The intestine is essentially a long tube, starting from our mouth and ending in our anus. We usually think that the intestine helps us digest food and absorb nutrients. In fact, its importance goes far beyond this. Let's learn some basic "intestinal" knowledge.
What is the job of the intestine?
In fact, as we know, the intestine breaks down food into nutrients that can be absorbed and utilized by the body. After processing all the useful things provided by food, the intestines will discharge waste.
At the same time, the intestine also helps to regulate the immune system. 70% of our immune cells are in our intestines. Some foreign invaders may enter our bodies through the food we eat, and immune cells and beneficial bacteria in the digestive system provide the first line of defense for the invaders.
Digestion is the primary task of the intestine. Digestion is the process by which the body converts food into energy that cells can use. The cells that make up our body can't get the nutrients they need directly from food. Digestion is basically to break down macromolecules in food into small molecules, which can be absorbed by cells and used for our body functions.
Cells are the cornerstone of life. In our body, cells with similar structures form tissues, which in turn form organs, and an organ formation system, which together play certain specific functions. Speaking of the intestine, it is an important part of our digestive system, which is responsible for transforming food into small energy packages that the body can use. We need this process to survive.
Digestion involves the coordination of muscles and enzymes, as well as the coordination of multiple organs and systems. This process is both mechanical and chemical, just like there are "engines" and "biochemical laboratories" in our bodies.
The mechanical part of digestion is related to physical forces, which are at work in the process of digestion: food is chewed and then swallowed; In our stomachs, food is constantly being stirred; Gastrointestinal peristalsis is a process of internal muscle contraction, which makes food move forward in digestive tract. These are all very mechanical processes.
The chemical part of digestion involves the action of digestive juice and digestive enzymes, which break down food particles into nutrients and then be absorbed by the body. The chemical action of digestion is simultaneous with all mechanical actions. Different parts of the digestive tract will release different digestive juices and digestive enzymes to help transform food particles into small molecules of nutrients.
Another job of the intestine is to get nutrients from food, absorb nutrients, and then transport them to other systems of the body. Nutrients refer to nutrients that are necessary to maintain life and are necessary to maintain the normal work of the body.
So how does our body absorb and use nutrition? That depends on what nutrition it is. Nutrients are mainly divided into two categories: macronutrients and micronutrients.
Macronutrients include carbohydrates, protein and fats, which can be decomposed relatively quickly to provide more direct energy for the body.
Micronutrients include vitamins and minerals. These substances act as catalysts in chemical reactions, which include the release of energy from macronutrients. Like many substances in the human body, these two nutrients need to have a biological relationship, in other words, to work together happily.
Almost all nutrient absorption is carried out in the small intestine. The integrity of the inner wall of small intestine is one of the most important factors for intestinal health. Nutrients enter our circulatory system through the small intestinal wall, where they are transported to other parts of the body through blood circulation or lymphatic circulation. In other words, sometimes nutrients will enter our blood directly, while at other times, nutrients will be released by other ways of carrying body fluids and cells, which will help the body's natural immunity and resist diseases.
The two main ways of nutrients passing through the intestinal wall are called active transportation and passive transportation. In passive transportation, nutrients can be transferred from the intestine to the blood, which requires little cellular energy. This is a very easy path, and all vitamins enter our blood through passive transportation. In the process of active transportation, nutrients need a molecule called "carrier", which is usually an enzyme to help nutrients directly enter the whole circulation of the body. Both ways help to transfer nutrients to other systems of the body.
We all produce waste in the process of digestion, so how are these wastes removed? Understanding the mechanism of human waste removal can help us understand what is normal, so that we can better find problems and deal with them in time.
When our digestive system and circulatory system break down food and absorb nutrients together, there will be some substances left. These undigested and unused food residues will enter our large intestine, and the water in it will be absorbed. They will eventually turn into feces, and then pass through the rectum and anus, so that we can get rid of these wastes.
So where does urine come from? This is the responsibility of the urinary system. Our kidneys are like a filter. When blood flows through the kidney, urea, inorganic salts, glucose, water and some harmful substances in the blood will enter the renal capsule through glomerular filtration, forming protourine. When they flow through the renal tubules, some useful substances will be reabsorbed by the renal tubules and return to the blood, such as all glucose, some inorganic salts and water, and the rest will form urine which will be transported to the bladder for storage through the ureter and finally discharged through the urethra.
About 70% of human immune cells are located in the digestive system, and most of them are connected with intestinal mucosa. Our first contact with diseases is usually the intestine. When harmful bacteria and viruses enter our bodies through the intestines, a healthy immune system will be able to attack them and expel them to avoid getting sick.
