Bird respiratory system. Bird Owner's Encyclopedia

Respiratory system

The respiratory system of birds has important features associated with flight. A long trachea emerges from the larynx, which divides into two central bronchi (Fig. 1). At the point where the trachea divides into the bronchi there is an extension - the lower larynx, which plays the role of the vocal apparatus - it contains the vocal cords. The lower larynx is well developed in songbirds and species that produce loud sounds.

Rice. 1. Diagram of the respiratory system of a bird: 1 - trachea; 2 - front air bags; 3 - central bronchus; 4 - lung; 5 - rear air bags
The lungs of birds, unlike the lungs of reptiles, are dense, spongy bodies. Their bulk consists of numerous tubes (secondary and tertiary bronchi) - the result of the branching of the central bronchi. Their walls are densely braided with capillaries: gas exchange takes place here.

Rice. 2. Diagram of the structure of air sacs.
Breathing during and outside of flight.
The lungs are designed in such a way that air passes through them. When you inhale, only 25% of the outside air remains directly in the lungs, and 75% passes through them and enters special air sacs (Fig. 2).
During inhalation, the central bronchi supply air to both the lungs and the posterior air sacs.
When you exhale, air from the lungs passes into the front air sacs, and from the rear air sacs into the lungs, forming the so-called double breathing. Thus, the lungs are constantly saturated with oxygen, both during inhalation and exhalation. In the lungs, oxygen saturates the blood. The rest of the air passes into the anterior air sacs, from them into the central bronchi and through the trachea to the outside. The air always flows in one direction - from the back bags through the lungs to the front bags. Thus, air sacs play an important role in breathing. Their volume is 10 times greater than the volume of the lungs, which reduces the bird’s body density. The entry of fresh portions of air into the rear air sacs located between the organs protects the bird’s body from overheating during flight.
At rest, the bird breathes by expanding and contracting the chest. During flight, when moving wings need solid support, the bird's chest remains practically motionless and the passage of air through the lungs is determined by the expansion and compression of the air sacs. The faster the flapping flight, the more intense the breathing. When the wings rise, they stretch and air is independently sucked into the lungs and air sacs. When the wings lower, exhalation occurs and air from the bags passes through the lungs.
Voice apparatus
The vocal apparatus of birds has not one larynx, but two - upper and lower. The main role in the formation of sounds belongs to the lower one, which is very complex. Its very presence distinguishes birds from other animals. It is located in the lower part of the trachea where the trachea branches into two main bronchi.
The vocal apparatus occupies a significant part of the body, which is especially typical for small birds, in which the entire body is involved in the process of singing.

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.

The respiratory apparatus of birds consists of: nasal cavity, upper larynx, trachea, lower larynx, bronchi, lungs, air sacs.

Respiration is the process of exchanging gases between the body and the environment, releasing respiratory moisture and with it heat, oxidizing nutrients and releasing energy for the needs of the body. An animal organism needs a constant supply of oxygen and the release of carbon dioxide.

The breathing process includes external (pulmonary) respiration (exchange of gases between the body and the external environment in the lungs), internal (tissue) respiration (processes of gas exchange in cells) and the transport of oxygen from the lungs to the tissues by the blood, and carbon dioxide in the opposite direction.

The respiratory organs of birds ensure the exchange of gases between the body and the environment, and participate in the regulation of water, heat exchange and acid-base balance.

The nasal cavity is short, divided by a bony and partially cartilaginous septum, located in the upper part of the beak. At the base of the beak there are nostrils of small diameter. In each half of the nasal cavity there are three nasal conchae in the form of curls of cartilage.

The nasal cavity is an organ where air is filtered and freed from mechanical impurities. A large number of blood capillaries in the cavity help heat the air. The nasal cavity is connected through the choanae to the oropharyngeal cavity, so air from it can enter the trachea.

Respiratory system of a bird. Photo: wikimedia.

The upper larynx is located behind the posterior edge of the tongue, between the lingual bone and the choanae, in the form of an oval or round pillow, divided by a longitudinal fissure - the entrance of the larynx.

The larynx is bounded laterally by the annular and two arytenoid cartilages. In front of the entrance to it there is an epiglottis in the form of a small transverse fold with papillae, which protects against food masses entering the larynx.

