tracheal and pulmonary breathing- more efficient, since oxygen is absorbed immediately from the air, and not from the water. It is typical for terrestrial mollusks (sac-like lungs), arachnids, insects, amphibians, reptiles, birds, mammals.

arachnids have lung sacs (scorpions), tracheas (ticks), and spiders have both.

INSECTS have tracheas - the respiratory organs of terrestrial arthropods - a system of air tubes that open with breathing holes (stigmas) on the lateral surfaces of the chest and abdomen.

AMPHIBIANS have 2/3 cutaneous respiration and 1/3 pulmonary. Airways appear for the first time: larynx, trachea, bronchial rudiments; light - smooth-walled bags.

REPTILES have developed airways; the lungs are cellular, there is no skin respiration.

BIRDS have developed airways, light spongy. Part of the bronchi branches outside the lungs and forms - air sacs.

Air bags- air cavities connected to the respiratory system, 10 times the volume of the lungs, which serve to enhance air exchange in flight, do not perform the function of gas exchange. Breathing at rest is carried out by changing the volume of the chest.

Breathing in flight

1. When the wings are raised, air is sucked through the nostrils into the lungs and posterior air sacs (in the lungs I gas exchange);

Anterior air sacs ← light - posterior air sacs

2. When the wings are lowered, the air sacs are compressed, and air from the rear air sacs enters the lungs (in the lungs II gas exchange).

Front air bags - ← light rear air bags

double breath is the exchange of gases in the lungs during inhalation and exhalation.

MAMMALS- gas exchange almost entirely in the lungs (through the skin and alimentary canal -2%)

airways: nasal cavity → nasopharynx → pharynx → larynx → trachea → bronchi (bronchi branch into bronchioles, alveolar ducts and end with alveoli - pulmonary vesicles). The lungs are spongy and consist of alveoli surrounded by capillaries. The respiratory surface is increased by 50-100 times compared to the body surface. The type of breathing is alveolar. The diaphragm that separates the chest cavity from the abdominal cavity, as well as the intercostal muscles, provide ventilation to the lungs. Complete separation of the oral and nasal cavities. Mammals can breathe and chew at the same time.

The gill apparatus in chordates evolved towards the formation of gill filaments. In particular, fish have developed 4-7 gill sacs, which are gaps between the gill arches and contain a large number of petals, which are penetrated by capillaries (Fig. 190). In fish, an air bladder also participates in respiration.[ ...]

Gill respiration is a typical aquatic respiration. The physiological purpose of the gills is to supply the body with oxygen. They transfer oxygen from the external environment to the blood.[ ...]

Skin respiration, as the most primary in phylogenesis and ontogenesis, is then replaced by a special, gill respiration, but still continues to play a certain role until the end of the life of the fish.[ ...]

Respiratory system. The gills are the organs of respiration. They lie on both sides of the head. They are based on gill arches. In the vast majority of cases, in our freshwater fishes, with the exception of lampreys only, the gills are covered on the outside with covers, and their cavity communicates with the oral cavity. On the gill arches there are two-row gill plates. Each gill plate is oblong, pointed, tongue-shaped, has a cartilaginous stamen at its base, enclosed in a bone cap and reaching to its free end. Along the inner edge of the gill plate runs a branch of the branchial artery, which brings venous blood, and along the outer edge - a branch of the branchial vein, which drains arterial blood. Hair vessels depart from them. On both flat sides of the gill plate are leaf-like plates, which actually serve for respiration or gas exchange. If there is only one row of plates on the gill arch, then it is called a semi-gill.[ ...]

In gobies, breathing in moist air is provided by the scalp, oral and gill cavities. The mucous membrane of these cavities is well supplied with blood vessels. Air is taken in by the mouth, oxygen is taken up in the mouth or gill cavity, and the remaining gas is expelled back through the mouth. Interestingly, many gobies do not have a swim bladder, and other organs are adapted for air breathing.[ ...]

In a number of fish, gill respiration in the early stages of development does not fully satisfy the needs of the organism. As a result, additional organs develop (subintestinal, superior tail and dorsal veins), which serve as a significant addition to gill breathing. With the development and improvement of gill respiration, embryonic respiration is gradually reduced.[ ...]