In addition to immune cells, our intestines are also home to trillions of beneficial bacteria, which play a key role in the healthy operation of our immune system. Ideally, these bacteria form a biological relationship with our immune cells and intestinal wall to keep everything in the intestine running normally and keep harmful invaders such as pathogens out.
Our diet directly affects the number and composition of bacteria in our intestines. Unhealthy food will promote the excessive growth of harmful bacteria, thus crowding out healthy and beneficial bacteria. This imbalance will damage the function of intestinal immune system.
Over time, the imbalance of intestinal flora will also damage the integrity of intestinal wall and the ability of intestinal wall to prevent harmful bacteria, undigested food particles and pathogens from entering the circulatory system. This situation is what we usually call intestinal leakage. Intestinal leakage can also lead to immune dysfunction, which leads to food intolerance, allergies, autoimmune disorders and inflammation. Therefore, it is extremely important to take good care of our intestines through a correct diet.
How do the various parts of the intestine work together?
Intestines are very important to our health. It works with other organs of our nervous system, circulatory system and digestive system. When we are hungry, our central nervous system will begin to send signals to our gastrointestinal tract and secrete some enzymes and hormones that help us break down food. Once the food enters, different parts of the digestive system will start to work together.
When we start chewing and swallowing food, intestinal secretions will increase and muscles will begin to contract. After the stomach is agitated, food moves forward through the small intestine and large intestine. Finally, when the nutrients in the food are completely absorbed, the remaining residues will be discharged through the anus.
So, how does every part of our intestines complete this process?
Our central nervous system will send a signal to the salivary glands in our mouth, making them produce and secrete more saliva. So, food really makes your mouth water. Once the food reaches our tongue, our taste buds start to act, and the salivary glands will produce more saliva. Saliva contains an important digestive enzyme called amylase, which can break down the starch we eat and turn it into simple sugar. The main work of decomposing starch is done in the small intestine, but it begins in our mouth. About 30% of starch is digested in the mouth.
With the help of the tongue, our teeth push food and grind it. This mechanical process will break down food into small pieces and lead to more saliva secretion. After chewing, the soft food in the mouth is now ready to enter the next stop in the intestine.
The pharynx is what we usually call the throat. It receives the food we have chewed, and our tongues and jaws push it there. Our pharynx divides into trachea and esophagus, the trachea leads to the lungs and the esophagus leads to the stomach. So sometimes, food does not directly enter our stomach, and they may accidentally enter the trachea, causing cough; In severe cases, food stuck in the trachea will affect our breathing and lead to suffocation. So, take your time when you eat, chew slowly.
Ideally, when swallowing, the trachea will be temporarily closed so that food can enter the esophagus. Our esophagus is made up of muscles, which contract and push food to the stomach.
There is a sphincter right in front of the stomach entrance. This is an annular muscle called the lower esophageal sphincter. This muscle is the gatekeeper of the stomach. Open it to let food in, but it must be closed to keep food, digestive enzymes and stomach acid in the stomach to prevent reflux.
Our stomach is a cystic organ, and its inner layer is full of muscles, which can grind food into liquid or paste. Our gastric mucosa is also home to receptor cells, which send extra signals to more glands and release more gastric juice. Muscle contraction of the stomach wall and gastric juice helps to further decompose food, and then pushes it into the small intestine through another muscle called pyloric sphincter at the outlet of the stomach.
The small intestine can be said to be the MVP of the whole digestive tract, and most digestion and almost all nutrient absorption are carried out in the small intestine.
Like other parts of the digestive tract, the small intestine also relies on the secretion of digestive enzymes and other substances to further decompose food particles. The other two digestive organs that do not belong to the gastrointestinal tract-pancreas and gallbladder-secrete their secretions into the small intestine through special conduits or passages from these organs to the small intestine. Intestinal epithelial cells on the surface of small intestine also secrete their own digestive enzymes.
There are some unique structures on the inner wall of the small intestine, called small intestinal villi. These finger hairs are covered with smaller microvilli. The purpose of these structures is to increase the surface area of the intestine to increase the absorption of nutrients. Villi and microvilli capture nutrients in the intestine like small antennae.
Intestinal epithelial cells release nutrients into the circulatory system through the passive and active transport mechanisms we discussed earlier, and then transport nutrients to other parts of the body. All the functions of the small intestine are also affected by the health status of the bacteria living there.
