Chicken Lungs

Anyone who knows me knows of my hate-hate relationship with running.  I have started running in the past year, and have decided that it is the most ridiculous activity known to man.  You can’t score goals, you can’t look cool, and you will NEVER make it to Sportcenter (Usain Bolt excluded….I mean….he IS Usain Bolt).

The main reason I hate running is because I suck at it.  I’m strong, but my aerobic capacity is lousy.  I wish I was a bird.  If I was a bird, my trachea (windpipe) would be 2.7 times as large, reducing air resistance.  My rate of breathing would be about 1/3 of what it is currently, and I would take much bigger breaths.  This is the first part of the system that makes the bird respiratory system much more efficient at gas exchange than mammals (especially this particular mammal).

chicken airsacs

Location of Air Sacs in a hen

Chickens also have structures called air sacs.  The way to think of them are a bit like bagpipes…..they act as reservoirs for air so that there is constantly fresh air passing through the hens lungs.  A bird’s respiratory cycle is much more complicated than ours….we inhale into a big, complicated balloon, pause, and then push the air out.  As the air sits in the tiny air sacs (called alveoli), oxygen diffuses into the blood, and CO2 diffuses out.   Our alveoli are like a bunch of grapes….blind ended sacs that expand and contract as air comes in and out.  During the pause between breaths, the oxygen concentrations of the gasses change, and diffusion becomes slower. In hens, it goes like this….INHALE – air goes into the lungs and the abdominal air sacs.  EXHALE – air leaves the cranial, clavicular and cervical air sacs.  PAUSE – air goes from lungs to front air sacs while air is travelling from abdominal air sacs to the lungs.  Repeat as necessary.The result of these airbags is that there is a constant, one way flow through the lungs, and every part of the lung is constantly filled with fresh, fully oxygenated air.  Chickens have no alveoli…they have a network of tiny tubes where the air never stops flowing.

Diagram of airflow....not simple, but effecive

Diagram of airflow….not simple, but effecive

Hens have other adaptations too.  Birds have hollow bones, and the front air sacs communicate with the wing bones and the clavicles.  Thus, chickens even use their bones to breathe!  At the microscopic level, the point at which the oxygen enters the blood (and CO2 leaves it) is different too.  Cross current exchange where blood travels at 90 degrees to the airflow in the tiny lung tubes….makes for much more efficient exchange because the same air crosses blood vessels several times, instead of just once as in us mammals.  Also, the thickness of the tissues between the blood and the air is less than half that in mammals of similar sizes.Chickens have no diaphragm, which is the muscle we use to expand our chest cavity downwards.  This has major implications if you are handling chickens, especially small ones.  Their keel bone (Breast bone) MUST be able to move, or they can’t inhale.  Holding or wrapping a chicken  too tightly will stop her from breathing.  This is really important when children are around the hens, since a hug that would work for Fido will not work for chickens.So, in summary…birds breathe slower, deeper and more efficiently.  They have one way flow of air through their lungs through the adaptation of air sacs that act as bellows to constantly supply fresh air to the blood, even when the hen is not inhaling.This is why birds have such an efficient respiratory system, and why aerobic exercise is so much easier for them.When I am about 2 miles into a run, I really hate chickens. Mike the Chicken Vet

7 responses to “Chicken Lungs

  1. Hi Dr. Petrik,

    This post couldn’t have come at a better time!
    In biology class today we learnt all about the human respiratory system (and my teacher even talked about the birds respiratory system)!

    I am going to send him a link to this.

    Thanks for sharing your knowledge, appreciated as always.


    • Hey Andrew….glad the timing worked out so well! I’m always fascinated by the different ways that different animals solve physiological problems…..and usually haw much better they do at it than humans do!

  2. Is this why birds in general are more susceptible to respiritory pollutants? Like the canary in the coal mine?

    • Partly, John. The way the bird’s anatomy is set up, many contaminants end up settling in the abdominal air sacs , and that is where many infections occur. Another factor is bird’s high metabolic rates. Any toxin will affect them first ( and the smaller the bird, the faster the metabolism…..hence the canary instead of the turkey in the coal mine) because of their faster incorporation into their systems.


  3. I have two Arakana chickens one rooster and one hen. When I got them, the owner told e they were pure bred arakanas. My mum wanted them because arakanas lay green eggs. Ours aren’t.
    Excuse my spelling!

  4. Do you know why they are not laying green eggs?

    plz rply

    • Hi Marilyn….sorry for the slow response. From what I was able to find out, the hens must not be auracanas. There is a lot of misconceptions about this relatively rare breed, and many people sell hens as Americaunas, which are not necessarily the same thing. Auracanas lay green eggs, as do “olive eggers”, which are mixed breed hens. As far as I know, you cannot make auracanas lay eggs that are not green, and you cannot make others lay green eggs….the shell colour is genetic. My guess is that the hens you have are not actually auracanas.


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