In addition to the frequency of respiration, changes are also observed in the depth of respiration. Fish in some cases (with low P02, elevated temperature, high CO2 content in the water) breathe very often. The respiratory movements themselves are small. Such shallow breathing is especially easy to observe at elevated temperatures. In some cases, the fish takes a deep breath. Mouth and gill covers open and close wide. With shallow breathing, the respiratory rhythm is large, with deep breathing it is small.[ ...]

Observing the rhythm of fish breathing, M. M. Voskoboinikov came to the conclusion that the passage of water in one direction through the mouth, gill filaments and gill openings is ensured by the work of the gill covers and the special position of the gill filaments.[ ...]

As the gill type of breathing develops, salmon use oxygen more easily, even if the latter is in a low concentration (decrease in the threshold concentration of O2).[ ...]

The ratio of main respiration to additional respiration varies in different fish. Even in the loach, intestinal respiration has changed from supplementary to almost equal to gill respiration. Vyun still needs. intestinal respiration, even if it is in well-aerated water. From time to time, it rises to the surface and swallows air, and then sinks to the bottom again. If, for example, in a perch or carp, with a lack of oxygen, the respiratory rhythm quickens, then the loach in. under such conditions, it does not speed up the rhythm of breathing, but uses intestinal respiration more intensively.[ ...]

Water is pumped through the gill cavity by the movement of the mouthparts and gill covers. Therefore, the respiratory rate in fish is determined by the number of movements of the gill covers. The breathing rhythm of fish is primarily affected by the oxygen content in the water, as well as the concentration of carbon dioxide, temperature, pH, etc. Moreover, the sensitivity of fish to a lack of oxygen (in water and blood) is much higher than to an excess of carbon dioxide (hypercapnia) . For example, at 10 ° C and a normal oxygen content (4.0-5.0 mg / l), trout performs 60-70, carp - 30-40 respiratory movements per minute, and at 1.2 mg 02 / l, the respiratory rate increases 2-3 times. In winter, the carp's breathing rhythm slows down sharply (up to 3-4 breaths per minute).[ ...]

With the mouth open and the gill covers closed, the zoda enters the oral cavity, passes between the gill filaments into the gill cavity. This is a breath. Then the mouth closes, and the operculum opens slightly and the water comes out. This is exhalation. Consideration of this process in detail led to two different ideas about the mechanism of respiration.[ ...]

In some fish, the pharynx and gill cavity are adapted for air breathing.[ ...]

Gills are the main respiratory organ in most fish. However, examples can be given where in some fish the role of gill respiration is reduced, while the role of other organs in the process of respiration is increased. Therefore, it is not always possible to answer the question of what the fish breathes at the moment. Significantly expanding the Bethe table, we present the relations different forms respiration in fish under normal conditions (Table 85).[ ...]

The inhibitory effect of excess CO2 on gill respiration and the stimulation of pulmonary respiration in lungfish have been repeatedly noted. The transition of lungfish from water to air breathing is accompanied by a decrease in arterial p02 and an increase in pCO2. It should be especially noted that the stimulation of air respiration and the suppression of water respiration in lungfish occurs under the influence of a decrease in the level of 02 in the water and an increase in the level of CO2. True, under hypoxia in lungfish ((Cheosegagoskk) both pulmonary and gill respiration intensifies, and under hypercapnia, only pulmonary respiration. It is curious that under the combined action of hypoxia and hypercapnia, ventilation of the lungs increases, and the gills decrease. in the region of the gills or in the efferent gill vessels.[ ...]

The underdevelopment or complete absence of the gill cover makes it difficult to breathe and leads to disease of the gills. The slanting snout interferes with food intake. The arched back and pug-shaped head lead to a significant stunting.[ ...]

The most common type of intestinal respiration is that in which air is driven through the intestines and gas exchange occurs in the middle or back part of it (loaches, some catfishes). In another type, such as Hippostomos and Acarys, the air, after being in the intestines for some time, does not exit through the anus, but is squeezed back into the oral cavity and then thrown out through the gill slits. This type of intestinal breathing is fundamentally different from the first; subsequently, in some fish, it developed into pulmonary respiration.[ ...]

A more complex adaptation for air breathing is the supra-gill organ. The nadzhaberny organ is available in Opy-ocephalus (snakehead), living in the river. Cupid, in Luciocephalus, in Anabas, etc. This organ is formed by a protrusion of the pharynx, and not the gill cavity proper, as in labyrinth fish.[ ...]

