Class Amphibians = Amphibians.

The first terrestrial vertebrates that still retained a connection with the aquatic environment. The class includes 3900 species and includes 3 orders: tailed (salamanders, newts), legless (tropical worms) and tailless (toads, tree frogs, frogs, etc.).

Secondary aquatic animals. Since there is no amniotic cavity in the egg (together with cyclostomes and amphibians, they are referred to as anamnias), they reproduce in water, where they pass through the initial stages of their development. At different stages of the life cycle, amphibians lead a terrestrial or semi-aquatic lifestyle, are distributed almost everywhere, mainly in areas with high humidity along the shores of fresh water bodies and on damp soils. Among amphibians, there are no forms that could live in salty sea water. Various modes of movement are characteristic: species are known that make rather long jumps, move with a step or "crawl", devoid of limbs (worms).

The main signs of amphibians.

    Amphibians have retained many of the features of their purely aquatic ancestors, but along with this they acquired a number of features characteristic of real terrestrial vertebrates.

    For tailed and tailless larval development with gill breathing in fresh water (frog tadpoles) and their metamorphosis into an adult, breathing with the lungs, are characteristic. In legless, upon hatching, the larva takes the form of an adult animal.

    The circulatory system is characterized by two circles of blood circulation. The heart is three-chambered. It has one ventricle and two atria.

    The cervical and sacral parts of the spine are separated, each having one vertebra.

    Adult amphibians are characterized by paired limbs with articulated joints. The limbs are five-fingered.

    The skull with two occipital condyles is movably articulated with the cervical vertebra.

    The pelvic girdle is tightly attached to the transverse processes of the sacral vertebra.

    The eyes have movable eyelids and blinking membranes to keep the eyes from clogging and drying out. Due to the convex cornea and the flattened lens, accommodation is improved.

    The forebrain enlarges and divides into two hemispheres. The midbrain and cerebellum are insignificantly developed. 10 pairs of cranial nerves depart from the brain.

    The skin is bare, i.e. devoid of any horn or bone formations, permeable to water and gases. Therefore, it is always moist - oxygen first dissolves in the liquid covering the skin, and then diffuses into the blood. The same thing happens with carbon dioxide, but in the opposite direction.

    Kidneys, like in fish, primary = mesonephric.

    To catch the sound waves of the air, the tympanic membrane appears, behind it is the middle ear (tympanic cavity), in which the auditory ossicle is located - the stirrup, which conducts vibrations to the inner ear. The eustachian tube connects the middle ear cavity with the oral cavity. Choans appear - internal nostrils, the nasal passages become through.

    The body temperature is unstable (poikilothermia) depends on the ambient temperature and only slightly exceeds the latter.

Aromorphoses:

    Lungs and pulmonary respiration appeared.

    The circulatory system has become more complex, the pulmonary circulation has developed, i.e. amphibians have two circles of blood circulation - large and small. The heart is three-chambered.

    Paired five-fingered limbs were formed, representing a system of levers with hinged joints and intended for movement on land.

    A cervical spine was formed in the spine, which ensures the movement of the head, and the sacral region is the place of attachment of the pelvic girdle.

    The middle ear, eyelids, and choana appeared.

    Muscle differentiation.

    Progressive development of the nervous system.

Phylogeny.

Amphibians evolved from ancient cross-finned fish in the Devonian period of the Paleozoic era about 350 million years ago. The first amphibians - ichthyostegs - in appearance resembled modern tailed amphibians. Their structure had features characteristic of fish, including the rudiments of the operculum and organs of the lateral line.

Cover. Two-layer. The epidermis is multilayered, the corium is thin, but abundantly supplied with capillaries. Amphibians retained the ability to produce mucus, but not by individual cells, like in most fish, but by mucous glands of the alveolar type. In addition, amphibians often have granular glands with poisonous secretions of varying degrees of toxicity. The skin color of amphibians depends on special cells - chromatophores. These include melanophores, lipophores and iridocytes.

Under the skin, frogs have extensive lymphatic lacunae - reservoirs filled with tissue fluid and allowing the accumulation of water under adverse conditions.

Skeleton subdivided into axial and additional, as in all vertebrates. The vertebral column is more differentiated into sections than in fish and consists of four sections: cervical, trunk, sacral and caudal. The cervical and sacral regions each have one vertebra. There are usually seven trunk vertebrae in tailless, and all caudal vertebrae (about 12) merge into a single bone - the urostyle. The caudate has 13 - 62 trunk and 22 - 36 caudal vertebrae; in legless people the total number of vertebrae reaches 200 - 300. The presence of a cervical vertebra is important because unlike fish, amphibians cannot turn their body so quickly, and the cervical vertebra makes the head mobile, but with a small amplitude. Amphibians cannot turn their head, but they can tilt it.

The vertebrae in different amphibians can differ in their type. In legless and lower tailed vertebrae, the vertebrae are amphiticel, with a preserved chord, like in fish. In the higher caudate, the vertebrae are opisthocoelous, i.e. the bodies are curved in front and concave in the back. In tailless, on the contrary, the anterior surface of the vertebral bodies is concave, and the posterior surface is curved. These vertebrae are called procellus. The presence of articulated surfaces and articulated processes provides not only a strong connection of the vertebrae, but also makes the axial skeleton mobile, which is important for the movement of caudate amphibians in water without the participation of limbs, due to lateral bends of the body. In addition, vertical movements are possible.

