Xu Yi was a little hesitant, these things are some knowledge of Western medicine, and it will undoubtedly be a huge project to explain this to a person in traditional Chinese medicine, so he raised his head and said with a smile: "This is a systematic scientific knowledge, but nothing that rises to the scientific level can be explained clearly by relying on one or two sentences." It contains a lot of theoretical knowledge in many disciplines, and it will definitely be very boring and difficult to understand, are you sure you can stand this thing so boring? Even if it is a simple explanation, it will have to be talked about for at least half an hour. ”

Liu Liping pursed her lips and said, "Isn't it more boring than the books in our class?" Then she looked at the time and said with a smile, "Anyway, you can't go to a nap for a while, and there's no harm in listening, you're going to make me dizzy, isn't it easier for me to go to a nap." ”

Xu Yi nodded and said: "It must be easier to understand than the things in the book, but you don't expect the things I talk about to be more rigorous and scientific, after all, I only have theoretical knowledge of these things, and they are not professional, and they will definitely not be able to explain if they are too specific." I've worked so hard, you have to say something, pour me a glass of water. ”

Liu Liping got up and poured a glass of water, held it and handed it to Xu Yi: "Teacher Xu, please drink water, and please give me more advice!"

"You're welcome. Xu Yi took the water cup with a smile, and then continued: "Man is not a plant, he has no cell wall. Maintaining cell morphology can only be achieved by water and other substances in the cell membrane, which is a bit like blowing up a balloon, the less gas is blown in, the balloon is smaller, and the more balloon there is, the balloon is bigger. More of them will explode, and the same will be true of cells. ”

"That's what you say. If you drink a glass of water, too much water will enter the cells. The cells are going to have to explode. ”

Xu Yi shook his head, "Naturally, it's not so simple and crude, cells have a certain mechanism to maintain their form and normal function. For example, the maintenance of morphology mainly relies on the osmotic pressure of crystals and colloids on both sides of the cell membrane to dynamically adjust the pressure difference between the inside and outside of the cell, so as to avoid being overblown or deflated. ”

"The cell membrane is essentially composed of phospholipids and proteins, phospholipids are the skeleton of the cell membrane, which is nothing to say, and there are a large number of protein groups on both sides of the cell membrane, as a macromolecular structure, protein molecules will naturally present different spatial structures. These structures determine the function of proteins. On the cell membrane, some proteins will connect the two sides of the cell membrane, forming some natural pores, which vary in size, which is the most basic channel for various substances to enter and exit the cell membrane. ”

"The existence of these protein channels makes the cell membrane a semi-permeable membrane, assuming that these channels are open, then molecules smaller than this channel can pass through these channels according to the difference in concentration between the two sides of the cell membrane, and molecules larger than this pore size cannot, you can understand this?" Xu Yi asked Liu Liping.

Liu Liping nodded. Then he asked, "How do things with larger pore sizes get in and out of the cells, are they all produced and sold by the cells themselves?"

Xu Yi shook his head with a smile and said, "If that's the case, then it's not a human body." It's a single-celled bacterium. ”

"What's more, even bacteria can't completely synthesize the required substances on their own, and the vast majority of substances can only be obtained from the outside world. For example, they can accept or send plasmids that express drug resistance. ”

"There are many kinds of cells in the whole human body, and there are different divisions of labor. From a microscopic point of view. The whole human body is more like a huge factory, and each cell is a small and delicate processing equipment. ”

"For example, the intestines and lungs are the places where the body mainly gets nutrients and oxygen from the outside world. These substances are continuously transported to various cells throughout the body through the humoral system, and then the substances they produce are transported to various tissues and organs throughout the body, and the products are utilized. ”

Liu Liping shook her head, expressing puzzlement. She is also more and more confused, after all, interlacing is like a mountain, these things in Western medicine are incompatible with her profession, listening to it makes her head big, no wonder Xu Yi wants to say that this thing is boring. "That's how different cells produce different substances, so how do these things get in and out of the cells. Didn't you just say that macromolecules can't pass through the cell membrane?"

"Yes, the most typical is like the hormones produced by the endocrine system, which are transported to various target cells through guò body fluids to produce different effects, most of these things are macromolecular substances, and it is impossible to directly penetrate the cell membrane with swagger, so many of them are combined with specific receptors on the cell membrane, and then activate specific enzymes in the cell to change the physiological state of the cell. ”

"So there are no hormones that can enter the cell through the cell membrane, and how do these things that can enter the cell get into the cell?"

