Question 1. Describe the major changes in structure that occurred in the formation of the class of birds. What is their significance?
The emergence of the class of birds was accompanied by the following aromorphoses:
1. Progressive development of the nervous system of birds (development of the cerebral cortex, cerebellum, appearance of a thermoregulation center).
2. The appearance of a four-chambered heart in birds and complete separation of the blood circulation.
3. Formation of spongy lungs.
4. The emergence of warm-bloodedness (homeothermicity) as a result of progressive changes in the structure of the cardiovascular, nervous and respiratory systems.
Question 2. Describe the features of the appearance and internal structure of birds. Highlight the structural features that provide the possibility of flight.
Birds are a specialized class of higher vertebrates that have adapted to flight.
Features of the appearance of birds:
The body is covered with feathers;
The forelimbs are transformed into wings;
The shortened tail is equipped with tail feathers;
The jaws are without teeth, covered with horny sheaths that form a beak, the shape of which depends on the food consumed;
The neck is very mobile (the number of cervical vertebrae can reach 25 or more);
The structure of the legs depends on the habitat; Usually there are 4 clawed toes on the feet; the lower part of the legs is covered with horny scutes;
Dry skin; there are no glands, with the exception of the coccygeal gland (its secretion makes the feathers waterproof).
Question 3. What is the structure of a bird's feather? Explain the meaning of different types of feathers.
The structure and functions of feathers in different parts of the body differ significantly. The basis of the plumage is formed by contour feathers, consisting of a feather (part of the shaft immersed in the skin), a shaft and a fan. The fan is located on the sides of the rod and consists of elastic flat thread-like beards of the first order, on which, in turn, beards of the second order with hooks are located on both sides. The hooks interlock the beards with each other, ensuring the integrity of the fan and almost complete impermeability to air. Thanks to this structure, the bird's contour feather is light, flexible and almost impenetrable to air. In addition, with a sharp gust of wind or a blow, for example, against a branch, the beards of the fan part and the feather does not break. Then the bird extends the feather with its beak, the hooks interlock again and the structure of the feather is restored. Contour feathers perform different functions: the flight feathers form the plane of the wing, the tail feathers form the plane of the tail, and the integumentary feathers give the body a streamlined shape. Beneath the contour feathers lie down feathers and down. These feathers have a shortened shaft and no second-order barbules. They retain heat perfectly. Worn feathers are replaced with new ones during seasonal molts. In most species, feathers change gradually. But in ducks, swans, and geese, after hatching their chicks, all their flight feathers fall out at once. And for several weeks they cannot fly and hide in the bushes.
Question 4. How does the nervous system of birds differ from the nervous system of reptiles?
Compared to reptiles, birds have more developed forebrains, midbrains, and especially the cerebellum. Due to the development of the forebrain, adaptive behavior becomes more complex. Enlargement of the midbrain provides good vision for birds. The development of the cerebellum makes it possible to successfully coordinate complex movements during flight.
Question 5. Which sense organs are most well developed in birds?
Birds have very well developed vision. The organ of vision is the main one for orientation in the external environment. The eyeballs are large, equipped with two eyelids and a nictitating membrane. Visual acuity is very high, birds are able to distinguish colors and shades.
The hearing organ is similar to that of reptiles - it consists of the inner and middle ear, but is distinguished by higher sensitivity.
Question 6. What parts make up the digestive system of birds? What is bird's milk?
In the oral cavity, food is moistened with saliva and enters the pharynx. The long, stretchy esophagus sometimes forms a goiter, where food accumulates and begins to be digested by the secretions of special glands. The esophagus leads to the stomach, which consists of two sections - glandular and muscular. Digestion of food by gastric juice begins in the glandular section; mechanical processing of food occurs in the thick-walled muscular stomach, lined from the inside with a dense horn-like cuticle. Here the food is ground with specially swallowed small pebbles.
The small intestine is relatively long and receives the ducts of the liver and pancreas. The short large intestine (an adaptation for flight) opens into the cloaca.
The so-called “bird milk” is a fatty, curdled substance secreted from the walls of the crop during the nesting period, which birds (for example, pigeons) feed their chicks.