Respiratory movements, respiratory rhythm. In fish, the gill cover periodically opens and closes. These rhythmic movements of the operculum have long been known as respiratory movements. However, a correct understanding of the breathing process has been achieved relatively recently.[ ...]

It is quite obvious that the intensity of skin respiration is an expression of the adaptability of fish to life in conditions of oxygen deficiency, when gill respiration is not able to provide the body with oxygen in the required amount.[ ...]

Observed general rule: with the development of air respiration, there is a decrease in the gill (Suvorov). Anatomically, this is expressed in the shortening of the gill filaments (in Polypterus, Ophiocephalus, Arapaima, Electrophorus) or in the disappearance of a number of lobes (in Monopterus, Amphipnous and lungfish). In protopterus, for example, petals are almost completely absent on the first and second arches, while in lepidosiren, gill filaments are poorly developed.[ ...]

The fish of warm waters have a device for air breathing in the form of a labyrinth. The labyrinth organ is formed by a protrusion of the gill cavity proper and is sometimes (as in Anatas) supplied with its own musculature. The inner surface of the “labyrinth cavity” has a variety of curvatures due to curved bone plates covered with a mucous membrane. Many blood vessels and capillaries approach the surface of the "labyrinth cavity". Blood enters them from a branch of the fourth afferent branchial artery. Oxygenated blood flows into the dorsal aorta. The air captured by the fish in the mouth enters the labyrinth from the oral cavity and gives oxygen to the blood there.[ ...]

More recently, S. V. Streltsova (1949) has carried out more detailed studies of skin respiration in 15 species of fish. It determined both general respiration and specifically skin respiration. Gill respiration was turned off by applying a hermetic rubber mask to the gills. This technique allowed her to determine the share of skin respiration in the total respiration of fish. It turned out that this value is very different for different fish and is associated with the way of life and ecology of fish.[ ...]

Experiments have shown that the V, VII, IX and X pairs of head nerves are necessary for normal breathing. Branches from them innervate the upper jaw (V pair), gill cover (VII pair) and gills (IX and X pairs).[ ...]

In practice, all cyclostomes and fish have a "morphofunctional reserve" for increasing the power of respiration in the form of some "higher" gas exchange structures. It has been experimentally established that no more than 60% of the gill filaments function in fish under normal conditions. The rest are switched on only in conditions of impending hypoxia or with an increase in oxygen demand, for example, with an increase in swimming speed.[ ...]

In the larval stage (tadpoles), amphibians are very similar to fish: they retain gill breathing, have fins, a two-chambered heart, and one circle of blood circulation. Adult forms are characterized by a three-chambered heart, two circles of blood circulation, two pairs of limbs. The lungs appear, but they are poorly developed, so additional gas exchange occurs through the skin (Fig. 81). Amphibians live in warm, humid places, and are especially common in the tropics, where they are most numerous.[ ...]

Sturgeon larvae and fry are transported in the first two days after hatching from eggs before switching to gill breathing, since gill breathing requires more oxygen. Saturation of water with oxygen should be at least 30% of normal saturation. At a water temperature of 14-17 ° C and constant aeration, the planting density, depending on the mass of larvae, can be increased to 200 pcs. per 1 liter of water.[ ...]

At the age of 15 days, the larva has enlarged axillary veins that encircle the intestines (already performing the function of respiration), and a pectoral fin with densely branched vessels. At the age of 57 days, the external gills of the larva have shrunk and are completely covered by the gill cover. Everything. fins, except preanal, well supplied with vessels. These fins serve as respiratory organs (ri £.-67).[ ...]

In a carefully performed test on the same species of fish - on brook trout, it was shown that already at pH 5.2, hypertrophy of the mucous cells of the gill epithelium occurs, and mucus accumulates on the gills. Subsequently, with an increase in water acidity to 3.5, destruction of the gill epithelium and its rejection from supporting cells was noted. The accumulation of mucus on the gills during the period when breathing is especially difficult has also been noted in other salmon species.[ ...]

