What is the difference between the left and right structures of the human body?

The human body is symmetrical in appearance, but there are many asymmetries in the anatomical structure and function of internal tissues.

The first is the respiratory organs. The trachea is divided into left and right main bronchi at the hilum, which enter the left and right lungs respectively, but the length, thickness and trend of the left and right main bronchi are quite different: the left bronchus is slender, about 4 ~ 5 cm long, with a horizontal direction and a small angle with the trachea; The right main bronchus is short and thick, about 3 cm long, with a relatively vertical direction and a large angle with the trachea. Because of this anatomical feature, foreign bodies in trachea often fall into the right main bronchus in clinic. The respiratory organs are not only anatomically asymmetric in the left and right main bronchi, but also anatomically asymmetric in the left and right lungs. For example, the left lung has only one oblique fissure, and the left lung is divided into upper and lower lobes; The right lung has a horizontal fissure besides an oblique fissure, so the right lung is divided into upper, middle and lower lobes. Furthermore, the left lung is long and narrow due to the left position of the heart, and the right lung is wide and short due to the upward bulge of the liver under the lung. As far as the left and right lung volumes are concerned, the right lung is larger than the left lung.

In addition, this interesting phenomenon of left-right asymmetry also exists in other organs of the human body. For example, the kidneys of urinary organs are left and right, but the left kidney is long and narrow, and the right kidney is short and wide; And because of the influence of the liver position, the position of the right kidney is slightly lower than that of the left kidney. The adrenal glands located above the left and right kidneys have different shapes. The right adrenal gland is triangular, and the left adrenal gland is approximately half-moon and slightly larger. The testis of male reproductive system is also a left and a right, located in the scrotum; But the position is different, generally the left side is slightly lower than the right side by three centimeters. I don't know if it is because of this reason that varicocele, one of the factors leading to male infertility, is mostly on the left side.

These are all organs with one on each side of the body. In the digestive system and cardiovascular system, some organs are unique in the body, but their anatomical positions are different in the left-right asymmetry. For example, most of the stomach is located on the left, and only 1/6 is located on the right; The pancreas is basically on the left side; The liver is the heaviest organ in the human body, accounting for about 2% of the body weight, but most of it is located on the right side. Therefore, if the human body is divided into two halves from the longitudinal axis, the right half will be heavier than the left half on the balance. Look at the intestines again. Except for the duodenum, the small intestine can probably be regarded as located in the middle and lateral. About 2/5 of the total length of jejunum is located in the upper left abdominal cavity, and about 3/5 of the total length of ileum is located in the upper right abdominal cavity. The situation of the large intestine is even more interesting, starting from the cecum of the right iliac fossa and rising along the right side of the abdominal posterior wall; Turn left below the right lobe of the liver to form a right curvature of the colon; Then left to the lower end of the spleen, and the folded face forms a left curvature of the colon; Then go down to the left iliac crest along the left side of the abdominal posterior wall and enter the pelvic cavity. Finally, it ends in the anus in the middle of the human body.

The most obvious example of the asymmetry of human organs in structure and function is probably the brain. People can often see the expression of "dominant hemisphere" in some popular science articles. The so-called "dominant hemisphere" is actually another name for the asymmetry of human language function in the left and right hemispheres of the brain. It means that human language function is mainly managed by the dominant hemisphere. Generally speaking, the dominant hemisphere of right-handed people is the left side. In principle, the dominant hemisphere of the left, that is, "left-handed", should be the right side. But in fact, half of the leftists' dominant hemisphere is on the left. So most people are in charge of logical thinking and abstract thinking, which is the function of language. In this way, the left hemisphere is often called the "language brain". The right hemisphere mainly accepts non-verbal materials and processes them, such as the perception of sound, rhythm and graphics and the thinking in images. The left hemisphere of the Japanese and some ethnic groups in the South Pacific not only controls the language, but also "listens to the sound". For example, people of some ethnic groups often turn a deaf ear to the sounds of insects, birds and running rivers, and even regard them as noise; However, the Japanese feel very different. They think that insects and birds are talking and talking, so the Japanese have a unique and extremely delicate understanding of nature. However, for piano, violin, symphony and other sounds, the Japanese, like people of other nationalities, can only enjoy them with their right brain.

According to the left-right asymmetry of brain function, some previously incomprehensible phenomena can also be explained. For example, why are dreams easy to forget? Some foreign scholars believe that dreams are mainly non-verbal experiences based on images, so they are mainly functional activities of non-dominant hemispheres. For most people, it is mainly the functional activity of the right hemisphere; Language is the functional activity of the dominant hemisphere, namely the left hemisphere. It is quite difficult to interpret and translate the dream images in the non-dominant hemisphere with the linguistic function of the dominant hemisphere, so most of the dream images that are difficult to describe and puzzling in language are forgotten by themselves.

The left and right hemispheres of the brain (also called left and right hemispheres) not only have a division of labor in language function, but also have a division of labor in controlling the feelings and movements of the left and right sides of the body. For example, the left hemisphere controls the feeling and movement of the right limb, and the right hemisphere controls the feeling and movement of the left limb. And this division of labor determines the division of labor of human limbs. The simplest example is eating. Most people hold chopsticks in their right hand and rice bowls in their left. If this division of labor between the right and left hands is reversed, I am afraid that few people are as flexible and handy.

