The respiratory system of birds is unique. In birds, air flows in only one direction, which is not characteristic of other vertebrates. How can one breathe in and out through one trachea? The solution is an amazing combination of unique anatomical features and manipulations of the atmospheric flow. Features of the respiratory system of birds determine the complex mechanisms of air sacs. They are not present in mammals.
Respiratory system of birds: scheme
The process in winged is somewhat different than in mammals. In addition to the lungs, they also have air bags. Depending on the species, the respiratory system of birds may include seven or nine of these lobes, which have access to the humerus and femur, vertebrae and even the skull. Due to the lack of a diaphragm, air moves by changing the pressure in the air sacs with the help of the pectoral muscles. This creates negative pressure in the blades, causing air to enter the respiratory system. Such actions are not passive. They require certain muscle contractions to increase pressure on the air sacs and push air out.
The structure of the respiratory system of birds involves raising the sternum during the process. Feathered lungs do not expand or contract like mammalian organs. In animals, the exchange of oxygen and carbon dioxide occurs in microscopic sacs called alveoli. In winged relatives, gas exchange is carried out in the walls of microscopic tubes, called air capillaries. The respiratory organs of birds work more efficiently than in mammals. They are able to carry more oxygen with each breath. When compared with animals of similar weight, there are slower respiratory rates.
How do the birds breathe?
Birds have three different sets of respiratory organs. These are front air bags, light and rear air bags. During the first breath, oxygen passes through the nostrils at the junction between the top of the beak and head. Here it is heated, moistened and filtered. The fleshy tissue that surrounds them is called waxen in some species. Then the flow moves into the nasal cavity. The inhaled air goes further down into the trachea, or the respiratory throat, which is divided into two bronchi. Further, they fork into many paths in each lung.
Most of the tissue of this organ is about 1800 small adjacent tertiary bronchi. They lead into tiny air capillaries that intertwine with blood capillaries, where gas is exchanged. The air flow does not go directly to the lungs. Instead, it follows in caudal sacs. A small amount passes through the caudal masses through the bronchi, which, in turn, are divided into smaller capillaries in diameter. When the bird inhales for the second time, oxygen moves into the cranial air sacs and then exits through the fistula into the trachea through the larynx. And finally, through the nasal cavity and leaves 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, causing oxygen to move through the motionless lungs. Inhaled air remains in the system for two full cycles before it is completely used up. What part of the respiratory system of birds is responsible for gas exchange? This important role is played by the lungs. The air exhausted there begins to leave the body through the trachea. During the first breath, the exhaust gases pass into the front air sacs.
They cannot immediately leave the body, as during the second breath, fresh air again enters both the rear bags and the lungs. Then, during the second exhalation, the first stream flows outward through the trachea, and fresh oxygen from the back sacs enters the organs for gas exchange. The structure of the respiratory system of birds has a structure that allows you to create a unidirectional (one-sided) flow of fresh air above the surface of the ongoing gas exchange in the lungs. In addition, this flow passes there during both inhalation and exhalation. As a result, the exchange of oxygen and carbon dioxide is carried out continuously.
System performance
Features of the respiratory system of birds allow you to get the amount of oxygen needed for body cells. The big advantage is the unidirectional nature and structure of the bronchi. Here, air capillaries have a larger total surface area than, for example, in mammals. The more this indicator is, the more oxygen and carbon dioxide can circulate in the blood and tissues, which ensures more efficient breathing.
The structure and anatomy of air sacs
The bird has several sets of air tanks, including caudal caudal and caudal thoracic. The cranial structure includes the cervical, clavicular and cranial chest bags. Their contraction or expansion occurs when the part of the body in which they are placed changes. The size of the cavity is controlled by muscle movement. The largest air tank is located inside the wall of the peritoneum and surrounds the organs located in it. In the active state, for example during flight, the bird needs more oxygen. The ability to compress and expand the body cavities allows not only faster to drive more air through the lungs, but also to lighten the weight of the feathered creature.
During the flight, the frequent movement of the wings creates an atmospheric stream that fills the air sacs. The abdominal muscles are largely responsible for the process, being in a calm state. The respiratory system of birds differs both structurally and functionally from that inherent in mammals. Birds have light - small, compact spongy structures formed among ribs on both sides of the spine in the chest cavity. The dense tissues of these winged organs weigh as much as mammals of equal body weight, but occupy only half the volume. Healthy individuals, as a rule, have light pink colors.
Singing
The functions of the respiratory system of birds are not limited to breathing and oxygenation of body cells. This also includes singing, with the help of which there is communication between individuals. Whistling is the sound received by a vocal organ located at the base of the height of the trachea. As in the case of the larynx of mammals, it is produced by vibration of the air flowing through the organ. Such a peculiar property allows some species of birds to produce extremely complex vocalizations, even imitating human speech. Some song types can produce many different sounds.
Stages of breathing cycles
Inhaled air passes through two respiratory cycles. In their totality, they consist of four stages. A series of several interconnected steps maximizes the contact of fresh air with the respiratory surface of the lungs. The process is as follows:
- Most of the air inhaled in the first step passes through the primary bronchi into the posterior air lobes.
- Inhaled oxygen moves from the back sacs to the lungs. There is gas exchange.
- The next time the bird inhales, the oxygen-rich stream moves from the lungs to the front vessels.
- The second exhalation displaces the air enriched in carbon dioxide from the front 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 oxygen demand. Considering in detail what kind of respiratory system in birds, we can conclude: the features of its device completely help to satisfy this need. Although the birds have lungs, they rely mainly on air sacs for ventilation, which make up 15% of the total body volume. At the same time, their walls do not have good blood supply, therefore they do not play a direct role in gas exchange. They act as intermediaries for moving air through the respiratory system.
Winged have no 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 system of birds and mammals do not always coincide. These differences allow our winged brethren to have the necessary equipment for flying and singing. It is also a necessary adaptation to maintain a high metabolic rate for all flying creatures.