It is necessary to increase the pO2 at which HbO2 is formed. For the most part, gill breathing and heart rate increase in fish. In this case, not only the maintenance of p02 at a higher level occurs, but also a decrease in pCO2. However, the body can only achieve this within certain temperature limits, since the water in the reservoir is less oxygenated at elevated temperatures than at low temperatures. IN laboratory conditions and when transporting live fish in closed vessels, the condition of the fish can be improved by this; that with an increase in temperature, the RH in the water is increased artificially, by aeration.[ ...]

The supragillary and labyrinth organs are found in the snakehead and in tropical fish (cockerel, gourami, macropods). They are sac-like protrusions of the gill cavity (labyrinth organ) or pharynx (supra-gill organ) and are intended mainly for air breathing.[ ...]

In the European bitterling, the vessels of the respiratory network reach greater development than our other cyprinids. This is the result of the adaptation of the organism to life in the gill cavity of mollusks in the early stages of development under poor oxygen conditions. With the transition to life in water, all these adaptations disappear and only developed gill breathing remains.[ ...]

Fish are divided into cartilaginous and bony. The habitat of fish is water bodies, which shaped the features of their body and created fins as organs of movement. Breathing is gill, and the heart is two-chambered and one circle of blood circulation.[ ...]

According to R. Lloyd, the leading moment in this case is an increase in the flow of water passing through the gills, and, as a result, an increase in the amount of poison reaching the surface of the gill epithelium with subsequent penetration into the body. Moreover, the concentration of poison on the surface of the gill epithelium is determined not only by the concentration of the poison in the bulk of the solution, but also by the rate of respiration. We add to this that according to the data obtained by M. Shepard, with a decrease in the concentration of oxygen in the water, the content of hemoglobin in the blood increases and, most importantly, the rate of blood circulation through the gills increases.[ ...]

By the way, the same ability was used to explain the cases of Kgrp life with overgrown mouths. And here, studies have shown that these carps drag out their existence for some time, having adapted to take in water for breathing and, along with it, a certain number of crustaceans through the gill openings.[ ...]

Chordates are also characterized by the presence of a nerve bundle in the form of a tube above the notochord and a digestive tube under the notochord. Further, they are characterized by the presence in the embryonic state or throughout life of numerous gill slits that open outward from the pharyngeal region of the digestive tube and are respiratory organs. Finally, they are characterized by the location of the heart or its replacement vessel on the ventral side.[ ...]

Summarizing the numerous experimental data available today on the effect of long-term or short-term oxygen deficiency on fish of various ecologies, a number of general conclusions can be drawn. The primary reaction of fish to hypoxia is an increase in respiration by increasing its frequency or depth. The volume of gill ventilation at the same time increases sharply. The heart rate drops, the stroke volume of the heart increases, as a result of which the volume of blood flow remains constant. During the development of hypoxia, oxygen consumption initially increases slightly, then returns to normal. As hypoxia deepens, the efficiency of oxygen absorption begins to decrease, while oxygen consumption by tissues increases, which creates additional difficulties for fish in providing oxygen demand under conditions of its low content in water. Oxygen tension in arterial and venous blood, utilization of oxygen from water, the efficiency of its transfer and the efficiency of blood oxygenation are reduced.[ ...]

The recording of the electrocardiogram is carried out as follows. Electrodes soldered onto thin flexible conductors are inserted: one into the region of the heart on the ventral side of the body, and the other - between the dorsal fin and the head on the dorsal side. To record the respiratory rate, electrodes are inserted into the operculum and into the rostrum. Respiratory rate and heart rate can be recorded simultaneously through two independent channels of an electrocardiograph or any other device (for example, a two-channel electroencephalograph). In this case, the fish can be both in a free state in an aquarium, and in a fixed one. Recording an electrocardiogram is feasible only in conditions of complete screening of the aquarium water. Screening can be done in two ways: by immersing a plate of galvanized iron in water or by soldering a conductor to the bottom of the aquarium. If the aquarium is plexiglass, it should be installed on a sheet of iron.[ ...]

Comparing these data for juveniles with those of Kuptsis for adult roach, it is easy to see that the threshold value in juvenile roach on the 49th day after hatching is very close to the threshold value for the adult (1 and 0.6-1 mg/l, respectively). Consequently, after the establishment of gill respiration, the ability to use oxygen quickly reaches its limit.[ ...]