The annular cartilage, which is the basis of the larynx, consists of an upper, lower and two lateral parts. The lower part consists of an ossified plate, the rest are made of hyaline cartilage. Birds do not have vocal cords in the upper larynx.

The lower (singing) larynx is located at the end of the trachea, at the site of its bifurcation. It is formed by the last three rings of the trachea, which are connected in chickens or completely ossify in geese and drakes. The result is a drum for sound resonance. The left bronchus also participates in the formation of the drum. The cartilaginous septum of the singing larynx, consisting of the last ring of the trachea, protrudes into the lower part of the drum cavity. There are glottis. The muscles of the lower larynx can quickly contract or relax and thereby tighten or weaken the membranes; the air flowing from the lungs causes them to vibrate. In chickens, in the lower larynx there are two connective tissue folds that vibrate as air passes, producing sound. In songbirds, these muscles are more differentiated than in other species (there can be up to seven pairs of them).

The trachea is a hollow, relatively long tube consisting of cartilaginous or ossified rings, which are connected to each other by short interring connective tissue ligaments. The diameter of the trachea is the same along its entire length; sometimes the trachea is somewhat narrowed at the lower end and widened in one or two places in the middle. The trachea forms curves, so its length exceeds the length of the neck. Having entered the chest cavity, the trachea divides into two bronchi. The trachea is driven by two muscles - the clavicular tracheal and sternotracheal muscles, which accompany it.

Bronchi. In the chest cavity, behind the sternum, the trachea is divided into two main bronchi, 6-7 mm long and 5-6 mm in diameter. One of them enters the right and the other enters the left lung. Having entered the lungs, both trunks of the main bronchi expand in an ampulla-like manner at the beginning of the second third of the ventral surface, lose their cartilaginous rings and continue to the end of the lungs in the form of membranous canals, then flow into the corresponding abdominal air sacs with a caudal opening. The section of the main bronchus, surrounded by cartilaginous rings, passing through the entire lung, is called the mesobronchi, and the place of its ampulla-shaped expansion is the vestibular part.

Bronchioles and funnels form a system of air tubes and air funnels extending from them in the shape of a hexagonal prism. The entire system of airways is a dense network of horizontal and vertical (large and small sizes) air tubes, similar in design to an arachnoid network. The walls of the bronchioles consist of delicate connective tissue, penetrated by a network of tiny blood vessels (capillaries). The latter wrap around the airways and are woven into the network of bronchioles, creating close contact between the blood vessels and the airways, ensuring gas exchange in the lungs.

The lungs of birds are light red in color, spongy in structure, shaped like elongated sachets, and low in elasticity. The lungs perform one of the main functions in general gas exchange. They receive atmospheric oxygen, which passes into the blood through the epithelial cells of the smallest respiratory tubes and the endothelium of the capillaries. With exhaled air, carbon dioxide and moisture are released through the lungs.

The lungs are located in the chest cavity on the sides of the spinal column, occupying the space from the first rib to the cranial edge of the kidney. The lungs do not lie freely. With their upper (dorsal) surface they are pressed between the ribs and are firmly connected to them. The grooves formed by the ribs are clearly visible on the surface of the lungs. The lower surface of the lungs is smooth and covered with pleura.

Air sacs are thin-walled structures that are filled with air. They are an extension of the bronchi and continue them. The walls of the sacs contain a dense network of blood vessels. The air sacs connect at one end to the bronchi, and some of them give off processes (diverticula) to the bones that have air cavities. In total, there are nine main bags in the bird’s body, including four paired ones, located symmetrically on both sides, and one unpaired one.

Paired bags include: cervical, thoracic anterior and posterior, abdominal, or abdominal. The unpaired air sac is the clavicular sac. The air sacs are divided into inspiratory (abdominal and posterior thoracic) and expiratory (anterior thoracic, cervical and clavicular).

Inhalation air sacs. The main bronchus at the posterior edge of the lung branches and, expanding, forms inhalational air sacs - abdominal and posterior thoracic.

The abdominal sacs are the largest of all the air sacs available. They are located on the sides of the abdominal cavity and form diverticula to the pelvic and sacral bones.

The posterior thoracic (diaphragmatic) sacs are located in the area of ​​the diaphragm, between the thoracic and abdominal cavities, cranial to the air-bearing abdominal sacs and ventral to the abdominal organs.

