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Decrease in the number of gills.

An increase in the respiratory surface due to the formation of branchial lobes.

The formation of branchial capillaries.

In the lancelet, the lateral walls of the pharynx are penetrated by numerous (up to 150 pairs) obliquely located branchial slits. The gill arteries approach the intergill septa, and the outgoing gill arteries branch off. When water washes between the gill septa, gas exchange occurs between the passing water and the blood that flows through the thin vessels of the septum. The branchial arteries do not branch into capillaries. In addition, oxygen is released into the animal's body through the capillaries of the skin.

In primary-water vertebrates (jawless and fish), as in the lower chordates, gill slits are formed connecting the pharyngeal cavity with the external environment. In cyclostomes, from the endoderm lining the gill slits, gill sacs are formed (in fish, gills develop from the ectoderm). The inner surface of the sacs is covered with numerous folds - gill petals, in the walls of which a dense network of capillaries branches. The sack opens with an internal narrow channel into the pharynx (in adult lampreys, into the respiratory tube), and with an external one, on the lateral surface of the animal's body. In myxine there are from 5 to 16 pairs of branchial sacs, in the Bdellostomaceae family, each of them opens outward with an independent opening, and in the myxine family, all external gill ducts on each side merge into one canal, which opens outward with one hole located far behind. Lampreys have 7 pairs of gill sacs, each of which opens outward with an independent opening. Breathing is carried out by rhythmic contractions and relaxation of the muscular wall of the branchial region. In non-feeding lampreys, water enters the respiratory tube from the oral cavity, then washes the petals of the gill sacs, providing gas exchange, and is removed through the external gill ducts. In feeding cyclostomes, water enters and is removed through the external openings of the gill sacs.

The respiratory system of fish has specialized organs of gas exchange - ectodermal gills, which are either located on the intergill septa, like in cartilaginous fish, or directly depart from the gill arches, like in bony fish. The exchange of gases in the gills of vertebrates is built according to the type of "countercurrent systems": with the oncoming movement, the blood comes into contact with oxygen-rich water, which ensures its effective saturation. The increase in the surface of oxygen absorption due to the formation of gills was accompanied by a decrease in the number of branchial slits in vertebrates as compared with the lower chordates. In whole-headed fish (from cartilaginous fish), a reduction of the intergill septa is observed and a leathery gill cover is formed, which covers the outside of the gills. In bony fish, a bony skeleton appears in the operculum, and the intergill septa are reduced, which contributes to more intensive washing of the gill lobes with water. Along with gas exchange, the gills of fish participate in water and salt metabolism, in the elimination of ammonia and urea from the body. The skin, swim bladder, supraopharyngeal labyrinths, and specialized sections of the intestinal tube function as additional respiratory organs in certain groups of fish. In lung-breathing and multi-feather-like fish, organs of air respiration appear - the lungs. The lungs arise as paired outgrowths of the abdominal part of the pharynx in the region of the last branchial slit and are connected with the esophagus by a short canal. The walls of this outgrowth are thin and are abundantly supplied with blood.

Trends in the evolution of pulmonary respiration

The emergence and differentiation of the respiratory tract.

Differentiation of the lung and an increase in the respiratory surface.

Development of auxiliary organs (chest).

In amphibians, the following are involved in the absorption of oxygen and the release of carbon dioxide: in the larvae - the skin, external and internal gills, in adults - the lungs, skin and mucous membrane of the oropharyngeal cavity. In some species of tailed amphibians (sirens, proteas) and in adults, gills remain and the lungs are underdeveloped or reduced. The ratio of pulmonary and other types of gas exchange is not the same: in species of humid habitats, skin respiration dominates in gas exchange; in inhabitants of dry places, most of the oxygen enters through the lungs, but the skin plays an essential role in the release of carbon dioxide. The respiratory system of adult amphibians includes the oropharyngeal, laryngeal-tracheal cavities and saccular lungs, the walls of which are braided with a dense network of capillaries. In tailless amphibians there is a common laryngeal-tracheal chamber; in caudates, it is divided into the larynx and trachea. Arytenoid cartilages appear in the larynx, which support its wall and vocal cords. The lungs of tailed amphibians are two thin-walled sacs without partitions. In tailless, inside the lung sacs, there are partitions on the walls that increase the surface of gas exchange (cellular lungs). Amphibians have no ribs, and the act of breathing occurs by forcing air during inhalation (by increasing and then decreasing the volume of the oropharyngeal cavity) and pushing out air during exhalation (due to the elasticity of the walls of the lungs and abdominal muscles).