The gills play an important role in removing excess salts. If divalent ions are excreted in significant quantities through the kidneys and the digestive tract, then monovalent ions (mainly Na and CG) are excreted almost exclusively through the gills, which in fish perform a dual function - respiration and excretion. In the gill epithelium there are special large goblet cells containing a large number of mitochondria and a well-developed eudoplasmic reticulum. These "chloride" (or "salt") cells are located in the primary gill filaments and, unlike the respiratory cells, are associated with the vessels of the venous system. The transfer of ions through the gill epithelium has the character of active transport and proceeds with the expenditure of energy. The stimulus for the excretory activity of chloride cells is an increase in blood osmolarity.[ ...]

Suspended solids tend to form unstable or stable suspensions and include both inorganic and organic components. With an increase in their content, light transmission deteriorates, photosynthesis activity decreases, and appearance water and gill respiration may be disturbed. As solid particles settle to the bottom, the activity of benthic flora and fauna decreases.[ ...]

In the ontogenesis of fish, a certain sequence of the role of individual oxygen-receiving surfaces is observed: the stellate sturgeon egg breathes the entire surface; in the embryo, oxygen supply occurs mainly through a dense network of capillaries on the yolk sac; after hatching, approximately on the 5th day, gill breathing appears, which then becomes the main one.[ ...]

The loach rises to the surface of the water to swallow air at: t = 10 ° 2-3 times per hour, and at 25-30 ° already 19 times. If the water is boiled, i.e., P02 is reduced, then the loach rises to the surface at t \u003d 25-2.7 ° 'once an hour. At t=5° in running water, it did not rise to the surface for 8 hours. These experiments show quite clearly that intestinal respiration, which is a supplement to gill respiration, copes quite satisfactorily with its function at low demands of the organism at 02 (at t = 5°) or at a high concentration of oxygen in the environment (running water). But gill respiration is not enough if the metabolism in the body is increased (t == 25-30°) or if the P02 in the medium (boiled water) is greatly reduced. In this case, intestinal respiration is additionally switched on, and the loach receives the required amount of oxygen.[ ...]

In the Devonian, the climate was sharply continental, arid, with sharp temperature fluctuations during the day and seasons, extensive deserts and semi-deserts appeared. The first glaciations were also observed. During this period, fish flourished, inhabiting the seas and fresh water. At that time, many surface water bodies dried up in summer period, froze through, and the fish that inhabited them could be saved in two ways: burrowing into the silt or migrating in search of water. Lungfish took the first path, in which, along with gill breathing, pulmonary respiration developed (the lung developed from the swim bladder). Their fins looked like blades, consisting of individual bones with muscles attached to them. With the help of fins, fish could crawl along the bottom. In addition, they too could have pulmonary respiration. The lobe-finned fish gave rise to the first amphibians - stegocephals. On land in the Devonian, the first forests of giant ferns, horsetails and club mosses appear.[ ...]

Of the general clinical changes in fish, the following are noted: depression of the general condition, suppression and perversion of reactions to: external stimuli; darkening, pallor, hyperemia and hemorrhages on the skin of the body; ruffling of scales; violation of the sense of balance, orientation, coordination of movements and coordinated work of the fins; conjunctivitis, keratitis, cataracts, corneal ulceration, bulging eyes, loss of vision; complete or partial refusal to take food; swelling of the abdomen (acute cases of poisoning); change in the rhythm of breathing and the amplitude of oscillation of the gill covers; periodic cramps of the muscles of the body, tremor of the gill covers and pectoral fins. With chronic intoxication, signs of increasing exhaustion develop. In severe processes develops: toxic dropsy. In case of death, poisoned fish: from the surface of the water sink to the bottom, they develop a coma, breathing becomes shallow, then stops - death occurs.[ ...]

Less clear is the localization of peripheral receptors that perceive changes in CO2 content and the pathways for conducting impulses from these receptors to the respiratory center. So, for example, after transection of the IX and X pairs of cranial nerves innervating the gills, the impulses remained in a weakened form. In lung-breathing fish, gill respiration is noted to be inhibited with an increase in pCO2 in the water, which can be relieved by atropine. The effect of pulmonary respiration suppression under the influence of excess carbon dioxide was not observed in these fish, which gives grounds to assume the presence of CO2-sensitive receptors in the gill region.