Exhalatory air sacs. The anterior thoracic sacs are located cranial to the metathoracic air sacs, are supplied with air from the anterior thoracic bronchi, and do not have processes to the bones.

The cervical sacs are located in the lower part of the neck, extended towards the skull parallel to the cervical vertebrae. They communicate with the cervical and thoracic vertebrae, as well as with the vertebral part of the ribs.

The clavicular air sac is located caudal to the clavicle. It is filled with air from the clavicular bronchus, which departs from the main bronchus at the very beginning of the lung. The clavicular sac has lateral diverticula - axillary sacs that go to the humerus and chest bones, to the ribs and bones of the shoulder girdle.

Unlike mammals, the respiratory system of birds has structural and functional features. Structural features. The nasal openings in birds are located at the base of the beak; The nasal air passages are short.

Under the external nostril there is a scaly, fixed nasal valve, and around the nostrils there is a corolla of feathers that protects the nasal passages from dust and water. In waterfowl, the nostrils are surrounded by a waxy skin.

Birds lack an epiglottis. The function of the epiglottis is performed by the back of the tongue. There are two larynxes - upper and lower. There are no vocal cords in the upper larynx. The lower larynx is located at the end of the trachea at the point where it branches into the bronchi and serves as a sound resonator. It has special membranes and special muscles. Air passing through the lower larynx causes the membrane to vibrate, resulting in sounds of different pitches. These sounds are amplified in the resonator. Chickens are capable of making 25 different sounds, each of which reflects a particular emotional state.

The trachea in birds is long and has up to 200 tracheal rings. Behind the lower larynx, the trachea divides into two main bronchi, which enter the right and left lungs. The bronchi pass through the lungs and expand into the abdominal air sacs. Inside each lung, the bronchi give rise to secondary bronchi, which go in two directions - to the ventral surface of the lungs and to the dorsal one. The ecto- and endobronchi are divided into a large number of small tubes - parabronchi and bronchioles, and the latter already pass into many alveoli. Parabronchi, bronchioles and alveoli form the respiratory parenchyma of the lungs - the “arachnoid network”, where gas exchange takes place.

The lungs are elongated, low-elastic, pressed between the ribs and firmly connected to them. Since they are attached to the dorsal wall of the chest, they cannot expand like the lungs of mammals, which are free in the chest. The lung weight of chickens is approximately 30 g.

Birds have the rudiments of two diaphragm lobes: pulmonary and thoracoabdominal. The diaphragm is attached to the spinal column by tendons and small muscle fibers to the ribs. It contracts in connection with inhalation, but its role in the mechanism of inhalation and exhalation is insignificant. In chickens, the abdominal muscles play a large part in the act of inhalation and exhalation.

The respiration of birds is associated with the activity of large air sacs, which are combined with the lungs and pneumatic bones.

Birds have 9 main air sacs - 4 paired, located symmetrically on both sides, and one unpaired. The largest are the abdominal air sacs. In addition to these air sacs, there are also air sacs located near the tail, the posterior trunk, or intermediate.

Air sacs are thin-walled formations filled with air; their mucous membrane is lined with ciliated epithelium. From some air sacs there are processes leading to bones that have air cavities. There is a network of capillaries in the wall of the air sacs.

Air sacs perform a number of roles:

1) participate in gas exchange;

2) lighten body weight;

3) ensure normal body position during flight;

4) help cool the body during flight;

5) serve as an air reservoir;

6) act as a shock absorber for internal organs.

Pneumatic bones in birds are the cervical and dorsal bones, caudal vertebrae, humerus, thoracic and sacral bones, and the vertebral ends of the ribs.

The lung capacity of chickens is 13 cm 3, ducks - 20 cm 3, the total capacity of the lungs and air sacs is 160...170 cm 3, respectively, 315 cm 3, 12...15% of it is the tidal volume of air.

Functional features. Birds, like insects, exhale when the respiratory muscles contract; In mammals, the opposite is true - when the inspiratory muscles contract, they inhale.

Birds have relatively frequent breathing: chickens - 18...25 times per minute, ducks - 20...40, geese - 20...40, turkeys - 15...20 times per minute. The respiratory system in birds has great functionality - under load, the number of respiratory movements can increase: in farm birds up to 200 times per minute.

