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Write an article | Seven Jun

This year is the year of the Rabbit. I wish you all a happy year of the Rabbit!

Is there any cold knowledge that ordinary people don't know about rabbits as an ordinary animal?

You may not know that rabbits actually have a special pain point, that is, eating is not delicious, stuffy nose will die. It was the same when you were born, but you don't remember.

(photo Source: Internet) what's going on here?

For us humans, although it is uncomfortable when the nose is stuffy, we can breathe through the mouth. If you are not angry enough when running, you can also use your mouth.

But rabbits can't. In fact, most mammals can breathe through their mouths, but rabbits are an exception. Rabbits can only breathe through their noses.

Therefore, if the rabbit's nasal cavity is blocked, such as a runny nose, ear infection or booger in the nose, they will have difficulty breathing and may even be suffocated alive. This is why respiratory diseases are the main cause of rabbit death.

This animal that must breathe through the nose is called an obligatory nasal breathing animal (obligate nasal breathers). In addition to rabbits, there are a few mammals that cannot breathe through their mouths, including rodents and horses.

(photo Source: Internet) but why can't rabbits breathe through their mouths?

In short, there is no connection between their mouths and lungs.

Specifically, the rabbit's mouth and nasal cavity are separated by the hard palate (equivalent to the top of the human mouth) and the soft palate (equivalent to the back of the human mouth), as well as the epiglottis (the lid at the end of the mouth), and the upper respiratory tract does not intersect with the esophagus. It's the same with horses.

The rabbit's epiglottis (epiglottis) and soft palate (soft palate) can completely seal the mouth. The trachea is the left tube and the esophagus is on the right. (photo: Sohn, Joanne, and Marcelo A. Couto. "Anatomy, physiology, and behavior." The laboratory rabbit, Guinea pig, hamster, and other rodents. Academic Press, 2012. 195-215.) of course, when there is no way, these animals can barely take two breaths with their mouths. It's just that the channel between their mouth and lungs is very narrow, so it's very inefficient to breathe through their mouths, and they can easily "lose their breath".

So why are there animals that can only breathe through their noses?

One theory is that this may be a property peculiar to animals with a very strong sense of smell.

Things start with the lid of the mouth, the epiglottis.

Human epiglottis (black refers to) and trachea (lower arrow) (photo: wikipedia) many people believe that the function of the epiglottis is the lid of the throat to prevent food from flowing into the trachea. Epiglottis does have this effect in humans, but there are some phenomena that contradict this view.

In fact, people who lose their epiglottis due to lupus can swallow normally and food and water do not run into the trachea. And many animals do not have epiglottis, such as frogs, snakes, lizards, turtles, crocodiles and birds. Even in mammals, there is no epiglottis, such as sea lions. But these animals don't eat food into their lungs.

(photo source: Internet) the epiglottis is not there to make a sound, because there is no necessary connection between the epiglottis and the voice. For example, birds do not have epiglottis, but the vocal ability of birds is obvious to all. Sea lions and gibbons whose epiglottis are close to zero also make a variety of sounds.

As a result, V. E. Negus, an ear, nose and throat researcher at King's College Hospital in England, suggests that the most primitive function of epiglottis may be to help animals smell other environmental odors (such as predators) while eating. His evidence is that animals with a good sense of smell have a well-developed epiglottis, while animals with a poor sense of smell lack it. In other words, the epiglottis may be an auxiliary olfactory organ.

(photo source: wikimedia) herbivores like rabbits have limited vision when they bow their heads to dry food. In order to guard against predators, it is best not to let the smell of food rush into the nasal cavity, affecting judgment. To achieve this goal, growing a large epiglottis is one of the best solutions.

Negus points out that animals that lack epiglottis, such as birds and sea lions, lose their sense of smell when they open their mouths, so they cannot tell the smell of their enemies when they are cooking. However, the olfactory ability of these animals is not good, so it has little effect on survival.

By the same token, we are the same with those who have a keen vision but not a good sense of smell. Although humans also have epiglottis, it is underdeveloped, which is why we can smell food when we eat.

(photo source: wikimedia) Negus further pointed out that in order for the epiglottis to completely seal the mouth, the soft palate and nasal passages of animals with a good sense of smell need to be longer, like rabbits and horses. Conversely, humans who do not have a keen sense of smell have shorter snouts than these animals.

In short, this theory holds that a well-developed sense of smell needs to block the interference from the mouth gas, so the mouth is disconnected from the respiratory tract, and that keeping the mouth and respiratory tract from being connected requires a large epiglottis and the appearance of a car giant.

Car Giant (Photo: Attack on Titan) at this point, you might wonder how miserable it is not to smell the food when you eat.

In fact, you also had this kind of debuff ability when you were a child, but you just don't remember it.

The researchers found that although mature humans are not exclusive nose-breathing animals, human cubs are.

Human newborns, like rabbits, have relatively independent esophagus and respiratory tract and cannot breathe through their mouths. They can only breathe through their mouths when they are a few months old. In fact, the newborns of all mammals are specialized nose-breathing animals.

(photo source: watermark) obviously, this is because mammals need to be fed at birth, and the separation of the esophagus and respiratory tract ensures that they breathe while drinking milk.

Specific nasal breathing also gives human newborns a different physiological structure from adults.

Compared with adults (right), infants (left)'s epiglottis (gray area referred to by epiglottis) and soft palate (grey area referred to by soft palate) form tight oral seals, just like rabbits. (photo Source: (DOI) 10.3389 / fped.2015.00052) for example, the throats of newly unloaded human cubs are as high as those of animals that can only breathe through their noses, at the position of cervical vertebrae 3-4, but the throats of adults sink to cervical vertebrae 6-7.

In addition, the epiglottis is harder in newborns than in adults. So when a human cub stretches its head too hard, it may clog its respiratory tract. Stretch your neck and wait for that kind of action, which only a mature person can do.

In short, the food of Bizi Ling is not delicious, and nature is really strange. And everyone used to eat and breathe like a rabbit. No one can keep the memory of "tasteless food", which can be regarded as a kind of happiness.

Reference:

Https://docs.qq.com/doc/DVG9tendiWkhLRXpX

This article is from the official Wechat account: bring Science Home (ID:steamforkids), author: everything.

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