Question 7. From the description of the structure of the respiratory system of birds, highlight the characteristic features of air sacs. Define the term “air sacs”.
Associated with the lungs of birds are air sacs - transparent, elastic, thin-walled outgrowths of the mucous membrane of the secondary bronchi. The volume of the air sacs is approximately 10 times the volume of the lungs. One of the air sacs - interclavicular - unpaired, four paired - cervical, prothoracic, metathoracic, abdominal. Air sacs are located between the internal organs, and their processes penetrate under the skin and into the cavities of large bones (shoulder, hip, etc.)
During flight, air sacs protect the body from overheating and help cleanse the large intestine by periodically squeezing it.
At rest, a pigeon's breathing rate is 26 times per minute, and in flight - 400.
Question 8. What is the mechanism of double breathing in birds?
The respiratory system of birds is very unique; it consists of lungs and air sacs. The latter are located between the internal organs, muscles and go inside the hollow bones. The bronchi, entering the lungs, branch. Some penetrate through the lungs and into the air sacs. When you inhale, some of the air enters the lungs, and some goes into the air sacs. During exhalation, air from the air sacs enters the lungs, where gas exchange occurs. Thus, oxygen saturation of the blood occurs both during inhalation and exhalation. This phenomenon is called double breathing.
Question 9. Compile tables “Comparative characteristics of birds and reptiles.” (work in small groups)
1. The essence and significance of breathing processes
Breathing is the most ancient process through which the gas composition of the internal environment of the body is regenerated. As a result, organs and tissues are supplied with oxygen and give off carbon dioxide. Breathing is used in oxidative processes, during which energy is generated that is spent on growth, development and vital activity. The breathing process consists of three main parts - external respiration, gas transport by blood, and internal respiration.
External respiration is the exchange of gases between the body and the external environment. It is carried out through two processes - pulmonary respiration and respiration through the skin.
Pulmonary respiration involves the exchange of gases between alveolar air and the environment and between alveolar air and capillaries. During gas exchange with the external environment, air enters containing 21% oxygen and 0.03-0.04% carbon dioxide, and exhaled air contains 16% oxygen and 4% carbon dioxide. Oxygen flows from atmospheric air into the alveolar air, and carbon dioxide is released in the opposite direction. When exchanged with the capillaries of the pulmonary circulation in the alveolar air, the oxygen pressure is 102 mm Hg. Art., and carbon dioxide - 40 mm Hg. Art., venous blood oxygen tension – 40 mm Hg. Art., and carbon dioxide - 50 mm Hg. Art. As a result of external respiration, arterial blood, rich in oxygen and poor in carbon dioxide, flows from the lungs.
The transport of gases by blood is carried out mainly in the form of complexes:
1) oxygen forms a compound with hemoglobin, 1 g of hemoglobin binds 1.345 ml of gas;
2) 15–20 ml of oxygen is transported in the form of physical dissolution;
3) carbon dioxide is transported in the form of Na and K bicarbonates, with K bicarbonate located inside erythrocytes, and Na bicarbonate in the blood plasma;
4) carbon dioxide is transported along with the hemoglobin molecule.
Internal respiration consists of the exchange of gases between the capillaries of the systemic circulation and the tissue and interstitial respiration. As a result, oxygen is utilized for oxidative processes.
2. External respiration apparatus. Component meaning
In humans, external respiration is carried out using a special apparatus, the main function of which is the exchange of gases between the body and the external environment.
The external respiration apparatus includes three components - the respiratory tract, lungs, and chest along with the muscles.
The airways connect the lungs to the environment. They begin with the nasal passages, then continue into the larynx, trachea, and bronchi. Due to the presence of a cartilaginous base and periodic changes in the tone of smooth muscle cells, the lumen of the airways is always open. Its decrease occurs under the influence of the parasympathetic nervous system, and its expansion occurs under the influence of the sympathetic nervous system. The respiratory tract has a well-branched blood supply system, thanks to which the air is warmed and moistened. The epithelium of the airways is lined with cilia, which trap dust particles and microorganisms. The mucous membrane contains a large number of glands that produce secretions. Approximately 20–80 ml of secretion (mucus) is produced per day. The mucus contains lymphocytes and humoral factors (lysozyme, interferon, lactoferrin, proteases), immunoglobulins A, which provide a protective function. The respiratory tract contains a large number of receptors that form powerful reflexogenic zones. These are mechanoreceptors, chemoreceptors, taste receptors. Thus, the respiratory tract ensures constant interaction of the body with the environment and regulates the amount and composition of inhaled and exhaled air.