The air entering the body during inhalation fills the lungs and air sacs. Air spaces are actually reserve containers for fresh air. In the air sacs, due to the small number of blood vessels, oxygen absorption is negligible; In general, the air in the bags is saturated with oxygen.

In birds, the so-called double gas exchange occurs in the lung tissue, which occurs during inhalation and exhalation. Due to this, inhalation and exhalation are accompanied by the extraction of oxygen from the air and the release of carbon dioxide.

In general, breathing in birds occurs as follows.

The muscles of the chest wall contract so that the sternum is raised. This means that the chest cavity becomes smaller and the lungs are compressed to the point that carbon dioxide-laden air is forced out of the breathing chambers.

As air leaves the lungs during exhalation, new air from the air spaces moves forward through the lungs. When you exhale, air passes predominantly through the ventral bronchi.

After the muscles of the chest have contracted, exhalation has taken place and all used air has been removed, the muscles relax, the sternum moves down, the chest cavity expands, becomes large, a difference in air pressure is created between the external environment and the lungs, and inhalation is carried out. It is accompanied by air movement mainly through the dorsal bronchi.

The air sacs are elastic, like the lungs, so when the chest cavity expands, they also expand. The elasticity of the air sacs and lungs allows air to enter the respiratory system.

Since muscle relaxation causes air to enter the lungs from the environment, the lungs of a dead bird, whose breathing muscles are normally relaxed, will be distended, or filled with air. In dead mammals they are asleep.

Some diving birds can remain underwater for a significant period of time, during which air circulates between the lungs and air sacs, and most of the oxygen passes into the blood, maintaining an optimal oxygen concentration.

Birds are very sensitive to carbon dioxide and react differently to increases in its content in the air. The maximum permissible increase is no more than 0.2%. Exceeding this level causes inhibition of respiration, which is accompanied by hypoxia - a decrease in the oxygen content in the blood, while the productivity and natural resistance of birds decreases. In flight, breathing is reduced due to improved ventilation of the lungs even at an altitude of 3000...400 m: in conditions of low oxygen content, birds provide themselves with oxygen by breathing rarely. On the ground, birds die under these conditions.

Birds is unique. In birds, air flows go only in one direction, which is not typical for other vertebrates. How can you inhale and exhale through one trachea? The solution is an amazing combination of unique anatomical features and manipulation of atmospheric flow. The peculiarities of the respiratory system of birds determine the complex mechanisms of the air sacs. They are not present in mammals.

Bird respiratory system: diagram

The process in winged birds is carried out somewhat differently than in mammals. In addition to lungs, they also have air sacs. Depending on the species, the respiratory system of birds may include seven or nine of these lobes, which extend into the humerus, femur, vertebrae, and even the skull. Due to the absence of a diaphragm, air moves by changing the pressure in the air sacs using the pectoral muscles. This creates negative pressure in the blades, forcing air into the breathing system. Such actions are not passive. They require certain muscle contractions to increase pressure on the air sacs and push the air out.

The structure of the respiratory system of birds involves raising the sternum during the process. The lungs of birds do not expand or contract like the organs of mammals. In animals, oxygen exchange occurs in microscopic sacs called alveoli. In winged relatives, gas exchange occurs within the walls of microscopic tubes called air capillaries. birds work more efficiently than mammals. They are able to carry more oxygen with each breath. When compared to animals of similar weight, there are slower breathing rates.

How do birds breathe?

Birds have three different sets of respiratory organs. These are the anterior air sacs, lung sacs and posterior air sacs. During the first breath, oxygen passes through the nostrils at the junction between the top of the beak and the head. Here it is heated, moistened and filtered. The fleshy tissue that surrounds them is called a cere in some species. The flow then moves into the nasal cavity. The inhaled air goes further down into the trachea, or windpipe, which divides into two bronchi. They then branch into many pathways in each lung.

Most of the tissue of this organ consists of about 1800 small adjacent tertiary bronchi. They lead into tiny air capillaries that intertwine with blood capillaries, where gases are exchanged. The air flow does not go directly to the lungs. Instead, it follows the caudal saccules. A small amount passes through the tail formations through the bronchi, which in turn are divided into smaller capillaries. When the bird inhales a second time, oxygen moves into the cranial air sacs and back out through the fistula into the trachea through the larynx. And finally, through the nasal cavity and out of the nostrils.