The set of processes that ensure the consumption of O 2 and the release of CO 2 in the body is called breath. There are processes of external and internal respiration. External respiration ensures the exchange of gases between the body and the external environment, internal respiration - the consumption of O2 and the release of CO 2 by the cells of the body.

The factor that ensures the diffusion of gases through the respiratory surfaces is the difference in their concentrations. The movement of dissolved gases occurs in the direction from the area with their high concentration to the area of ​​low concentration.

In small organisms, gas exchange, as a rule, is carried out diffusely over the entire surface of the body (or cell). In larger animals, gases are transported to the tissues either directly (tracheal system of insects) or with the help of special vehicles (blood, hemolymph).

The amount of oxygen entering the tissues of the animal depends on the area of ​​the respiratory surface and the difference in oxygen concentration on them. Therefore, in all respiratory organs there is an increase in the respiratory epithelium. To maintain a high gradient of oxygen diffusion on the exchange membrane, the movement of the medium (ventilation) is necessary. It is provided by the respiratory rhythmic movements of the entire body of the animal (small bristle worm tubifex, leeches) or certain parts of it (crustaceans), as well as the work of the ciliary epithelium (molluscs, lancelet).

A number of fairly large animals do not have specialized respiratory organs. In them, gas exchange is carried out through moist skin, equipped with an abundant network of blood vessels (earthworm). Cutaneous respiration as an additional characteristic of animals with specialized respiratory organs. For example, in eels with gills, 60% of the oxygen demand is provided by skin respiration, in frogs with lungs, this value is more than 50%.

The respiratory organs in aquatic environment are the gills, in the ground-air - the lungs and trachea.

Gills are organs located outside the body cavity in the form of epithelial surfaces penetrated by a dense network of blood capillaries. Gill breathing is characteristic of polychaete annelids, most molluscs, crustaceans, fish, and amphibian larvae. Gill respiration is most effective in fish. It is based on backflow phenomenon: blood in the capillaries of the gill filaments flows in the opposite direction to the current of the ox washing the gills.

Lungs, as a rule, are internal organs and are protected from drying out. There are two types of them: diffusion And ventilation. In the lungs of the first type, gas exchange is carried out only by diffusion. Relatively small animals have such lungs: lung mollusks, scorpions, spiders. Only terrestrial vertebrates have ventilatory lungs.

The complication of the structure of the lungs in the series from amphibians to mammals is associated with an increase in the area of ​​the respiratory epithelium. So, in amphibians, 1 cm 3 of lung tissue has a total gas exchange surface of 20 cm 2. The same indicator for human lung epithelium is 300 cm 2 .

Simultaneously with an increase in the respiratory surface, the mechanism of lung ventilation improves, which, starting with reptiles, is carried out by changing the volume of the chest, and in mammals, with the participation of the muscles of the diaphragm. These adaptations allowed warm-blooded animals (birds and mammals) to dramatically increase the intensity of their metabolism.

The third type of respiratory organs - trachea. They are air-filled thin-walled, branching, non-collapsing protrusions inside the body. The tracheae communicate with the external environment through openings in the cuticle - spiracles. In insects, they most often have 12 pairs: 3 pairs on the chest and 9 pairs on the abdomen. The spiracles can close or open depending on the amount of oxygen. At high degree development of the tracheal system (in insects), its numerous branches braid all the internal organs and directly provide gas exchange in tissues. The fundamental difference between tracheal respiration and pulmonary and gill respiration is that it does not require the participation of blood as a transport mediator in gas exchange.

The tracheal system is able to maintain a sufficiently high level of tissue respiration, thereby providing a high physiological activity of the insect.

Ventilation of the trachea in insects in the absence of flight is carried out most often by rhythmic contractions of the abdomen; during flight, it is enhanced by movements of the chest.

Aquatic larvae of some insects breathe with the help of tracheal gills. In this case, the tracheal system is devoid of spiracles, i.e. it is closed and filled with air. The branches of the closed tracheal system go into the "gills" - appendages with a large surface and a thin cuticle that allows gas exchange between water and air of the tracheal system. Such tracheal gills are present, for example, in mayfly larvae. In the larvae of some dragonflies, the tracheal gills are located in the cavity of the rectum, and the insect ventilates them by taking water into the intestine and pushing it back.

