Science in your tasty cup

Dr. Wendy Sue Universe

Dr. Universe,

Why do we get tears when we yawn?

— Ella, 8, Australia

A lot of people get tears when they yawn. When you yawn, you actually use a lot of muscles in your face. Maybe you can feel the stretch in your jaw, cheeks and eyes.

As the muscles in your face contract, they can put a lot of pressure on the plumbing system that is in charge of making your tears.

That’s what I found out from my friend, Karin Biggs, an adjunct professor at Washington State University who teaches anatomy.

She told me that we have two little almond-shaped structures called the tear glands, or the lacrimal glands, that produce our tears. These glands are located up near the eyelids, and it is likely they are making tears at this very moment.

“Tears are made all the time,” Biggs said. “They are responsible for keeping our eyes moist, helping us see and keeping our eyes healthy.”

Meanwhile, there are also two tiny tubes located near the inside corner of your eyes. These tubes, or lacrimal canals, are where the tears can exit your eyes as you yawn.

Like a very slow faucet, the teary fluid is constantly being released from the gland. Gravity pulls the fluid down and around the eye. You might think of it like putting a ball in your bathroom sink then running the water faucet over it. The faucet is your gland, the drain is where tears exit and the ball is the eye.

“When we yawn we are contracting all the muscles in our face,” Biggs said. “We are just squeezing the tears out of the gland and out of the tubes because we have squeezed all of our face at once.”

Biggs also told me there are 43 muscles in the human face. You may squish up a lot of those face muscles when you sneeze or laugh, too.

The muscles in our bodies can help us do all kinds of things. Biggs told me there are even some muscles people have that other people seem to be missing. The plantaris muscle in the knee is one of them. Only about 10 percent of people do not have this muscle, but they usually seem to be fine without it.

But tear ducts and tear glands in our eyes are among the many body parts that humans have in common. This plumbing system helps you create, transport and drain all your tears.

The ability to make tears is all a part of the human experience. But other animals like cats and elephants can make tears, too. Tears are mostly water with some other ingredients that help keep our eyes in good shape.

Whether your tears come from crying, sneezing, laughing or yawning, they are often a good sign your body is taking care of you and that your eyes are working well.

Have a science question? Ask Dr. Wendy Sue Universe, WSU’s resident science cat and writer, by email at Dr.Universe@wsu.edu.

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