A complex system

The respiratory system of birds consists of paired lungs. They contain static structures on the surface for gas exchange. Only the air sacs expand and contract, forcing oxygen to move through the motionless lungs. The inhaled air remains in the system for two complete cycles before it is completely consumed. Which part of the bird's respiratory system is responsible for gas exchange? The lungs play this important role. The air spent there begins to leave the body through the trachea. During the first inhalation, waste gases pass into the anterior air sacs.

They cannot immediately leave the body, since during the second inhalation fresh air again enters both posterior sacs and the lungs. Then, during the second exhalation, the first flow flows out through the trachea and fresh oxygen from the posterior sacs enters the organs for gas exchange. The structure of the respiratory system of birds has a structure that allows for the creation of a unidirectional (one-way) influx of fresh air above the surface of the ongoing gas exchange in the lungs. Moreover, this flow passes there during both inhalation and exhalation. As a result, the exchange of oxygen and carbon dioxide occurs continuously.

System efficiency

The peculiarities of the respiratory system of birds make it possible to obtain the amount of oxygen necessary for the cells of the body. The big advantage is the unidirectional nature and structure of the bronchi. Here the air capillaries have a larger total surface area than, for example, in mammals. The higher this number is, the more oxygen and carbon dioxide can circulate in the blood and tissues, allowing for more efficient breathing.

Structure and anatomy of the air sacs

The bird has several sets of air tanks, including caudal abdominal and caudal pectoral. The cranial sacs include the cervical, clavicular and cranial thoracic sacs. Their contraction or expansion occurs when the part of the body in which they are located changes. The size of the cavity is controlled by muscle movement. The largest air reservoir is located inside the peritoneal wall and surrounds the organs located in it. In an active state, for example during flight, the bird requires more oxygen. The ability to compress and expand body cavities allows not only to move more air through the lungs faster, but also to lighten the weight of the feathered creature.

During flight, the rapid movement of the wings creates an atmospheric flow that fills the air sacs. The abdominal muscles are largely responsible for the process while at rest. The respiratory system of birds differs both structurally and functionally from that of mammals. Birds have lungs - small, compact, spongy structures formed among the ribs on either side of the spine in the chest cavity. The dense tissues of these winged organs weigh the same as in mammals of equal body weight, but occupy only half the volume. Healthy individuals usually have light pink lungs.

Singing

The functions of the respiratory system of birds are not limited to just breathing and oxygenating body cells. This also includes singing, with the help of which communication between individuals occurs. A whistle is a sound produced by the vocal organ located at the base of the trachea. As with the mammalian larynx, it is produced by the vibration of air flowing through the organ. This peculiar property allows some species of birds to produce extremely complex vocalizations, even imitating human speech. Some song species can produce many different sounds.

Stages of breathing cycles

The inhaled air passes through two respiratory cycles. Taken together, they consist of four stages. A series of several interrelated steps maximizes the contact of fresh air with the respiratory surface of the lungs. The process goes like this:

1. Most of the air inhaled during the first step passes through the primary bronchi into the posterior air lobes.
2. Inhaled oxygen moves from the posterior sacs to the lungs. This is where gas exchange occurs.
3. The next time the bird inhales, the oxygenated stream moves from the lungs to the front chambers.
4. The second exhalation forces carbon dioxide-rich air from the anterior sacs through the bronchi and trachea back into the atmosphere.

High oxygen demand

Due to the high metabolic rate required for flight, there is always a high demand for oxygen. Considering in detail what kind of respiratory system birds have, we can conclude: the features of its structure quite help to satisfy this need. Although birds have lungs, they rely primarily on air sacs for ventilation, which make up 15% of their total body volume. At the same time, their walls do not have a good blood supply, and therefore do not play a direct role in gas exchange. They act as messengers to move air through the respiratory system.

Winged birds lack a diaphragm. Therefore, instead of regular expansion and contraction of the respiratory organs, as is observed in mammals, the active phase in birds is exhalation, which requires muscle contraction. There are various theories about how birds breathe. Many scientists are still studying the process. The structural features of the respiratory systems of birds and mammals do not always coincide. These differences allow our winged cousins ​​to have the necessary adaptations for flight and singing. It is also a necessary adaptation to maintain high metabolic rates for all flying creatures.