The skull of amphibians is, as it were, a modified skull of a bony fish, adapted for terrestrial existence. The cerebral skull remains predominantly cartilaginous for life. The occipital region of the skull contains only two lateral occipital bones, which are carried along the articular condyle, with which the skull is attached to the vertebrae. The visceral skull of amphibians undergoes the greatest transformations: secondary upper jaws appear; formed by the intermaxillary (premaxillary) and maxillary bones. Reduction of gill respiration led to a radical change in the hyoid arch. The hyoid arch is transformed into a hearing aid element and a hyoid plate. Unlike fish, the visceral skull of amphibians is directly attached by palatal-square cartilage to the bottom of the cerebral skull. This type of direct connection of the components of the skull without the participation of the elements of the hyoid arch is called autostyle. Elements of the operculum are absent in amphibians.

The accessory skeleton includes the bones of the girdles and free limbs. As in fish, the bones of the amphibian shoulder girdle are located in the thickness of the muscles that connect them to the axial skeleton, but the girdle itself is not directly connected to the axial skeleton. The belt provides support for the free limb.

All land animals constantly have to overcome the force of gravity, which is not necessary for fish. The free limb serves as a support, allows the body to be raised above the surface and provides movement. Free limbs consist of three sections: proximal (one bone), intermediate (two bones), and distal (relatively large number of bones). In representatives of different classes of terrestrial vertebrates, there are structural features of one or another free limb, but all of them are of a secondary nature.

In all amphibians, the proximal part of the free forelimb is represented by the humerus, the intermediate part is represented by the ulna and radius in the caudates and the single forearm bone (formed as a result of the fusion of the ulna and radius) in tailless. The distal region is formed by the wrist, metacarpus and phalanges of the fingers.

The hind limb girdle articulates directly with the axial skeleton, with its sacral region. Reliable and rigid connection of the pelvic girdle with the spinal column ensures the work of the hind limbs, which are more important for the movement of amphibians.

Muscular system differs from the muscular system of fish. The trunk musculature retains its metameric structure only in legless individuals. In caudates, metamerism of the segments is disrupted, and in tailless amphibians, sections of muscle segments begin to separate, differentiating into ribbon-like muscles. The mass of the musculature of the limbs increases sharply. In fish, the movements of the fins are provided mainly by the muscles located on the trunk, while the five-toed limb moves due to the muscles located in it. A complex system of muscles - antagonists - flexor and extensor muscles appears. Segmented musculature is present only in the region of the spinal column. The muscles of the oral cavity (chewing, tongue, floor of the mouth) become more complex and specialized, not only participating in the seizure and swallowing of food, but also providing ventilation of the oral cavity and lungs.

Body cavity- the whole. In amphibians, due to the disappearance of the gills, the relative position of the pericardial cavity has changed. She was pushed to the bottom of the chest into the area covered by the sternum (or coracoid). Lungs lie above it in a pair of coelomic canals. Cavities containing the heart and lungs. Separated by the pleurocardial membrane. The cavity in which the lungs are located communicates with the main coelom.

Nervous system. The brain is of the ichthyopid type, i.e. the main integrating center is the midbrain, but the brain of amphibians has a number of progressive changes. The brain of amphibians has five divisions and differs from the brain of fish, mainly in the greater development of the forebrain, the complete division of its hemispheres. In addition, the nerve substance already lines, in addition to the bottom of the lateral ventricles, also the sides and roof, forming the cerebral vault - the archipallium. The development of the archipallium, accompanied by increased connections with the diencephalon and especially the midbrain, leads to the fact that associative activity that regulates behavior is carried out in amphibians not only by the medulla oblongata and midbrain, but also by the hemispheres of the forebrain. The elongated hemispheres in front have a common olfactory lobe, from which two olfactory nerves originate. Behind the forebrain is the diencephalon. The pineal gland is located on its roof. There is a crossover of the optic nerves (chiasm) on the underside of the brain. From the bottom of the diencephalon, the funnel and the pituitary gland (lower cerebral gland) depart.

The midbrain is presented in the form of two circular visual lobes. An underdeveloped cerebellum lies behind the visual lobes. Immediately behind it is the medulla oblongata with a rhomboid fossa (fourth ventricle). The medulla oblongata gradually passes into the spinal cord.

In amphibians, 10 pairs of brain nerves depart from the brain. The eleventh pair is undeveloped, while the twelfth pair extends outside the skull.

There are 10 pairs of true spinal nerves in a frog. The three front ones take part in the formation of the brachial plexus, which innervates the front limbs, and the four rear pairs - in the formation of the lumbosacral plexus, which innervates the hind limbs.

Sense organs provide orientation of amphibians in water and on land.

    Lateral line organs are present in all larvae and in adults with an aquatic lifestyle. They are represented by an accumulation of sensitive cells with nerves suitable for them, which are scattered throughout the body. Sensitive cells perceive temperature, pain, tactile sensations, as well as changes in humidity and chemical composition of the environment.

    The organs of smell. Amphibians have a small outer nostril on each side of the head that leads into an elongated sac that ends in an inner nostril (choana). Joanas open at the front of the roof of the mouth. In front of the choanas, to the left and to the right, there is a sac, which open into the nasal cavity. This is the so-called. vomeronasal organ. It contains a large number of sensory cells. Its function is to obtain olfactory information about food.

    The organs of vision have a structure characteristic of a terrestrial vertebrate. This is expressed in the convex shape of the cornea, the lens in the form of a biconvex lens, in the movable eyelids, which protect the eyes from drying out. But accommodation, like in fish, is achieved by moving the lens by contracting the ciliary muscle. The muscle is located in the annular ridge surrounding the lens, and when it contracts, the lens of the frog moves forward a little.

