The hardest parts of the body are actually the teeth. (If you want to be crooked, give me a thumbs up!)
More precisely, it is the outermost layer of the enamel of the tooth, about 2-2.5mm thick and translucent.
（Photo source veer）
According to the Mohs scale (the higher the number, the harder it is), the hardness of tooth enamel is 6~7, and the hardness of iron is 4~5, that is, tooth is harder than iron Still tough!
Are you surprised? Are you surprised? Don’t worry, Xiaohong has also prepared 10 human body cold knowledge, which will definitely allow you to get new knowledge~
Saliva is bacteria and urine is sterile
Strictly speaking, saliva and urine produced by the human body under normal conditions are sterile.
It’s just that saliva mixes with sloughed mucosal epithelial cells, white blood cells, bacteria, and food debris in the mouth to become mixed saliva or whole saliva, which is what we call Known saliva.
Of course, there are bacteria in the urethra, and urine excreted through the urethra can also be contaminated with bacteria, but midstream urine is usually sterile.
It’s like a rusty faucet. The water that flows out at the beginning washes away the rust, and the water behind is free of rust? This is also the reason why the hospital does a urine test and asks to stay in the middle part of the urine.
Children have more bones than adults
Because a child’s bones are not fully developed, some of the bones will fuse together as they grow.
For example, the coccyx of a newborn child has 4~5 pieces, which will gradually fuse into one piece, and there are 206 bones in total when it finally matures.
So children will have more bones than adults.
Skins have memory
For example, a rash and itching on the forearm after sun exposure this year may the same symptoms in the same place after sun exposure next year.
Additionally, research has found that inflammation induced after skin damage (wound or infection) leaves a long-term memory in epithelial stem cells and accelerates skin healing when inflammation reappears.< /strong>.
Only humans have jaws
From the skull, only Homo sapiens (that is, us modern humans) have jaws, other hominids and even orangutans do not.
As for why we humans evolved a chin, some people speculate that it was in evolution that the face became smaller, so the chin was protruded; some people speculated that it was for >Chewing, there are different opinions, and there is no conclusion for the time being.
Liver can regenerate
Under normal conditions, human liver cells are very long-lived.
But after liver damage, especially after most of the liver (2/3) has been removed, if the remaining liver is not inflamed and fibrotic, hepatocytes will Rapidly divide and proliferate, and can accurately control its own size.
It’s like pasting and copying, pasting the previous shape and size, and copying it back in about half a year.
Boys have thicker skin than girls
Studies have shown that men’s stratum corneum and dermis are thicker than women’s at all ages.
Because men’s dermis contains more water, matrix, and elastic fibers than women’s, all of which help increase skin thickness.
Interestingly, men’s skin thickness begins at age 20 and gradually thins with age, while women’s skin stays the same, beginning to whizz after age 50 Rapid decline, signs of aging are also visible to the naked eye.
This is the reason why some girls spend a lot of money to buy skin care products to smash their faces, but the effect is not as good as that of boyfriends who don’t take care of their skin very much.
The nose usually has only one nostril for ventilation
Put your fingers under both nostrils and breathe normally. You will find that the airflow in one nostril is large, and the airflow in one nostril is almost nonexistent.
Our nasal cavity has upper, middle and lower turbinates, both on the left and right.
Normally the turbinate in one nasal cavity is congested and swollen and the other narrowed, so that one nostril is more ventilated and one less ventilated.
Take turns on both sides, usually every 2-7 hours. This process is called the nasal cycle.
The eyes are the least afraid of cold
We feel cold because there are heat and cold receptors on the surface of the skin.
Although the cornea, conjunctiva, and sclera of the eye are rich in tactile and pain nerves, there are no heat and cold receptors.
Therefore, the eyes do not feel cold, nor do they feel hot.
There are more bacteria in the mouth than there are people on earth
The mouth is always warm and humid, coupled with slightly alkaline saliva, perfect for bacteria to survive.
Normally, there are approximately 50 billion bacteria in a person’s mouth. If you don’t pay attention to oral hygiene and food scraps provide nutrients to bacteria, the number of bacteria that multiply can at least double, that is, 100 billion.
The 2022 World Population Prospects published by the United Nations Department of Economic and Social Affairs predicts that the global population will reach 8 billion by November 15, 2022, Compared with the bacteria in the mouth, it is really nothing.
The skin is the largest organ in the human body
Unexpectedly, the skin is not only an organ, but also the largest organ of the human body.
From the perspective of weight and area, skin accounts for about 16% of body weight, and the area varies according to height, short, fat and thin, and adults are generally 1.5~ 2m².
In addition, the skin has functions such as barrier, thermoregulation, sensory, secretion and excretion, absorption, immunity, and is a very important and largest organ of the human body.
Okay, that’s all for today’s sharing. Is there any cold knowledge that refreshes you?
Solo Lele is not as good as crowd Lele, such an interesting cold knowledge of the human body, it is better to share with friends so that they can also increase their knowledge!
[Referencesoffer]
[1] Zhao Bian, editor-in-chief. Chinese Clinical Dermatology 2nd Edition [M]. Nanjing: Jiangsu Science and Technology Press, 2017.04.
[2] Li Jiji, Zeng Yuanshan, etc. Histology and Embryology 9th Edition [M]. Beijing: People’s Health Publishing House. 2018.08.
[3] Naik, S., Larsen, S., Gomez, N. et al. Inflammatory memory sensitizes skin epithelial stem cells to tissue damage. Nature 550, 475–480 (2017) .