Why do people shed tears when they laugh? Common sense of the human body

Whenever we open and close our eyes, the tears on the surface of these eyes will be sucked into the sewer of tears, that is, the nasolacrimal ducts. This nasolacrimal duct is a thin, not-so-long tube and the only tube that allows tears to pass through the nasal cavity.

As long as we laugh, the pressure in the nasal cavity will increase, and tears cannot enter the nasal cavity through the nasolacrimal duct, and when we laugh, the eyelids will be tightly closed, and the tears will be pushed into the nasal cavity, so the tears can not enter, and they are constantly squeezed, so the accumulated tears have to flow out.

People cry when they cry, but they often laugh out loud when they talk about something very funny, or a very funny joke. What's going on?

There is a gland above the outside of our eyeball, called the tear gland, which is the organ that specifically produces tears. After the tears are made, they are sent to the eyelids through a small, thin channel, and the eyelids coat the entire eyeball. The first is to keep the eyeball moist, and the second is to keep the eyeball clean.

Usually, the amount of tears is always kept normal. When the eyelids blink, the tears are drained into the nasolacrimal ducts and into the nasal cavity. So the tears don't flow out of the eye sockets.

Human tears are secreted all the time, flowing on the surface of the eyeball. However, there is very little tears secreted and they flow along the surface of the eyeball and in the tiny spaces inside the eyelids, so you don't feel that the tears are flowing.

However, in the blink of an eye, the tears on the surface of these eyeballs are sucked into the nasolacrimal duct, the sewer of the tears. Don't underestimate this not-so-long tube, it's the only way for tears to reach your nose. The lacrimal glands constantly secrete tears, and the nasolacrimal ducts constantly excrete tears, so people usually do not shed tears.

When a person laughs, the muscles of the cheeks, tongue and throat tense and contract, and the pressure in the mouth and nose increases. As a result of the increased pressure in the nasal cavity, it will temporarily block the work of the nasolacrimal duct to excrete tears, and the tears cannot be discharged, and more and more tears accumulate in the eyes. There will be tears in his eyes, and finally he will burst out of his eyes and flow to his face.

When people are crying, the pressure in the nasal cavity increases, the nasolacrimal duct leading to the nasal cavity is blocked, and the tears can't flow, and the tears in the eye sockets become more and more, and they can't fit it, and finally they flow out of the eyes.

The same is true when people are laughing. On the one hand, the eyelids are closed very hard and the tears are squeezed; On the other hand, because the pressure of the nasal cavity blocked the nasolacrimal duct, the channel where the tear level was normal could not go through, so it had to be redirected and flowed outside the eyes.

In fact, the same is true when people cry, and when they yawn, sneeze, cough, vomit, and even hold their breath.

Because when people laugh, their mouths are wide open, and they exhale as much air as possible out of their bodies, in order to exhale carbon dioxide and inhale oxygen. With the act of laughing, a strong breath of air is exhaled from the mouth, and the muscles of the cheeks, tongue, and throat tense and contract, and the pressure in the mouth and nose increases.

The increased pressure in the nasal cavity temporarily blocks the nasolacrimal duct from excreting tears, resulting in tears flowing out of the eyelids that should be discharged from the lacrimal ducts. This is a normal physiological phenomenon.

People laugh when they're happy and shed tears when they're unhappy. And some people laugh and laugh and shed tears, why is that? I believe that many friends don't know much, so let's join me to understand why I laugh and cry.

Explanation 1: Laughing. At this time, the pressure in the sinus cavity will increase, and the tears of people with more developed tear glands will be squeezed out due to the increased pressure. It's the same thing that some people cry when they blow their noses.

Explanation 2: Tears are often secreted and flow on the surface of the eye all the time. Tears are usually secreted very little, and they flow into the nasolacrimal ducts along the surface of the eyeball, so it is difficult for us to notice.

But when people laugh loudly, on the one hand, their eyelids are desperately closed, squeezing tears into their noses; On the other hand, the pressure in the nasal cavity increases, and the flow of tears to the nasal cavity is blocked, and the tears cannot flow, and more and more tears accumulate in the eyes, and finally they finally overflow, pass through the eyelid margin, and flow to the face.

Explanation 3: When you are very happy, you are so excited that you laugh, or when you hear a very funny story and you can't laugh out loud, you will find yourself laughing with tears in your eyes. Tears are often secreted and flow on the surface of the eyeball all the time.

However, because there are very few tears secreted normally, and you walk in a regular manner along the surface of the eyeball, and the tiny space between the inside of the eyelids, you will not feel the tears flowing.

However, the moment you open and close your eyes, the tears on the surface of these eyes are sucked into the nasolacrimal ducts, the underground waterways of tears. Don't underestimate this not too long tube, but it's the only way for tears to reach your nose! When people laugh loudly, on the one hand, their eyelids are desperately closed, squeezing tears into their noses; On the other hand, the pressure in the nasal cavity increases, and the flow of tears to the nasal cavity is blocked, and the tears cannot flow, and more and more tears accumulate in the eyes, and finally they come out, pass through the eyelid margin, and flow to the face.

One is that when laughing, the facial muscles pull the tear ducts, resulting in tears; Another theory is that our eyes are "crying" all the time, but there is a thin tube in the eye that communicates with the nasal cavity, and the usual "tears" flow from here, just like a sewer, and when we laugh, the facial muscles squeeze the thin tube, so that the "tears" cannot flow away, so they flow out of the eye sockets, so we see "laughing tears".