    The organ of hearing is arranged according to the terrestrial type. The second section appears - the middle ear, in which the auditory ossicle, which first appears in vertebrates, is placed - the stirrup. The tympanic cavity is connected to the pharyngeal region by the Eustachian tube.

The behavior of amphibians is very primitive, conditioned reflexes are developed slowly and fade away quickly. The motor specialization of reflexes is very small; therefore, the frog cannot form a protective reflex of withdrawing one paw, and when one limb is irritated, it jerks with both paws.

Digestive system begins with the mouth opening leading into the oropharyngeal cavity. It contains a muscular tongue. The ducts of the salivary glands open into it. The tongue and salivary glands first appear in amphibians. The glands serve only to wet the food lump and are not involved in the chemical processing of food. On the intermaxillary, maxillary bones, vomer, simple conical teeth are located, which are attached to the bone with the base. The digestive tube differentiates into the oropharyngeal cavity, a short esophagus that carries food into the stomach, and a bulky stomach. The pyloric part passes into the duodenum - the beginning of the small intestine. The pancreas lies in the loop between the stomach and the duodenum. The small intestine smoothly passes into the large intestine, which ends with a pronounced rectum that opens into the cloaca.

The digestive glands are the liver with the gallbladder and the pancreas. The liver ducts, together with the gallbladder duct, open into the duodenum. The pancreatic ducts flow into the gallbladder duct, i.e. this gland does not have an independent communication with the intestine.

That. The digestive system of amphibians differs from the analogous system of fish in the greater length of the digestive tract, the final section of the large intestine opens into the cloaca.

Circulatory system closed. Two circles of blood circulation. The heart is three-chambered. In addition, there is a venous sinus in the heart, which communicates with the right atrium, and the arterial cone departs on the right side of the ventricle. Three pairs of vessels, homologous to the gill arteries of fish, branch off from it. Each vessel begins with an independent opening. All three vessels of the left and right sides go first by a common arterial trunk, surrounded by a common membrane, and then branch out.

The vessels of the first pair (counting from the head), homologous to the vessels of the first pair of gill arteries in fish, are called the carotid arteries, which carry blood to the head. Through the vessels of the second pair (homologous to the second pair of fish branchial arteries) - the aortic arches - the blood is directed to the back of the body. From the arches of the aorta, the subclavian arteries depart, carrying blood to the forelimbs.

Through the vessels of the third pair, homologous to the fourth pair of fish gill arteries - the pulmonary arteries - blood is directed to the lungs. From each pulmonary artery, there is a large cutaneous artery that directs blood to the skin for oxidation.

Venous blood from the anterior end of the body is collected through two pairs of jugular veins. The latter, merging with the cutaneous veins, which have already taken in the subclavian veins, forms two anterior vena cava. They carry mixed blood into the venous sinus, since arterial blood moves through the cutaneous veins.

Amphibian larvae have one circle of blood circulation, their circulatory system is similar to that of fish.

Amphibians have a new circulatory organ - the red bone marrow of the tubular bones. Erythrocytes are large, nuclear, leukocytes are not the same in appearance. There are lymphocytes.

The lymphatic system. In addition to the lymphatic sacs located under the skin, there are lymphatic vessels and hearts. One pair of lymphatic hearts is placed near the third vertebra, the other near the cloacal foramen. The spleen, which looks like a small round red body, is located on the peritoneum near the beginning of the rectum.

Respiratory system. It is fundamentally different from the respiratory system of fish. In adults, the respiratory organs are the lungs and skin. The airways are short due to the absence of the cervical spine. Represented by the nasal and oropharyngeal cavities, as well as the larynx. The larynx opens directly into the lungs with two openings. Due to the reduction of the ribs, the lungs are filled by swallowing air - according to the principle of a pressure pump.

Anatomically, the respiratory system of amphibians includes the oropharyngeal cavity (upper airways) and the laryngeal-tracheal cavity (lower tracts), which directly passes into the saccular lungs. The lung in the process of embryonic development is formed as a blind outgrowth of the anterior (pharyngeal) part of the digestive tube, therefore, in an adult state, it remains associated with the pharynx.

That. the respiratory system in terrestrial vertebrates is anatomically and functionally subdivided into two sections - the airway system and the respiratory section. The airways carry out two-way transport of air, but do not participate in the gas exchange itself, the respiratory section carries out gas exchange between the internal environment of the body (blood) and atmospheric air. Gas exchange occurs through the surface liquid and proceeds passively in accordance with the concentration gradient.

The operculum system becomes unnecessary, therefore the branchial apparatus in all terrestrial animals is partially modified, its skeletal structures are partially included in the skeleton (cartilage) of the larynx. Ventilation of the lungs is carried out due to the forced movements of special somatic muscles during the respiratory act.

Excretory system, as in fish, it is represented by primary, or trunk kidneys. These are compact bodies of reddish-brown color, lying on the sides of the spine, and not ribbon-like, like in fish. A thin Wolffian canal extends from each kidney to the cloaca. In female frogs, it serves only as a ureter, and in males, both as a ureter and vas deferens. In the cloaca, the wolf channels open with independent holes. It also opens separately into the cloaca and bladder. The final product of nitrogen metabolism in amphibians is urea. In aquatic amphibian larvae, the main product of nitrogen metabolism is ammonia, which is excreted in the form of a solution through the gills and skin.

