• Question: Why is it that the red blood cells in chicken's have a nucleus and no other animal does?

    Asked by livviemstevens to Judith on 15 Jun 2012.
    • Photo: Judith Sleeman

      Judith Sleeman answered on 15 Jun 2012:

      Actually, it’s not just chickens: sorry if I misled you! All birds (and reptiles) have red blood cells that keep the nucleus. Other warm blooded animals have red blood cells that lose their nuclei as they specialise into red blood cells. It’s thought to be because birds have taken a slightly different pathway as they’ve evolved.

      There are different theories about why this has happened and no-one really knows for sure. Popular ones are:

      We have extremely narrow blood vessels, called capillaries, in our tissues and organs where the blood supplies oxygen and nutrients. If our red blood cells had a nucleus, they wouldn’t be able to squeeze through. Birds have slightly wider blood vessels.

      Or maybe..

      Getting rid of the nucleus means that the whole of the cell is cytoplasm and can be filled up with haemaglobin to carry more oxygen per cell. So our hearts don’t have to work so hard. Have you ever held a bird and felt how fast their hearts beat?

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