The lungs consist of alveoli, to which capillaries are adjacent. The total area of their interaction is approximately 80–90 m^2^. There is an air-hematic barrier between the lung tissue and the capillary.
The lungs perform many functions:
1) remove carbon dioxide and water in the form of vapor (excretory function);
2) normalize water exchange in the body;
3) are second-order blood depots;
4) take part in lipid metabolism during the formation of surfactant;
5) participate in the formation of various blood clotting factors;
6) provide inactivation of various substances;
7) take part in the synthesis of hormones and biologically active substances (serotonin, vasoactive intestinal polypeptide, etc.).
The chest, together with the muscles, forms a bag for the lungs. There is a group of inspiratory and expiratory muscles. The inspiratory muscles increase the size of the diaphragm, lift the anterior section of the ribs, expanding the anteroposterior and lateral openings, and lead to active deep inspiration. The expiratory muscles reduce the volume of the chest and lower the anterior ribs, causing exhalation.
Thus, breathing is an active process that is carried out only with the participation of all elements involved in the process.
3. Mechanism of inhalation and exhalation
In an adult, the respiratory rate is approximately 16–18 breaths per minute. It depends on the intensity of metabolic processes and blood gas composition.
The respiratory cycle consists of three phases:
1) inhalation phase (lasts approximately 0.9–4.7 s);
2) expiratory phase (lasts 1.2–6.0 s);
3) respiratory pause (non-permanent component).
The type of breathing depends on the muscles, so they distinguish:
1) chest. It is carried out with the participation of the intercostal muscles and muscles of the 1-3rd respiratory space; during inhalation, good ventilation of the upper part of the lungs is ensured, typical for women and children under 10 years of age;
2) abdominal. Inhalation occurs due to contractions of the diaphragm, leading to an increase in vertical size and, accordingly, better ventilation of the lower section, inherent in men;
3) mixed. It is observed with uniform work of all respiratory muscles, accompanied by a proportional increase in the chest in three directions, observed in trained people.
In a calm state, breathing is an active process and consists of active inhalation and passive exhalation.
Active inspiration begins under the influence of impulses coming from the respiratory center to the inspiratory muscles, causing them to contract. This leads to an increase in the size of the chest and, accordingly, the lungs. Intrapleural pressure becomes more negative than atmospheric pressure and decreases by 1.5–3 mm Hg. Art. As a result of the pressure difference, air enters the lungs. At the end of the phase, the pressures equalize.
Passive exhalation occurs after the impulses to the muscles cease, they relax, and the size of the chest decreases.
If the flow of impulses from the respiratory center is directed to the expiratory muscles, then active exhalation occurs. In this case, intrapulmonary pressure becomes equal to atmospheric pressure.
As the breathing rate increases, all phases are shortened.
Negative intrapleural pressure is the pressure difference between the parietal and visceral layers of the pleura. It is always below atmospheric. Factors that determine it:
1) uneven growth of the lungs and chest;
2) the presence of elastic traction of the lungs.
The growth rate of the chest is higher than that of the lung tissue. This leads to an increase in the volume of the pleural cavity, and since it is sealed, the pressure becomes negative.
Elastic traction of the lungs is the force with which the tissue tends to collapse. It occurs due to two reasons:
1) due to the presence of surface tension of the liquid in the alveoli;
2) due to the presence of elastic fibers.
Negative intrapleural pressure:
1) leads to expansion of the lungs;
2) provides venous return of blood to the chest;
3) facilitates the movement of lymph through the vessels;
4) promotes pulmonary blood flow, as it keeps the vessels open.