Amphibians are hyperosmotic animals in relation to fresh water. As a result, water constantly enters the body through the skin, which has no mechanisms to prevent this, as in other terrestrial vertebrates. Sea water is hyperosmotic in relation to the osmotic pressure in the tissues of amphibians, when placed in such an environment, water will leave the body through the skin. That is why amphibians cannot live in seawater and die from dehydration in it.

The reproductive system. In males, the reproductive organs are represented by a pair of rounded whitish testes adjacent to the abdominal surface of the kidneys. Thin vas deferens extend from the testes to the kidneys. The reproductive products from the testis through these tubules are sent to the kidney bodies, then to the wolffian canals and along them into the cloaca. Before flowing into the cloaca, the Wolffian canals form a small expansion - seminal vesicles, which serve for temporary deposition of sperm.

The reproductive organs of females are represented by paired ovaries of a granular structure. Above them are fatty bodies. They accumulate nutrients that provide the formation of reproductive products during hibernation. In the lateral parts of the body cavity, there are strongly convoluted light oviducts, or Müllerian canals. Each oviduct opens into a body cavity in the region of the heart with a funnel; the lower uterine part of the oviducts is sharply expanded and opens into the cloaca. Ripe eggs fall out through the rupture of the walls of the ovary into the body cavity, then are captured by the funnels of the oviducts and move along them into the cloaca.

The wolffian canals in females perform only the functions of the ureters.

In tailless amphibians, fertilization is external. The eggs are immediately irrigated with semen.

External sexual characteristics of males:

    Males have a genital wart on the inner toe of the forelimbs, which reaches a special development at the time of reproduction and helps males to retain females during fertilization of eggs.

    Males are usually smaller than females.

Development amphibians are accompanied by metamorphosis. The eggs contain relatively little yolk (mesolecital eggs), so radial crushing occurs. A larva emerges from the egg - a tadpole, which in its organization is much closer to fish than to adult amphibians. It has a characteristic fish-like shape - a long tail surrounded by a well-developed swimming membrane, on the sides of the head it has two or three pairs of external cirrus gills, paired limbs are absent; there are lateral line organs, the pronephros (pronephros) is a functioning kidney. Soon the external gills disappear, and in their place three pairs of gill slits with their gill petals develop. At this time, the similarity between the tadpole and fish is also a two-chambered heart, one circle of blood circulation. Then, by protruding from the abdominal wall of the esophagus, paired lungs develop. At this stage of development, the arterial system of the tadpole is extremely similar to the arterial system of cross-fins and lungfishes, and the whole difference boils down to the fact that, due to the absence of the fourth gill, the fourth bringing branchial artery passes without interruption into the pulmonary artery. Still later, the gills are reduced. In front of the gill slits, a fold of skin is formed on each side, which, gradually expanding backward, tightens these slits. The tadpole goes over entirely to pulmonary respiration and swallows air through its mouth. In the future, paired limbs are formed in the tadpole - first the front, then the rear. However, the front ones are hidden longer under the skin. The tail and intestines begin to shorten, mesonephros appears, the larva gradually passes from plant food to animal food and turns into a young frog.

During the development of the larva, its internal systems are rebuilt: respiratory, circulatory, excretory, and digestive. Metamorphosis ends with the formation of a miniature copy of an adult.

For an ambist, a characteristic neoteny, i.e. they reproduce larvae, which for a long time were taken for an independent species, therefore they have their own name - axolotl. Such a larva is larger than an adult. Another interesting group is the water-dwelling proteas, which retain their external gills throughout their life, i.e. signs of a larva.

The metamorphosis of a tadpole into a frog is of great theoretical interest, since not only proves that amphibians evolved from fish-like creatures, but makes it possible to reconstruct in detail the evolution of individual organ systems, in particular the circulatory and respiratory systems, during the transition of aquatic animals to terrestrial ones.

Meaning amphibians consists in the fact that they eat many harmful invertebrates and themselves serve as food for other organisms in food chains.

Table 19. Comparative characteristics of the structure of larvae and adult frogs
Sign Larva (tadpole) Adult animal
Body shape Fish-like, with primordial limbs, tail with 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 hind limbs
Breath Gill (gills are first external, then internal) Pulmonary and cutaneous
Circulatory system Two-chambered heart, one circle of blood circulation Three-chambered heart, two circles of blood circulation
Sense organs The lateral line organs are developed, there are no eyelids in the eyes There are no lateral line organs, the eyelids are developed in the eyes
Jaws and way of eating Scrape off algae with the horny plates of the jaws together with unicellular and other small animals There are no horny plates on the jaws, with a sticky tongue it captures insects, mollusks, worms, fish fry
Lifestyle Water Terrestrial, semi-aquatic

Reproduction. Amphibians are dioecious. The genitals are paired, consisting of slightly yellowish testes in the male and pigmented ovaries in the female. Outflow ducts depart from the testes and penetrate into the anterior part of the kidney. Here they connect to the urinary tubules and open into the ureter, which simultaneously acts as the vas deferens and opens into the cloaca. Eggs from the ovaries fall into the body cavity, from where, through the oviducts, which open into the cloaca, they are taken out.

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

Frogs breed in the spring in the 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 to three months, the tadpole turns into a frog.

Breath of animals – set of processes that providehit into the body from the environmentoxygen , hisuse by cells for the oxidation of organic substances andexcretion from the body of carbon dioxide.Such breathing is calledaerobic , and organisms -aerobes .

OK. No. 28. Biology.

Green algae chlorella

Infusoria-shoe

The respiration process in animals is conventionally divided into three stages :

External respiration = gas exchange... Through this process, the animal receives oxygen and gets rid of carbon dioxide, which is the end product of metabolism.