In reptiles, further differentiation of the airways and a significant increase in the functional surface of gas exchange in the lungs are noted. The airways are divided into the nasal cavity (it is combined with the oral cavity, but in crocodiles and turtles, these cavities are separated by the bony palate), the larynx, the trachea and two bronchi. The walls of the larynx are supported by paired arytenoid and unpaired cricoid cartilages. In lizards and snakes, the inner walls of the pulmonary sacs have a folded cellular structure. In turtles and crocodiles, a complex system of septa protrudes into the inner cavity of the lung so deeply that the lung acquires a spongy structure. The ribcage is formed: the ribs are movably connected to the spine and sternum, the intercostal muscles develop. The act of breathing is carried out due to a change in the volume of the chest (costal type of breathing). Turtles retain the oropharyngeal type of air injection. In aquatic turtles in water, additional respiratory organs are the outgrowths of the pharynx and cloaca (anal vesicles) rich in capillaries. Reptiles lack skin respiration.

In birds, the airways are represented by the nasal cavity, the larynx, which is supported by arytenoid and cricoid cartilages, a long trachea and the bronchial system. The lungs are small, dense and not very extensible and are accreted to the ribs on the sides of the spinal column. Primary bronchi are formed when the lower part of the trachea is divided and enter the tissue of the corresponding lung, where they break up into 15–20 secondary bronchi, most of which end blindly, and some of them communicate with air sacs. Secondary bronchi are interconnected by smaller parabronchi, from which many thin-walled cellular bronchioles depart. The bronchioles braided by blood vessels form the morphofunctional structure of the lung. Air sacs are associated with the lungs of birds - transparent elastic thin-walled outgrowths of the mucous membrane of the secondary bronchi. The volume of the air sacs is about 10 times the volume of the lungs. They play a very important role in the implementation of a kind of breathing act of birds: air with a high oxygen content enters the lungs both during inhalation and exhalation - "double breathing". In addition to intensifying breathing, air bags prevent the body from overheating during intense movement. The increase in intra-abdominal pressure during expiration promotes defecation. Diving birds, by increasing the pressure in the air sacs, can decrease the volume and thereby increase the density, which facilitates immersion in the water. Cutaneous respiration in birds is absent.

In mammals, further differentiation of the airways is observed. A nasal cavity, nasopharynx is formed, the entrance to the larynx is covered by the epiglottis (in all terrestrial vertebrates, except for mammals, the laryngeal slit is closed by special muscles), thyroid cartilage appears in the larynx, then the trachea, which branches into two bronchi, going into the right and left lungs, appears. In the lungs, the bronchi repeatedly branch and end with bronchioles and alveoli (the number of alveoli is from 6 to 500 million), this significantly increases the respiratory surface. Gas exchange occurs in the alveolar passages and alveoli, the walls of which are densely braided with blood vessels. The morphofunctional unit of the mammalian lung is the pulmonary acinus, which is formed as a result of the branching of the terminal bronchiole. The rib cage is formed, which is separated from the abdominal cavity by the diaphragm. The number of respiratory movements is from 8 to 200. Respiratory movements are carried out in two ways: by changing the volume of the chest (costal breathing) and due to the activity of the diaphragmatic muscle (diaphragmatic breathing). Higher mammals have developed cutaneous respiration through the system of cutaneous capillaries, which plays an important role in gas exchange.

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 that open into the cloaca, they are excreted.

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.

Respiratory system evolution

The stages of the breathing process

Breath- a set of processes that ensure the supply of oxygen from the environment to the body, which is necessary for the oxidation of organic substances in the mitochondria of the cell, and the release of carbon dioxide

Breathing types:

Breath type:

Cellular.
Organisms: unicellular animals (amoeba, euglena green, infusoria shoe); coelenterates (jellyfish, coral polyps); some worms.

Single-celled organisms absorb oxygen dissolved in water through the entire surface of the body by diffusion.

Oxygen participates in the breakdown of complex organic substances, as a result of which energy is released, which is necessary for the life of the animal.
The carbon dioxide generated by breathing is released to the outside through the entire surface of the body.

Tracheal breathing is breathing with the help of a system of united tracheal tubes that permeate the entire body.

Organisms: class Insects (beetles, butterflies, grasshoppers, flies)

The belly of the insect is divided into 5–11 parts (segments). Each of them has a pair of small holes - spiracles. Branching tubules extend inward from each spiracle - trachea that permeate the entire body of the insect. Observing the May beetle, one can notice how its abdomen either decreases in volume or increases. These are breathing movements. When inhaling, air containing oxygen enters the body through the spiracles, and when exhaling, air saturated with carbon dioxide comes out.

In spiders (class Arachnids), the respiratory organs are represented not only by the trachea, but also by the pulmonary sacs, which communicate with the external environment through the respiratory openings.

Gill breathing is breathing through specialized formations with a dense network of blood vessels.