The lung tissue does not collapse completely even with maximum exhalation. This is due to the presence of surfactant, which lowers the tension of the fluid. Surfactant is a complex of phospholipids (mainly phosphotidylcholine and glycerol) formed by type II alveolocytes under the influence of the vagus nerve.
Thus, negative pressure is created in the pleural cavity, due to which the processes of inhalation and exhalation are carried out.
4. Concept of breathing pattern
Pattern is a set of temporal and volumetric characteristics of the respiratory center, such as:
1) respiratory rate;
2) duration of the respiratory cycle;
3) tidal volume;
4) minute volume;
5) maximum ventilation of the lungs, reserve volume of inhalation and exhalation;
6) vital capacity of the lungs.
The functioning of the external respiration apparatus can be judged by the volume of air entering the lungs during one respiratory cycle. The volume of air entering the lungs during maximum inspiration forms the total lung capacity. It is approximately 4.5–6 liters and consists of the vital capacity of the lungs and residual volume.
The vital capacity of the lungs is the amount of air that a person can exhale after a deep breath. It is one of the indicators of the physical development of the body and is considered pathological if it is 70–80% of the proper volume. During life, this value may change. This depends on a number of reasons: age, height, body position in space, food intake, physical activity, presence or absence of pregnancy.
The vital capacity of the lungs consists of tidal and reserve volumes. Tidal volume is the amount of air that a person inhales and exhales at rest. Its size is 0.3–0.7 l. It maintains the partial pressure of oxygen and carbon dioxide in the alveolar air at a certain level. Inspiratory reserve volume is the amount of air that a person can additionally inhale after a quiet breath. As a rule, this is 1.5–2.0 liters. It characterizes the ability of lung tissue to undergo additional stretching. Expiratory reserve volume is the amount of air that can be exhaled following a normal exhalation.
Residual volume is the constant volume of air remaining in the lungs even after maximum exhalation. Makes up about 1.0–1.5 liters.
An important characteristic of the respiratory cycle is the frequency of respiratory movements per minute. Normally it is 16–20 movements per minute.
The duration of the respiratory cycle is calculated by dividing 60 s by the respiratory rate.
Entry and expiration times can be determined using a spirogram.
Minute volume is the amount of air exchanged with the environment during quiet breathing. It is determined by the product of the tidal volume and the respiratory frequency and is 6–8 liters.
Maximum ventilation of the lungs is the largest amount of air that can enter the lungs in 1 minute with intense breathing. On average, its value is 70-150 liters.
Indicators of the respiratory cycle are important characteristics that are widely used in medicine.
What is the mechanism of double breathing in birds?
Answers:
Due to flight, birds have a unique structure of their respiratory organs. Bird lungs are dense, spongy bodies. The bronchi, having entered the lungs, branch strongly into the thinnest, blindly closed bronchioles, entangled in a network of capillaries, where gas exchange occurs. Some of the large bronchi, without branching, extend beyond the lungs and expand into huge thin-walled air sacs, the volume of which is many times greater than the volume of the lungs (Fig. 11.23). Air sacs are located between various internal organs, and their branches pass between the muscles, under the skin and in the cavities of the bones. The act of breathing in a flightless bird is carried out by changing the volume of the chest due to the approach or distance of the sternum from the spine. In flight, such a breathing mechanism is impossible due to the work of the pectoral muscles, and it occurs with the participation of air sacs. When the wings rise, the bags stretch and air is forcefully sucked through the nostrils into the lungs and then into the bags themselves. When the wings lower, the air sacs are compressed and the air from them enters the lungs, where gas exchange occurs again. The exchange of gases in the lungs during inhalation and exhalation is called double breathing. Its adaptive significance is obvious: the more often a bird flaps its wings, the more actively it breathes. In addition, air sacs protect the bird's body from overheating during fast flight.
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Similar questions
The bird is unique, it is adapted to regular flights. Double breathing, which has developed as a result of evolutionary transformations, contributes to better gas exchange in the body of birds.