Transport of gases in the body- this process is provided either by special tracheal tubes or internal body fluids (blood containing hemoglobin- a pigment that can attach oxygen and transport it to cells, as well as carry carbon dioxide out of cells).

Internal breathing- occurs in cells. Simple nutrients (amino acids, fatty acids, simple carbohydrates) are oxidized and broken down with the help of enzymes, during which the ENERGY necessary for the vital activity of the body is released.

The main role of respiration is to release energy from nutrients with the help of oxygen, which takes part in oxidation reactions.

Some of the simplest are - anaerobic organisms, i.e. organisms, oxygen-free. Anaerobes are optional and obligatory. Facultatively anaerobic organisms are organisms that can live in the absence of oxygen, or in its presence. Obligate anaerobic organisms are organisms for which oxygen is toxic. They can only live in the absence of oxygen. Anaerobic organisms do not need oxygen to oxidize nutrients.

Brachonella - anaerobic ciliate

Intestinal lamblia

Human roundworm

By way of breathing and the structure of the respiratory system in animals, 4 types of respiration are distinguished:

Cutaneous respiration Is the exchange of oxygen and carbon dioxide through the integument of the body. This process is based on the most important physical process - diffusion ... Gases enter only in a dissolved state through the integument shallowly and at a low speed. Such respiration in organisms that are small in size, wet integuments, lead an aquatic lifestyle. It - sponges, coelenterates, worms, amphibians.

Tracheal breathing –

carried out by

systems of connected

tubules - trachea , which

permeate the whole body, without

participation of liquids. WITH

their environment

connect special

holes - spiracles.

Organisms with tracheal

breathing is also small (no more than 2 cm, otherwise the body will not have enough oxygen). It - insects, centipedes, arachnids.

Gill breathing - with the help of specialized formations with a dense network of blood vessels. These outgrowths are called gills ... In aquatic animals - polychaete worms, crustaceans, molluscs, fish, certain amphibian species... In invertebrates, the gills are usually external, and in chordates, internal. Gill-breathing animals have additional forms of breathing through the skin, intestines, mouth surface, swim bladder.

Polychaete with gills

Crustacean gills

Nudibranch

Pulmonary respiration - this is breathing with the help of internal specialized organs - lungs.

Lungs– these are hollow thin-walled bags, entwined with a dense network of tiny blood vessels - capillaries. Diffusion of oxygen from the air into the capillaries occurs on the inner surface of the lungs. Accordingly, the larger this inner surface is, the more active diffusion is.

Almost all terrestrial vertebrates breathe lungs - reptiles, birds, some terrestrial invertebrates - spiders, scorpions, lung molluscs, and some aquatic animals - lungfish. Air enters the lungs through Airways.

Lungs of a mammal


Reptile lung

The respiratory system of birds

Respiration in animals is determined by their way of life and is carried out with the help of integuments, trachea, gills and lungs.

Respiratory system – a set of organs for carrying air or water, which contain oxygen, and gas exchange between the body and the environment.

Respiratory organs develop as outgrowths of the outer covers or walls of the intestinal tract. The respiratory system includes the respiratory tract and gas exchange organs. In vertebrates Airways – nasal cavity, larynx, trachea, bronchi ; a respiratory system -lungs .

Comparative characteristics of the respiratory system.

Group

Respiratory characteristics

Coelenterates

Gas exchange across the entire surface of the body. There are no special respiratory organs.

Ringed worms

External gills (polychaete worms) and the entire surface of the body (small bristle worms, leeches)

Molluscs

Gills (bivalves, cephalopods) and lungs (gastropods)

Arthropods

Gills (crustaceans), trachea and lungs (arachnids), trachea (insects)

Fishes

Gills. Additional respiratory organs: lungs (lungfish), areas of the mouth, pharynx, intestines, swim bladder

Amphibians

Cellular lungs, gills (in larvae), skin (with a large number of vessels). Respiratory tract: nostrils, mouth, tracheal-laryngeal chamber

Reptiles

Light honeycomb. Respiratory tract: nostrils, larynx, trachea, bronchi

Birds

The lungs are spongy. Respiratory tract: nostrils, nasal cavity, upper larynx, trachea, lower larynx with vocal apparatus, bronchi. There are air bags.

Mammals

Lungs are alveolar. Respiratory tract: nostrils, nasal cavity, larynx with vocal apparatus, trachea, bronchi.

Respiratory system functions:

    Delivery of oxygen to the cells of the body and removal of carbon dioxide from the cells of the body and gas exchange(main function).

    Regulation of body temperature(because water can evaporate through the surface of the lungs and respiratory tract)

    Purification and disinfection of incoming air(nasal mucus)

Questions for self-control.

Grade

Questions for self-control

1.What is breathing?

2. What are the main stages of breathing?

3. Name the main types of respiration in animals.

4. Give examples of animals that breathe with their skin, gills, trachea, and lungs.

5. What is the respiratory system?

6. What are the main functions of the respiratory system?

7. What is the importance of breathing for the release of energy in animal cells?

8. What determines the type of respiration of animals?

9. What functions does the respiratory system perform?

10. Describe the breathing methods of vertebrates.

Comparative characteristics of the respiratory organs of animals.

