Although medical knowledge of human body is extremely limited at present, the existing knowledge is enough to make us marvel at the exquisiteness of human body structure and function. Every system and organ of the human body is a masterpiece of the creator, even those seemingly insignificant things have profound intentions. For example, there are many kinds of human hair, each of which has different shapes and functions, so it will not be confused. Hair protects the head and has beautiful functions, so it can grow very long. The Bible says that long hair is a woman's glory, so women seldom go bald. Eyebrows are located above the eyes and divided to the sides to prevent sweat and rain from flowing into the eyes. Eyelashes are born at the edges of the upper and lower eyelids to prevent foreign bodies from entering the eyes and bend forward in a special arc, which does not hinder the line of sight. When you close your eyes, they can cross up and down without stabbing your eyes. Eyebrows and eyelashes that grow too long will hinder vision, so they will never grow as long as hair and beard. Nose hair is to filter the breathing air, so it is born on the inside of the nostril and obliquely to the outside. If it is inward, foreign objects will easily enter but difficult to get out. Axillary hair is to overcome local friction and help sweat evaporate. If there is no armpit hair, people have to hold their arms high all day, otherwise the local skin will become inflamed due to friction and humidity. According to its functional requirements, armpit hair can neither grow as long as hair nor as short as eyebrows, and it is soft and curly. If you are hard and upright, don't stab your flesh? People's intestinal epithelium also has cilia, all of which grow downward and can vibrate together, and their vibration waves are also from top to bottom, thus pushing down the intestinal contents. The epithelium of trachea and bronchus also has cilia, but the direction of its growth and vibration is opposite to that of intestine, which is retrograde. Because only in this way can the sputum be pushed up to the throat and spit out. If the trachea and bronchus are blocked by phlegm according to the general law, people will not live.