Air sacs of pigeon are 9 in number that are located in various parts of their body, including their head, neck, chest, and abdomen.
What are the air sacs in birds?
The air-sacs are bladder-like structures that are formed by the dilation of the mucous membrane of the bronchus to help the bird in respiration. Pigeons, like many birds, have air sacs in their respiratory system. These air sacs are thin-walled, balloon-like structures that are connected to the lungs and help to move air through the respiratory system. These air sacs are located in various parts of the body, including the chest, neck, and head. The air sacs serve several important functions in the bird’s respiratory system. They help to bring fresh air into the lungs and remove waste gases, and they also help to regulate the temperature of the air in the respiratory system. In addition, the air sacs help to lighten the weight of the bird’s body, which is important for flight. Birds have nine air sacs.
Types of Air Sacs of Pigeon
Pigeons have nine air sacs and they are as follows.
Fig: Air sacs of pigeons (birds).
1. Interclavicular
- It is a single median air sac and triangular in shape.
- It is a large air sac.
- It is connected to both lungs.
- It is located between the two limbs of the furcula.
- On either side, it gives off an axillary or extra-clavicular sac in the armpit, communicating with an air cavity of the humerus, and a clavicular sac.
2. Cervical
- These are paired air sacs which means they are two in number.
- They arise anteriorly, one from each lung.
- They are located at the base of the neck, dorsal to the interclavicular air sac, and alongside the vertebral column.
- They give off minor saccules at the neck.
- These sacs send diverticula into the cervical vertebrae and the skull.
3. Anterior Thoracic
- These are paired air sacs.
- They are present ventral to the lungs in the anterior part of the chest, in close contact with the ribs and the pericardium.
- They extend back as if they overlap the posterior thoracic air sacs.
4. Posterior Thoracic
- These are paired air sacs.
- The left sac is slightly larger than the right.
- They are found in the posterior part of the thoracic cavity, just anterior to the abdominal air sac.
- Each sac overlaps the posterior end of its lung.
5. Abdominal
- These air sacs are also called posterior air sacs.
- They arise from the outer posterior angle of each lung.
- They are located along the dorsal wall of the abdomen, ventral to the kidneys, and amongst the coils of the small intestine.
- These are the posteriormost and largest air-sacs in birds.
- The right air sac is larger than its left.
So, all the nine air sacs of pigeon (also birds) are : (interclavicular 1 + cervical 2 + anterior thoracic 2 + posterior thoracic 2 + abdominal 2) = 9
Functions of Air Sacs of Pigeon / Birds
1. Lightness :
- These air sacs probably act as balloons to provide lightness and buoyancy to the body.
- Although this view is no longer supported now.
2. Flight :
- They help in flight.
- The best fliers among birds possess the most highly developed air sacs.
3. Accessory respiratory organs :
- The sacs function principally as accessory breathing organs.
- Their smooth lining is devoid of capillaries and does not take part in gaseous exchange.
- They serve as reservoirs and take part in the movements of air during respiration.
4. Temperature regulation :
- As the skin of birds lacks integumentary glands, their skin has no utility in the regulation and maintenance of body temperature.
- The air sacs may also help as cooling devices in the regulation of the temperature of the body by the retention of warm moist air inside the air- sacs.
- They compensate for the lack of sweat glands.
5. Cardiac movements :
- Another probable function of air sacs, according to Muller (1908), appears to allow for the movement of the heart in an otherwise very rigid thorax.
6. Balancing :
- Air sacs are arranged perfectly on the two sides of the body so that the proper center of gravity is maintained for the flight.
- If somehow the equilibrium is altered, it is restored by shifting the contained air from one side of the body to another.
7. Minimized mechanical friction :
- Air sacs and their bronchus are inserted between muscles like pads which reduces mechanical friction during flight.
8. Resonator :
- Air sacs help in the forceful expulsion of air and control the pitch of sound thus, act as resonators.
9. Regulate the moisture content of air :
- The walls of the air- sacs evaporate water and thus regulate the moisture content of the air.
10. Serve as the containers of reserve air :
- During the flight, the respiratory process is slightly hampered for a time. Therefore, some internal source of the reservoir of air is needed.
- The air-sacs serve this function and ventilate the lungs during flight.
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