Respiratory system

Structural features

Functions

Examples of

Gills

External(comb, filamentous and feathery) or internal(always associated with the pharynx) thin-walled outgrowths of the body that contain many blood vessels

Gas exchange in the aquatic environment

In fish, almost all larvae of tailless amphibians, in most mollusks, some worms and arthropods

Trachea

Branched tubules that permeate the entire body and open outward with holes (stigmas)

Gas exchange in air

Most arthropods

Lungs

Thin-walled sacs that have a branched network of vessels

Gas exchange in air

In some molluscs and fish, terrestrial vertebrates

The branchial apparatus in chordates evolved in the direction of the formation of branchial lobes. In particular, fish have developed 4-7 gill sacs, which are gills between the gill arches and contain a large number of petals, which are penetrated by capillaries (Fig. 190). In fish, an air bubble is also involved in respiration. [...]

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

Cutaneous respiration, as the most primary in phylogeny and ontogeny, is then replaced by a special, branchial respiration, but nevertheless a well-known "role continues to play until the end of the fish's life. [...]

Respiratory system. The gills are the respiratory organs. They lie on either side of the head. They are based on the gill arches. In the vast majority of cases in our freshwater fish, with the exception of only lampreys, the gills are covered with lids on the outside, and their cavity communicates with the oral cavity. On the branchial arches there are two-row branchial plates. Each branchial plate is oblong, pointed, lingual in shape, has a cartilaginous stamen at its base, enclosed in a bony cap and reaching to its free end. A branch of the branchial artery, which carries venous blood, runs along the inner edge of the branchial plate, and a branch of the branchial vein, which carries arterial blood, runs along the outer edge. Hair vessels depart from them. On both flat sides of the branchial plate there are leaf-shaped plates, which actually serve for breathing or exchange of gases. If there is only one row of plates on the branchial arch, then that is called a semi-toad swarm. [...]

In gobies, breathing in humid air is provided by the scalp, mouth and gill cavity. The mucous membrane of these cavities is well supplied with blood vessels. Air is taken in by the mouth, oxygen is absorbed in the mouth or branchial cavity, and the remaining gas is thrown 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 respiration. With the development and improvement of gill respiration, embryonic respiration is gradually reduced. [...]

In addition to the respiration rate, changes are also observed in the depth of respiration. Fish in some cases (at low PO2, elevated temperature, high CO2 content in the water) breathes very often. The breathing movements themselves are small. This shallow breathing is especially easy at elevated temperatures. In some cases, the fish takes deep breaths. The mouth and operculums open and close wide. With shallow breathing, the respiratory rhythm is large, with deep breathing - small. [...]

Observing the rhythm of fish respiration, MM Voskoboinikov came to the conclusion that the passage of water in one direction through the mouth, gill lobes and gill openings is ensured by the operation of the gill covers and the special position of the gill lobes. [...]

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

The ratio of primary and secondary respiration varies in different fish. Even in the loach, intestinal respiration from additional has turned into almost equal to gill respiration. Loach still needs. intestinal respiration, even if it is in well-aerated water. From time to time, he rises to the surface and swallows air, and then again sinks to the bottom. If, for example, in a perch or carp with a lack of oxygen, the respiratory rhythm becomes more frequent, then the loach c. such conditions does not accelerate the rhythm of respiration, but more intensively uses intestinal respiration. [...]

Water is pumped through the gill cavity using the movement of the mouth apparatus and gill covers. Therefore, the respiration rate in fish is determined by the number of movements of the gill covers. The breathing rhythm of fish is primarily influenced 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 ° С and normal oxygen content (4.0-5.0 mg / l), trout makes 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 rhythm of carp breathing slows down sharply (up to 3-4 respiratory movements per minute). [...]

With an open mouth and closed gill covers, the zode enters the oral cavity, passes between the branchial lobes into the branchial cavity. This is a breath. Then the mouth closes, and the operculum opens slightly and water flows out. This is the exhalation. Consideration of this process in detail led to two different views on the mechanism of respiration. [...]

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

The gills are the main respiratory organ in most fish. However, examples can be cited when in some fish the role of gill respiration is reduced, while the role of other organs in the respiration process is increased. Therefore, it is not always possible to answer the question of what the fish is breathing at the moment. Having significantly expanded the Bethe table, we present the ratios of different forms of respiration in fish under normal conditions (Table 85). [...]

The inhibitory effect of excess CO2 on gill respiration and the stimulation of pulmonary respiration in lung breathing fish have been repeatedly noted. The transition of lung-breathing fish from water respiration to air respiration is accompanied by a decrease in arterial pO2 and an increase in pCO2. It should be especially noted that the stimulation of air respiration and inhibition of water respiration in lung-breathing fish occurs under the influence of a decrease in the level of 02 in the water and an increase in the level of CO2. True, with hypoxia in lungfish ((Cheosegagosk), both pulmonary and gill respiration are enhanced, and with hypercapnia, only pulmonary respiration. in the region of the gills or in the efferent gill vessels. [...]

The underdevelopment or complete absence of the operculum makes breathing difficult and leads to gill disease. The oblique snout interferes with food intake. An arched back and a pug-like head lead to significant growth retardation. [...]

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

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

Respiratory movements, respiratory rhythm. In fish, the operculum 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 was achieved relatively recently. [...]

It is quite obvious that the intensity of skin respiration is an expression of the fish's adaptability to life in conditions of oxygen deficiency, when gill respiration is unable to provide the body with oxygen in the required amount. [...]

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

Fish of warm waters have a device for air breathing in the form of a labyrinth. The labyrinth organ is formed by the protrusion of the branchial cavity proper and sometimes (like in Anabas), it is equipped with its own muscles. 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 is supplied to them from the branch of the fourth gill artery. The oxygenated blood flows into the dorsal aorta. The air captured by the fish in the mouth enters the labyrinth from the mouth and releases oxygen there into the blood [...]