Although the two halves of the human body are slightly heavier on the right, the center of gravity of the human body is located on the left. According to the research of modern sports physiology, whether right-handed or left-handed, when standing with feet together, the left foot touches the ground more than the right foot. This shows that people's left foot is the main axis of the center of gravity of the human body and plays a role in supporting the human body, so the left foot is also called "supporting foot". The function of the right foot is different from that of the left foot, mainly the same movement and speed adjustment, so the right foot is also called "sports foot". In the current track and field sports, running is carried out counterclockwise, that is, running along the inside of the left hand on the playground. But in the early Olympic Games, the running race was conducted clockwise. It was not until 1908 that the IOC officially adopted the anti-clockwise running rule that has been used to this day. This decision of the International Olympic Committee coincides with the view of modern sports physiology that "the left foot is the pillar of the body", because running along the inside of the left hand is easy to keep balance when turning. But people-including those who made the decision-didn't realize this at that time. According to this division of labor between left and right feet, we can explain why most athletes start with their left foot in squat: because the left foot supports the whole body weight, pushing back at the start can maximize the starting speed. In handball, football, judo, fencing and other antagonistic sports, people who support and control their balance with their left feet are overwhelming.

More interestingly, due to the different division of labor between hands and feet, many behaviors of people have certain directionality. According to the experimental investigation of Japan Railway Labor Science Research Institute, when dangerous objects suddenly appear in front, left front 20, right front 20 and directly above, the number of people hiding to the left is twice as much as that hiding to the right. Scholars explain that this is because the right foot is a sports foot, and its strength is greater than that of the left foot when dealing with sudden dangerous situations, so the direction of avoiding action is biased to the left. According to this experimental investigation, that is, according to the habitual direction of most people to avoid action, the traffic rule of "driving on the right while driving on the left" is obviously unreasonable; Because most people will instinctively avoid to the left when they suddenly encounter dangerous situations, they are likely to be knocked down by motor vehicles in the same direction.

Speaking of traffic accidents, according to the records of the Japanese police agency, motorcycle traffic casualties are also closely related to the asymmetric division of labor between people's left and right limbs. The casualties of motorcycle when turning right are much greater than when turning left. This can be considered to be related to the following situations: on the one hand, the center of gravity of the human body is located on the left. When turning right, the center of gravity obviously moves to the right, and the human body loses its balance because of its unstable center of gravity. On the other hand, for right-handers, no matter what they do, the right hand exerts more force than the left hand, and the action precedes the left hand. In addition, the center of gravity is on the left, so the upper body of right-handed people tends to lean to the left. However, when the motorcycle turns to the right, the left hand is required to work harder than the right hand, and the upper body is required to turn to the right to maintain the balance of movement. This is not easy for most right-handed people. From the point of view of mechanics and balance, it is required to increase the load on the outer foot of the arc when turning. For example, when turning right, the left foot is required to pedal harder, that is, the left foot is more powerful than the right foot to maintain the stability of the center of gravity and the balance of movements. But this is not easy for most right-handed people. Therefore, most people don't feel flexible when riding a motorcycle to turn right (the same is true for riding a bicycle). It can be seen that the statistics of the Japanese National Police Agency are not unreasonable and should attract the attention of motorcyclists.

When people think about the question "How many letters does the word Washington consist of", about 75% of people's eyes will be tilted to one side. Among them, the eyeball of the right hemisphere tends to be biased to the left; But if the left hemisphere is the dominant hemisphere, the eyeball tends to tilt to the right. This phenomenon has something to do with the suggestibility of hypnosis. Hypnosis is a hot topic in medical research in recent years, and it is a special sleep state guided by hypnotists by suggestive methods. Research shows that all hypnotized people have a common feature, that is, suggestibility increases, so the main means of hypnosis is suggestion. But who is more suggestive? Observations show that when thinking about the above question "How many letters does the word Washington consist of", people whose eyes are tilted to the left are more likely to be hinted, while those whose eyes are tilted to the right are less likely to be hinted. In other words, people whose right hemisphere is the dominant hemisphere are more likely to be hypnotized.

In addition, some unconscious actions and psychological activities of people are also related to the asymmetry between the left and right sides of the human body. For example, someone observed people walking up the stairs in the bookstore. If the stairs are divided into three roads: left, middle and right, then the people who go upstairs from the left stairs account for the majority, about 66%. If there are only two lanes on the left and right, then 87% people go upstairs from the left. When walking or driving, most people also tend to walk or drive on the left. This natural habit is considered to be closely related to rights and interests. Right-handed people's right hand is stronger than their left hand, so their range of activities is relatively larger, so naturally they subconsciously want to have more space than their left hand; When walking or driving on the left, there is more space on the right, so most people have this potential left-leaning habit. Some people even think that the position of the left and right seats may also have an impact on the atmosphere and results of the negotiations. If you are on the other person's left, you may feel the potential threat of the other person, because his heart is on the left, right next to your powerful right hand, and his left hand plays a less self-defense role.