Upper respiratory tract
The path of air in the body of birds begins with the laryngeal slit, through which it enters the trachea. The part of it located on top is the larynx. It is called the upper one; it does not play any role in sound formation. The voice of birds originates in the lower larynx, which is unique to birds. It is located where the trachea divides into two bronchi, and is an extension that is supported by rings of bones.
Inside the larynx itself there are vocal membranes attached to the walls. Under the action of the singing muscles, they change configuration, which leads to a wide variety of sounds produced. The internal vocal membranes are located below where the trachea divides.
The upper ones are important for regulating body temperature. The heat causes the bird to breathe frequently and shallowly. The blood vessels located in the mouth and throat dilate. As a result, the bird’s body cools, giving off heat to the exhaled air.
Light and air bags
Birds are different from amphibians and reptiles, in which they resemble empty bags. In feathered fauna, this organ is attached to the back of the chest. In composition it resembles a dense sponge. The branched bronchi have bridges - parabronchi with a large number of dead-end canals (bronchioles), which are intertwined with a dense network of capillaries.
Some bronchi, after branching, become large air sacs with thin walls. Their volume is much larger than that of the lungs. Birds have several air sacs:
- 2 neck,
- interclavicular,
- 4-6 breasts,
- 2 abdominal.
The channels go under the skin and connect to the pneumatic bones.
Double breathing exists precisely thanks to air sacs. With their help, the breathing mechanism is determined during flight.
Double Breathing
A resting bird that sits renews the air in its lungs by working its muscles. As the sternum descends, oxygen-rich gas is drawn into the respiratory organ. By the reverse movement of the muscles, the air is pushed out. The lungs also help pump in oxygen.
A bird that walks or climbs uses air sacs located in the peritoneum to work. The upper parts of the legs put pressure on them.
In flight, the importance of air sacs increases many times over, because the bird’s process of double breathing occurs. Step by step it looks like this:
- The wings rise, stretching the air sacs.
- Air is forced into the lungs.
- Part of the gas, without stopping, passes into the air sacs without losing oxygen. Gas exchange does not occur in this organ.
- The wings lower, and as you exhale, oxygen-rich gas from the air sacs passes through the lungs.
The phenomenon in which the blood is saturated with oxygen during inhalation and exhalation is called double breathing. It has great significance in the life of birds. Breathing becomes faster as the intensity of the wing flapping increases.
Other breathing features
Double breathing is typical for birds, but in some birds the number of flapping and breathing movements does not coincide. However, certain stages of these processes correspond in time. The presence of air sacs helps prevent birds from overheating in flight because cold air flows around the body from the inside. With their help, body density and friction of organs against each other are reduced. The frequency of respiratory movements differs among different species. The volume of air sacs is an order of magnitude greater than that of lungs.
Respiratory system They are extremely unique and more than any other system of internal organs they are adapted to the aerial lifestyle.
The laryngeal fissure leads into the trachea, the upper part of which forms the larynx, supported by the unpaired cricoid cartilage and paired arytenoid cartilages. This larynx in birds is known as the upper larynx and does not play the role of a vocal apparatus. This function is performed by the so-called lower larynx, characteristic only of birds. It is located at the point where the trachea divides into two bronchi and represents an expansion supported by bony rings. The external vocal membranes protrude into the cavity of the larynx from its outer walls, and from below, from the branching point of the trachea, the internal vocal membranes protrude. The vocal membranes, due to the contraction of special singing muscles, can change their position and shape, which determines the variety of sounds they produce.
The upper respiratory tract is important for thermoregulation. It has been established that as the external temperature rises, the breathing of birds sharply increases and becomes shallow. At the same time, a very strong expansion of the blood vessels in the oral cavity and pharynx occurs. Therefore, increased heat transfer from the bird’s body occurs.
The lungs of birds are not hollow sacs, as in amphibians and partly reptiles, but dense spongy bodies attached to the dorsal wall of the chest. The bronchi, entering the lungs, branch, and their main branches pierce the lungs through and into the air sacs. The branches of the bronchi are connected to each other by thin canals - parabronchi, from which in turn arise many blind tubules - bronchioles. Around the latter, capillaries of blood vessels branch.