More recently, S.V. Streltsova (1949) has carried out more detailed studies of cutaneous respiration in 15 species of fish. She determined both general respiration and especially skin respiration. Gill breathing was turned off by placing a sealed rubber mask over the gills. This technique allowed her to determine the share of the participation of skin respiration in the total respiration of fish. It turned out that this value is very different in different fish and is associated with the lifestyle and ecology of fish. [...]

Experiments have shown that V, VII, IX and X pairs of cranial nerves are necessary for normal respiration. The branches from them innervate the upper jaw (V pair), operculum (VII pair) and gills (IX and X pairs). [...]

Practically all cyclostomes and fish have a "morphofunctional reserve" for increasing the power of respiration in the form of some "swollen" gas exchange structures. It has been experimentally established that under normal conditions in fish no more than 60% of the gill petals function. The rest are turned on only under conditions of the onset of 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 respiration, have fins, a two-chambered heart and one circle of blood circulation. For adult forms, a three-chambered heart, two circles of blood circulation, two pairs of limbs are characteristic. Lungs appear, but they are poorly developed, so additional gas exchange occurs through the skin (Fig. 81). Amphibians live in warm, humid places, especially in the tropics, where they are most abundant. [...]

The larvae and fry of sturgeon fish are transported in the first two days after hatching from the eggs until the transition to gill respiration, since gill respiration requires more oxygen. The oxygen saturation of the water should be at least 30% of the normal saturation. At a water temperature of 14-17 ° C and constant aeration, the stocking density, depending on the mass of the larvae, can be increased to 200 pcs. for 1 liter of water. [...]

At the age of 15 days, the larva has enlarged subintestinal 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 in the larva, the external gills have contracted and are completely closed by the operculum. Everything. the fins, in addition to the preanal, are well supplied with vessels. These fins serve as respiratory organs (pic. -67). [...]

In a carefully performed test work 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 the acidity of the water to 3.5, the destruction of the branchial epithelium and its rejection from the supporting cells were noted. The accumulation of mucus on the gills during the period when breathing is especially difficult is also noted in other salmon species. [...]

It is necessary to increase pOr, at which HbO2 is formed. For the most part, gill respiration and heart rate increase in fish. In this case, there is not only maintenance of pO2 at a higher level, but also a decrease in pCOr. However, the organism can achieve this only within certain temperature limits, since the water in the reservoir is less saturated with oxygen 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; that with an increase in temperature, the PO in water is artificially increased by aeration. [...]

The supragill and labyrinth organs are found in the snakehead and in tropical fish (cockerels, gourami, macropods). They are saccular protrusions of the branchial cavity (labyrinth organ) or pharynx (supragillary organ) and are intended mainly for air breathing. [...]

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

Fish are subdivided into cartilaginous and bony. The habitat of fish is water bodies, which shaped the characteristics 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 is an increase in the flow of water passing through the gills, and, as a consequence, an increase in the amount of poison reaching the surface of the gill epithelium with subsequent penetration into the body. Moreover, the concentration of the poison on the surface of the branchial 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 oxygen concentration in water, the hemoglobin content in the blood increases and, which is especially important, the rate of blood circulation through the gills increases. [...]

Between n [ochim, the same ability was used to explain the incidents of life of the CCPs with an overgrown mouth. And here studies have shown that these carps drag out their existence for some time, having adapted to absorb water for breathing and 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 below the notochord. Further, they are characterized by the presence in the embryonic state or throughout their 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 the vessel replacing it 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 different ecology, a number of general conclusions can be drawn. The primary reaction of fish to hypoxia is an increase in respiration due to an increase in its frequency or depth. At the same time, the volume of gill ventilation 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. With the deepening of hypoxia, the efficiency of oxygen absorption begins to decrease, while oxygen consumption by tissues increases, which creates additional difficulties for fish in providing oxygen demand in conditions of its low content in water. The oxygen tension in arterial and venous blood, the utilization of oxygen from water, the efficiency of its transfer and the efficiency of blood oxygenation are reduced. [...]

An electrocardiogram is recorded 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. The respiratory rate and heart rate can be recorded simultaneously through two independent genals 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 the aquarium, and in a fixed one. The recording of an electrocardiogram is feasible only in conditions of complete screening of the aquarium water. Shielding can be done in two ways: by immersing galvanized iron plates in water or by soldering a conductor to the bottom of the aquarium. If the aquarium is plexiglass, it should be installed on an iron sheet. [...]

Comparing these data for juveniles with the data of Kuptsis for adult roach, it is easy to see that the threshold value for juvenile roach on the 49th day after hatching is very close to the threshold value for an 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 a significant role in the elimination of excess salts. If bivalent ions are excreted in significant quantities through the kidneys and the digestive tract, then monovalent ions (mainly Ni and SG) are excreted almost exclusively through the gills, which perform a double function in fish - respiration and excretion. The branchial epithelium contains 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 branchial lobes and, unlike the respiratory cells, are associated with the vessels of the venous system. The transfer of ions through the branchial epithelium has the character of active transport and goes 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, the transmission of light deteriorates, the activity of photosynthesis decreases, the appearance of water deteriorates and gill respiration may be disturbed. As the solids settle to the bottom, the activity of benthic flora and fauna decreases. [...]