Gas exchange, or respiration, is expressed in the absorption of oxygen from the body environment(water or atmosphere) and release in the last carbon dioxide as the end product of the oxidative process occurring in the tissues, due to which the energy necessary for life is released. Oxygen is taken up by the body in a variety of ways; they can basically be characterized as: 1) diffuse breathing and 2) local breathing, that is, by special organs.

diffuse breathing consists in the absorption of oxygen and the release of carbon dioxide by the entire surface of the outer cover - skin respiration - and n and e - and the epithelial membrane of the digestive tube - to and sh ch n about e respiration, i.e. without organs specially adapted for this purpose. A similar method of gas exchange is characteristic of some types of primitive multicellular animals, such as sponges, coelenterates and flatworms, and is due to their lack of a circulatory system.

It goes without saying that diffuse respiration is inherent only in organisms in which the volume of the body is small, and its surface is relatively extensive, since it is known that the volume of the body increases in proportion to the cube of the radius, and the corresponding surface - only to the square of the radius. Therefore, with a large volume of the body, this method of breathing is insufficient.

However, even with more or less appropriate volume-to-surface ratios, diffuse respiration still cannot always satisfy organisms, since the more vigorously vital activity is manifested, the more intense the oxidative processes in the body should proceed.

With intensive manifestations of life, despite the small volume of the body, it is necessary to increase its area of ​​​​contact with the environment containing oxygen, and special devices to accelerate the ventilation of the respiratory tract. An increase in the area of ​​gas exchange is achieved by the development of special respiratory organs.

Special respiratory organs vary considerably in details of construction and location in the body. For aquatic animals, such organs are the gills, for terrestrial animals, the traxae and invertebrates, and for vertebrates, the lungs.

Gill breathing. Gills are external and internal. Primitive external gills represent a simple protrusion of villous offspring of the skin, abundantly supplied with capillary vessels. Such gills in some cases differ little in their function from diffuse respiration, being only its higher stage (Fig. 332- A, 2). Usually they are concentrated in the front parts of the body.

The internal gills are formed from the folds of the mucous membrane of the initial section of the digestive tube between the gill slits (Fig. 246-2-5; 332- 7). The skin adjacent to them forms abundant branching in the form of petals with a large number of capillary blood vessels. The internal gills are often covered by a special fold of skin (gill cover), oscillatory movements which improve the conditions of exchange, increasing the flow of water and removing its used portions.

Internal gills are characteristic of aquatic vertebrates, and the act of gas exchange in them is complicated by the passage of portions of water to the gill slits through the oral cavity and the movements of the gill cover. In addition, their gills are included in the circulatory circle. Each gill arch has its own vessels, and thus, at the same time, a higher differentiation of the circulatory system is carried out.

Of course, with gill methods of gas exchange, skin respiration can also be preserved, but so weak that it is relegated to the background.

In describing the oropharynx of the digestive tract, it has already been said that the gill apparatus is also characteristic of some invertebrates, such as, for example, hemichordates and chordates.

Lung breathing- a very perfect way of gas exchange, easily serving the organisms of massive animals. It is characteristic of terrestrial vertebrates: amphibians (not in the larval state), reptiles, birds and mammals. A number of organs with other functions join the act of gas exchange concentrated in the lungs, as a result of which the pulmonary method of breathing requires the development of a very complex complex of organs.

When comparing aquatic and terrestrial types of respiration in vertebrates, one important anatomical difference should be kept in mind. During gill respiration, portions of water enter the primitive mouth one by one and are released through the gill slits, where oxygen is extracted from it by the vessels of the gill folds. Thus, the gill breathing apparatus of vertebrates is characterized by an inlet and a number of outlets. During pulmonary respiration, the same openings are used for the introduction and removal of air. This feature, of course, is associated with the need to take in and push out portions of air for faster ventilation of the gas exchange area, i.e., with the need to expand and contract the lungs.

It can be assumed that the distant, more primitive ancestors of vertebrates had independent muscle tissue in the walls of the swim bladder transforming into light; with its periodic contractions, air was pushed out of the bladder, and as a result of its expansion, fresh portions of air were collected due to the elasticity of the bladder walls. Elastic tissue, along with cartilage, now dominates as a support in the respiratory system.