Organisms: many aquatic life (fish, crayfish, molluscs)

Fish breathe oxygen dissolved in water through special branched skin outgrowths called gills. Fish constantly swallow water. From the oral cavity, water passes through the gill slits, washes the gills and comes out from under the gill covers. Gills consist of branchial arches and gill lobes which are permeated by many blood vessels. Oxygen enters the blood from the water that washes the gills, and carbon dioxide is removed from the blood into the water. The gills inside the body are called internal gills.
Some animals, such as amphibians, have thick tufts of gills on the surface of the body. Such gills are called - outdoor. Such is the structure of Proteus, a blind cave animal from the western regions of Yugoslavia, and axolotls (which in general appearance are similar to newts) - their homeland is Mexico.

The set of processes that ensure the consumption of O 2 and the release of CO 2 in the body is called breathing... There are processes of external and internal respiration. External respiration provides 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 using special vehicles (blood, hemolymph).

The amount of oxygen entering the tissues of an animal depends on the area of ​​the respiratory surface and the difference in oxygen concentration on them. Therefore, in all respiratory organs, the growth of the respiratory epithelium is observed. To maintain a high gradient of oxygen diffusion on the exchange membrane, it is necessary to move the medium (ventilation). It is provided by respiratory rhythmic movements of the whole body of the animal (small-bristled tubule worm, 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 one is characteristic of animals with specialized respiratory organs. For example, in eels with gills, 60% of oxygen demand is provided by cutaneous respiration; in frogs with lungs, this value is more than 50%.

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

Gills are organs located outside the body cavity in the form of epithelial surfaces pierced by a dense network of blood capillaries. Gill respiration is characteristic of polychaete annelids, most molluscs, crustaceans, fish, and amphibian larvae. The gill respiration is most effective in fish. It is based on counterflow phenomenon: the blood in the capillaries of the gill lobes flows in the opposite direction to the flow of the ox that washes the gills.

Lungs are usually 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: pulmonary molluscs, scorpions, spiders. Only terrestrial vertebrates have ventilation lungs.

The complication of the structure of the lungs in the order 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. A similar indicator for the epithelium of the human lungs is 300 cm 2.

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

The third type of respiratory system is trachea... They are thin-walled, branching, non-collapsing invaginations into the body, filled with air. The trachea communicate with the external environment through openings in the cuticle - spiracles. Insects 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. With a high degree of development of the tracheal system (in insects), its numerous ramifications entwine all internal organs and directly provide gas exchange in tissues. The fundamental difference between tracheal respiration and pulmonary and branchial 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 ensuring 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, in 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 a closed tracheal system enter the "gills" - appendages with a large surface and a thin cuticle that allows gas exchange between water and air in the tracheal system. Such tracheal gills are found, for example, in mayfly larvae. In the larvae of some dragonflies, the tracheal gills are located in the rectal cavity, and the insect ventilates them, drawing water into the intestine and pushing it back.

Breathing evolution.

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

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

Gill breathing

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

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

In the lancelet, the gill slits penetrate the pharynx and open into the peri-occipital cavity with frequent water changes.

In fish, gills are made of gill arches with gill lobes pierced with capillaries. The water swallowed by the fish enters the oral cavity, passes through the gill lobes to the outside, washes them and supplies the blood with oxygen.

4) Tracheal and pulmonary respiration- more efficient, since oxygen is absorbed directly from the air, and not from water. Typical for terrestrial mollusks (saccular lungs), arachnids, insects, amphibians, reptiles, birds, mammals.

SPIDER have pulmonary sacs (scorpions), trachea (mites), and spiders have both.

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

AMPHIBIAN have 2/3 cutaneous respiration and 1/3 pulmonary respiration. For the first time, airways appear: larynx, trachea, bronchial rudiments; lungs - smooth-walled bags.

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

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

Air bags- air cavities connected to the respiratory system, 10 times larger than the volume of the lungs, serving to enhance air exchange in flight, do not perform the function of gas exchange. Resting breathing is carried out by changing the volume of the chest.

Breathing in flight:

1. When the wings rise, air is sucked into the lungs and back air sacs through the nostrils (gas exchange in the lungs);

Front air bags ← lungs - rear air bags

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

Front air bags - light ← rear air bags

Double breathing Is the exchange of gases in the lungs during inhalation and exhalation.

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

Airways: nasal cavity → nasopharynx → pharynx → larynx → trachea → bronchi (bronchi branch into bronchioles, alveolar passages and end with alveoli - pulmonary vesicles). Lungs of a spongy structure consist of alveoli, braided by capillaries. The respiratory surface is increased 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. Complete separation of the oral and nasal cavity. Mammals can breathe and chew at the same time.