Why are tears sore? – Aarna, age 6
Hi Aarna, thanks for your big question! I’m going to start by telling you a little story about sea turtles. That might sound weird, but don’t worry, it will all make sense soon.
When mother turtles slip on the beach at night to lay their eggs, if you look carefully you may see them shedding a few tears. There is an old myth that mother turtles cry because they can never meet their babies.
But scientists have found that sea turtles do not cry. Instead, they get rid of salt from their bodies, through crying tears of salt.
Read more: Curious Kids: Why do tears come to our eyes when we cry?
Because sea turtles live in salt sea water, and their favorite is the sea, (which is mostly made with sea water!) They build up too much salt in their bodies , which may be toxic. So they have to “cry” this salt out of their bodies to survive.
If we eat too much salt or it builds up in our bodies, our kidneys help to flush out when we go to the toilet. But sea turtle kidneys are not as smart as human kidneys, and they can’t get rid of enough salt in their small weeks.
Thus, sea turtles have a specific salt gland in each eye, which is twice the size of their brains, which pumps this extra salt into tears.
Those turtle tears are so painful, some animals like butterflies have been seen tearing up those turtle tears.
But what about us humans?
If you’re ever tearing tears coming down your cheek, it might taste a little salty. But if our kidneys work better than turtles’, and we don’t eat slippery for breakfast, why are our tears still salty?
Well, every liquid in our bodies contains a little salt. This salt is made electrically to help our muscles contract and our brains to think. The amount of salt in our body (such as tears, sweat, and saliva) is about the same as the level of salt in our blood – just under 1%, or about two teaspoons of salt per liter.
So our tears are much saltier than the tears of sea turtles, although they are still a little salty.
Read more: Curious Kids: how do sea creatures drink seawater and not get sick?
3 types of tears
The salinity of your tears can really change depending on the type of tear your eyes are making.
That’s right, make your eyes – or part of your eyes called the lacrimal gland, to be precise – three different types of tears. These are called basal tears, reflex tears and emotional tears.
basal tears keep your eyes wet and stop leg germs attacking your eyes
tears reflex made when your eyes need to wash away something that comes in, such as smoke or grains of sand
emotional tears is the kind you cry when you feel very happy or sad.
They contain more salt than basal tears and reflex tears than emotional tears, which are important for keeping your eyes healthy. Emotional tears involve more than just other things, including a hormone (a specific type of chemical in your body) that acts as a natural breaker. This may help explain why we sometimes feel better after a good cry.
Read more: Curious Kids: why do we cry?
The next time you shed a few salty tears, take a moment to think about how lucky you are to have kidneys that control the salt levels in your body, and you don’t have to have sore tears to survive. , like those mother turtles.
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