In the ontogeny of fish, a definite sequence of the role of individual oxygen-receiving surfaces is observed: the stellate sturgeon egg breathes through the entire surface; in the embryo, the supply of oxygen occurs mainly through a dense network of capillaries on the yolk sac; after hatching, approximately on the 5th day, gill respiration 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, that is, to reduce PO2, then the loach rises to the surface at t = 25-2.7 ° 'once an hour. At t = 5 ° in running water, it did not rise to the surface for 8 hours. In these experiments, it was clearly shown that intestinal respiration, which is a complement to the branchial respiration, copes quite satisfactorily with its function at low body demands of 02 (at t = 5 °) or at a high oxygen concentration in the environment (running water). But gill respiration is not enough if the exchange in the body is increased (t == 25-30 °) or the PO2 in the environment (boiled water) has greatly decreased. 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 fluctuations in temperature during the day and according to the seasons; vast deserts and semi-deserts appeared. The first glaciations were also observed. During this period, fish flourished, inhabiting the seas and fresh waters. At that time, many terrestrial bodies of water dried up in the summer, froze through with a snake, and the fish inhabiting them could be saved by two ways: burrowing in silt or migrating in search of water. The first path was taken by lung breathing fish, which, along with the gill, developed pulmonary respiration (the lung developed from the swim bladder). Their fins were in the form of lobes, consisting of separate 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. Cis-fin fishes gave rise to the first amphibians - stegocephalic. On land in the Devonian, the first forests of giant ferns, horsetails and lyres appear. [...]

Of the general clinical changes in fish, the following are noted: depression of the general state, suppression and perversion of reactions to: external stimuli; darkening, pallor, hyperemia and hemorrhage on the skin of the body; ruffling of scales; violation of the sense of balance, orientation, coordination of movements and coordinated work of fins; conjunctivitis, keratitis "cataracts, corneal ulceration, bulging, loss of vision; complete or partial refusal to take feed; swelling of the abdomen (acute cases of poisoning); change in the rhythm of respiration and the amplitude of oscillation of the gill covers; periodic cramps of the muscles of the trunk, tremor of the gill covers and pectoral fins. With chronic intoxication, signs of increasing exhaustion develop. In severe processes, it 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 the content of CO2, 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, suppression of branchial respiration was noted with an increase in pCO2 in water, which can be removed by atropine. The effect of inhibition of pulmonary respiration under the influence of excess carbon dioxide was not observed in these fish, which suggests the presence of CO2-sensitive receptors in the gill region.

The exchange of gases, or respiration, is expressed in the absorption of oxygen by the body from the environment (water or atmosphere) and the release of carbon dioxide into the latter as the end product of the oxidative process taking place in the tissues, due to which the energy necessary for life is released. Oxygen is absorbed by the body in a variety of ways; they can mainly be characterized as: 1) diffuse respiration and 2) local respiration, 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 - the skin and the epithelial membrane of the digestive tube - to and organs specially adapted for this. This method of gas exchange is characteristic of some types of primitive multicellular animals, such as sponges, coelenterates and flat worms, 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 the square of the radius. Consequently, with a large body volume, this breathing method turns out to be insufficient.

However, even with more or less corresponding 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 contact area with an 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.

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

Gill breathing. There are external and internal gills. Primitive external gills are a simple protrusion of villous offshoots of the skin, abundantly supplied with capillary vessels. In some cases, such gills differ little in their function from diffuse respiration, being only a higher stage of it (Fig. 332- A, 2). They are usually concentrated in the anterior regions of the body.

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 adjacent skin forms abundant branching in the form of petals with a large number of capillary blood vessels. Internal gills are often covered with a special fold of the skin (gill cover), the oscillatory movements of which improve the exchange conditions, increasing the flow of water and removing the 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 by movements of the gill cover. In addition, their gills are included in the circulation. Each branchial 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, cutaneous respiration can also be preserved, but it is so weak that it is pushed into the background.

When describing the oropharynx of the digestive tract, it has already been said that the branchial apparatus is also characteristic of some invertebrates, such as, for example, semi-chordate and chordate animals.

Pulmonary respiration- an extremely perfect way of gas exchange, easily serving the organisms of massive animals. It is characteristic of terrestrial vertebrates: amphibians (not in a 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 breathing method requires the development of a very complex complex of organs.

When comparing aquatic and terrestrial respiration types of vertebrates, one important anatomical difference should be kept in mind. During gill breathing, portions of water, one after another, enter the primitive mouth and are released through the gill slits, where oxygen is extracted from it by the vessels of the gill folds. Thus, the inlet and a number of outlet openings are characteristic of the vertebrate gill respiration apparatus. In pulmonary respiration, the same openings are used for the introduction and removal of air. This feature, of course, is associated with the need to suck in and push out portions of air for faster ventilation of the gas exchange area, i.e., with the need for expansion and contraction of 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 that was being transformed into a lung; by its periodic contractions, air was pushed out of the bubble, and as a result of its expansion, due to the elasticity of the bubble walls, fresh portions of air were recruited. Elastic tissue, along with cartilaginous tissue, now dominates as a support in the respiratory organs.


Later, 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 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 necessary elasticity for this, as well as a small muscular apparatus as an auxiliary device.

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

Gas exchange in the lungs in terrestrial vertebrates, 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 are reduced 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 circulation.

The function of the breathing apparatus - to let 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 supporting material; in places in the form of bone tissue (nasal cavity), but mainly in the form of cartilaginous tissue and elastic tissue that is easily compliant, but quickly returns to normal.

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, attention is drawn to three peculiar areas. Of these, the initial-n-axis zone-serves for the perceived air, which is examined here for smell. The second section, the mouth, 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 - l e gk and e - represent the organ of direct exchange of gases.

Between the nasal cavity and the larynx there is a pharyngeal cavity common with the digestive apparatus, and breathing stretches between the larynx and the lung

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