"Most of the hormones that can act on cells are fat-soluble hormones, such as adrenocortical hormones, which can be dissolved in the cell membrane and then enter the cell, and a small number of hormones are bound to specific receptors on the cell surface through guò and then transported into the cell. Speaking of this, Xu Yi asked Liu Liping: "Have you ever played a game like Huarong Dao when you were a child?"

Seeing Liu Liping nodding, Xu Yi continued: "Playing Huarong Dao must be done by getting Cao Cao out, right, this requires repeatedly moving those chess pieces such as Guan Yu to make the space below suitable for Cao Cao." ”

"In a loose way, you can understand it this way: after the protein on the outside of the cell membrane is combined with the macromolecule in the extracellular fluid, it will naturally change its form, and even the macromolecular substance bound to it will also change its form, and the protein after changing the form will make enough gaps on the cell membrane for the macromolecular substance to pass through guò, just so that the macromolecule can be embedded in it, so that it can make it contact the protein molecule on the inside of the cell membrane. You can imagine that this foreign macromolecule is like a baton in a relay run, and the protein molecules transfer this macromolecular substance to each other and drag it to the inside of the cell. Even the largest substance, the cell can deform itself through guò, directly wrap the thing it wants to swallow with a large cell membrane, and then transport it to the cell. This is how white blood cells engulf bacteria, and after swallowing them, they kill and digest the bacteria, and if they can't kill them, then the cells will die together with the bacteria, which is the pus cells formed during infection. ”

"Oh, so I know, that is, cells can actually be selective about what can and can't get into the cell?"

Xu Yi nodded: "That's right, in fact, even a small molecule substance like water does not all penetrate into living cells through guò in a large way. If these channels are opened, it is like opening a faucet on the cell membrane, which can accelerate the entry and exit of water molecules in and out of the cell, and there are almost more than ten kinds of aquaporins found in human cells so far, which makes the exchange of water inside and outside the cell very fast. ”

"Even inorganic salts, in normal cells, most of them rely on special proteins on the surface of the cell membrane to form some special channels to enter and exit the cell, rather than simply entering the cell through guò osmosis, just like the concentration of potassium ions in normal cells is much higher than the concentration of extracellular fluid, so as to form a potential difference on both sides of the cell, accumulate potential energy, and provide energy for the cell to transport more substances. ”

"Of course, many times the proteins on the surface of the cell membrane transport substances in a way that requires them to maintain a specific morphology or bind to specific ions in order for these channels to open. ”

"The cells of the stratum corneum have died, and they must not be able to provide enough energy for the proteins on the surface, and the exposed environment will make the extracellular fluid between the cells easy to lose, thus affecting the properties of these proteins on the surface of the cell membrane, making them lose their activity, and naturally they will not be able to freely change the open and closed state of these channels, so the cell membrane of the dead cells has completely become relatively stable, covered with a semi-permeable membrane of fixed pore size. Anything larger than this pore size cannot enter the cell at all, nor can it come out of the cell, leaving only those smaller than these pore sizes to enter and exit the cell normally. ”

Liu Liping reacted at this time, "After the cell dies, the active protein components in the cell can only gradually decrease, and will not increase at all, do you want to say this?"

Xu Yi nodded: "Well, these protein macromolecular substances are the basis for the formation of colloidal osmotic pressure, the greater the number of proteins, the larger the volume of a single protein molecule, the easier it is to combine with water." Denaturation will lead to the reduction of the molecules or the solidification of the form, which naturally cannot effectively maintain the osmotic pressure of the colloid. ”

"Of course, colloidal osmotic pressure is only one aspect, in fact, the maintenance of cell morphology is mainly achieved by crystal osmotic pressure, and the same is true for dead cells. ”

In fact, the same is true of living cells, but in this process, cells can adjust the concentration of ions within a certain range according to the situation inside and outside the cell, so as to control the change of internal pressure. ”

"Because of the normal function of proteins on the cell membrane, normal cells will have a selective or active transport of these ions, transporting the desired ions to the inside of the cell, or transporting excessively high concentrations of ions to the outside of the cell. ”

Liu Liping asked, "Isn't there still crystals in these dead cells?"

Xu Yi nodded and said, "Theoretically yes, but there will be a problem here." ”

"What's the problem?" (to be continued......