Some of the branches of the bronchi, as said, extend beyond the lungs themselves and expand into huge thin-walled air sacs, the volume of which is many times greater than the volume of the lungs. Air sacs are located between various internal organs, and their branches pass between the muscles under the skin and enter the pneumatic bones. Birds have several air sacs: two cervical, one interclavicular, two or three pairs of thoracic and one pair of very large abdominal ones.
The significance of air sacs is very great and varied. Their main role is that they determine the breathing mechanism, especially during flight. Breathing of a sitting bird is carried out by removing and bringing the sternum closer relative to the spine, which is associated with a change in the angles between the movably articulated thoracic and dorsal parts of the ribs. As the sternum descends, the volume of the chest increases, the corresponding air sacs stretch and the sucked air passes through the lungs. When the sternum is raised, air is pushed out. At the same time, the lungs themselves play the role of pumps. When walking and climbing, the abdominal air sacs also act, on which the upper parts of the hind limbs press.
During flight, the role of air sacs as a pumping organ is great. When the wings rise, they stretch, and air is forcefully sucked into the lungs and further into the bags. Gas exchange does not occur in the bags; air is sucked into them when you inhale and passes through the lungs so quickly that it does not have time to give much oxygen to the blood. As a result, oxygen-rich air enters the air sacs. When the wings lower, exhalation occurs and air with a high oxygen content is blown through the lungs. Consequently, at this phase of the act of breathing, blood oxidation occurs again. This phenomenon is called double breathing. Its adaptive significance is quite obvious. The more often a bird flaps its wings, the more intensely it breathes. An increase in breathing energy is achieved automatically in a flying bird, as the work of the wings increases and the need for oxygen increases.
However, complete synchronization of flapping and respiratory movements is not observed in all birds. For many, the number of strokes exceeds the number of breathing movements. At the same time, the beginning of a sigh or exhalation coincides with a certain phase of the wing flap. This mechanism is referred to as breathing coordination. Typically, the beginning of the inhalation coincides with the middle or end of the upward stroke, and the beginning of the exhalation coincides with the end of the downward movement of the wing.
The famous zoophysiologist Schmidt-Nielsen (1976) expressed a slightly different concept of lung ventilation, according to which air through the main middle bronchus, which gives off almost no branches to the lung parenchyma, goes directly to the posterior air sacs. From the latter, it enters the lungs, then into the anterior air sacs, from which it is pushed out. Thus, according to this view, the circulation of air in the respiratory system is unidirectional.
In addition to participating in the act of breathing, air sacs have other, less significant functions. Thus, during a flight, when the body is working hard, they protect it from overheating, since the relatively cold air “flows around” almost all the internal organs, and partly the muscles. In addition, air sacs reduce friction between organs during flight. Finally, they reduce body density, increase intra-abdominal pressure and promote defecation.
The total volume of the air sacs is approximately 10 times greater than the volume of the lungs. The respiratory rate varies among species.
In a pigeon at rest, the number of respiratory movements per minute is on average 26, when walking - 77, in flight - 400. (At the same time, pulmonary ventilation is 2.5 times greater than the need for metabolic gas exchange and serves to discharge excess heat with pulmonary evaporation It should be noted that heat reduction in flight is 8 times greater than at rest.)
As a rule, small birds have a greater work of breathing than large birds. The average number of respiratory movements per minute in a duck is 30-43, in small passerines - 90-100.
Accordingly, small birds consume significantly more oxygen than large birds and, therefore, have a more intense metabolism. Thus, a hummingbird with a body weight of 3 to 7 g consumes from 4 to 10 ml of oxygen per 1 hour per 1 g of body weight; A jayfish with a body weight of 71 g consumes 1.75 ml, a pigeon with a body weight of 150 g consumes 0.98, and an emu with a body weight of 38 kg consumes 0.023 ml. This is one example of a general inverse relationship between body size and metabolic rate of homeothermic animals. Let us point out for comparison that in phylogenetically lower reptiles this figure is only 0.1-0.3.
Blood pressure levels also confirm the high level of metabolism in birds. So. In a pigeon it is 135\105, and in scaly reptiles it is 80\60-14\10.