In the future, with an increase in the vital activity of organisms, such a mechanism of respiratory movements became already imperfect. In the history of development, it was replaced by force concentrated either in the oral cavity and the anterior part of the trachea (amphibians), or in the walls of the chest and abdominal cavities (reptiles, mammals) in the form of a specially differentiated part of the trunk muscles (respiratory muscles) and, finally, diaphragm. The lung obeys the movements of this musculature, expanding and contracting passively, and retains the elasticity necessary for this, as well as a small muscular apparatus as an auxiliary device.

Skin respiration becomes so insignificant that its role is reduced almost to zero.

Gas exchange in the lungs in terrestrial vertebrates, as well as in aquatic ones, is closely connected with the circulatory system through the organization of a separate, respiratory, or small, circle of blood circulation.

It is quite clear that the main structural changes in the body during pulmonary respiration come down to: 1) an increase in the contact of the working area of ​​the lungs with air, and 2) a very close and no less extensive connection of this area with the thin-walled capillaries of the circulatory circle.

The function of the respiratory apparatus - to pass air into its many channels for gas exchange - speaks for the nature of its construction in the form of an open, gaping system of tubes. Their walls, in comparison with the soft intestinal tube, are composed of a harder support material; sometimes in the form of bone tissue (nasal cavity), and mainly in the form cartilage tissue and easily pliable, but quickly returning to normal elastic tissue.

The mucous membrane of the respiratory tract is lined with a special ciliated epithelium. Only in a few areas does it change into a different form in accordance with other functions of these areas, such as, for example, in the olfactory region and in the places of gas exchange itself.

Throughout the pulmonary respiratory tract, three peculiar areas attract attention. Of these, the initial - n axial strip with t - serves for the perceived air, examined here for smell. The second section - the throat - is a device for isolating the respiratory tract from the digestive tract during the passage of the food coma through the pharynx, for making sounds and, finally, for producing cough shocks that eject mucus from the respiratory tract. The last section, lёg to and e-represent the organ of direct gas exchange.

Between the nasal cavity and the larynx is the cavity of the pharynx, common with the digestive apparatus, and between the larynx and the lung, the respiratory

throat, or trachea. Thus, the passing air is used by the described expanding sections in three different directions: a) perceived odors, b) devices for making sounds and, finally, in) gas exchange, of which the latter is the main one.

Table 19 Comparative characteristics structures of larvae and adult frogs
sign	Larva (tadpole)	adult animal
body shape	Fish-like, with rudiments of limbs, tail with a swimming membrane	The body is shortened, two pairs of limbs are developed, there is no tail
Way to travel	Swimming with the tail	Jumping, swimming with the help of the hind limbs
Breath	Gills (gills first external, then internal)	Pulmonary and skin
Circulatory system	Two-chambered heart, one circle of blood circulation	Three-chambered heart, two circles of blood circulation
sense organs	The organs of the lateral line are developed, there are no eyelids in front of the eyes	There are no lateral line organs, eyelids are developed in front of the eyes
Jaws and way of eating	Horny plates of the jaws scrape off algae along with unicellular and other small animals	There are no horny plates on the jaws, with a sticky tongue it captures insects, molluscs, worms, fish fry
Lifestyle	Water	Terrestrial, semi-aquatic

Reproduction. Amphibians have separate sexes. The sex organs are paired, consisting of slightly yellowish testes in the male and pigmented ovaries in the female. The efferent ducts extend from the testes, penetrating into the anterior part of the kidney. Here they connect with the urinary tubules and open into the ureter, which simultaneously performs the function of the vas deferens and opens into the cloaca. The eggs from the ovaries fall into the body cavity, from where they are brought out through the oviducts, which open into the cloaca.

In frogs, sexual diformism is well expressed. So, the male has tubercles on the inner toe of the forelegs ("marriage callus"), which serve to hold the female during fertilization, and vocal sacs (resonators) that amplify the sound when croaking. It should be emphasized that the voice first appears in amphibians. Obviously, this is related to life on land.

Frogs breed in the spring in their third year of life. Females spawn eggs into the water, males irrigate it with seminal fluid. Fertilized eggs develop within 7-15 days. Tadpoles - frog larvae - differ greatly in structure from adult animals (Table 19). After two or three months, the tadpole turns into a frog.