The large intestine is much shorter than the small intestine, but its interior is much more spacious, and there are no villi and microvilli here. We usually think that the main job of the large intestine is to absorb potassium and sodium and the remaining water in food residue. In fact, there are more bacteria in the large intestine, which is also the main place for the decomposition and utilization of dietary fiber in food. The human body itself cannot produce enzymes that break down dietary fiber, so dietary fiber in food is usually not digested in the small intestine. They enter the large intestine completely and are metabolized by bacteria in the large intestine to produce short-chain fatty acids necessary for human health. Eventually, the remaining food residues form feces.
The feces are eventually pushed into the rectum, causing the rectal wall to stretch. The receptors on the rectal wall communicate with our spinal cord and increase the pressure of the internal anal sphincter. This is when we want to go to the toilet. Of course, at this time, if the external conditions do not allow defecation, we can control defecation by contracting the external anal sphincter.
How does the intestine work with the brain?
Our brain is responsible for storing memories and letting us experience various emotions. It also sends signals to other systems of the body, including our digestive system, to prepare for the normal operation of these systems. Receptors and nerves in the intestine and brain enable them to communicate with each other. The neural pathway connecting the intestine and the brain not only involves and is influenced by digestion, but also participates in and is influenced by emotions.
Our brain is responsible for processing five basic human senses, including sight, hearing, taste, smell and touch. The combination of taste and smell allows us to experience the real taste of food. Hunger and thirst are physiological factors that make people eat. We can feel these factors in different parts of the intestine, but what to eat and how to eat will be influenced by other more subtle psychological factors.
Sometimes, we may eat when we are not hungry or out of boredom or sadness; Sometimes, certain smells activate pleasure in the brain, and you may eat more for pleasure rather than demand. Then, when you want to repeat this experience, you will choose those foods that satisfy this taste preference. Taste is an irresistible force. Our impulse to pursue happiness is not always consistent with reasonable nutritional choices, which is also the fundamental contradiction of many intestinal health problems. What we long for is not always the best for us.
Many nerves extend from the brain to other parts of the body, of which the vagus nerve is the longest and extends to many organs in the chest and abdomen. It is also a highway for communication between our intestines and our brains.
Before we put food in our mouth, our brain releases a special chemical messenger called a neurotransmitter through the vagus nerve. These chemical messengers send signals to our digestive tract along this path, making it secrete saliva and gastric juice to prepare for receiving food. Vagus nerve also helps swallowing and intestinal wall muscle contraction, pushing food forward. Similarly, this neural pathway also lets our brains know that we are full, so we will stop eating.
Vagus nerve can also affect our heart rate, blood pressure and breathing. Just as pleasure receptors in the brain affect our dietary choices, vagus nerve also affects our response to stress. When we are faced with an emotional situation or a stressful situation, the vagus nerve will be overstimulated. This is why when we are nervous or afraid, we often feel stomachache. Vagus nerve can help activate the fight-or-flight response, reduce the production of digestive juice, and limit the blood flow to our intestines. This is why when we are too nervous, we may lose our appetite.
Vagus nerve transmits signals back and forth between our intestines and our brain. When the vagus nerve is extremely active, our blood pressure and heart rate will suddenly drop, temporarily cutting off the blood supply to the brain. If this happens, we will feel dizzy, nauseous and irritable, and may even faint.
When we are still in our mother's womb, some nerve tissues that form our central nervous system will also form our intestinal nervous system. The intestinal nervous system consists of about 65438+ billion nerve cells, which not only helps to control digestion, but also participates in many other important functions. Vagus nerve helps two nervous systems communicate with each other, and they use the same type of neurotransmitter to achieve this. The intestinal nervous system is located in the inner wall of the intestine and sends signals back and forth to the brain during digestion. However, the intestinal nervous system does much more than that.
The intestine is also called the second brain. The nervous system of the intestine can't think for us, but its series of neural pathways can play a role in dealing with most digestion independently of the brain. It is so complicated that it is not only responsible for digestion, but also plays an important role in regulating our overall mood and physical health.
90% nerve fibers in our vagus nerve are responsible for transmitting signals from the intestine to the brain, and this one-way signal transmission will definitely have an impact. Our intestinal health and the signals sent by the intestinal nervous system to the brain will affect our brain function and behavior, and play a role in many neuropsychiatric diseases. 5- hydroxytryptamine is an important neurotransmitter in human body, which affects our mood, appetite, cardiovascular function and muscle function. 95% of serotonin in our body is synthesized in the intestine. Most of our brain cells are affected by serotonin, and vagus nerve uses serotonin as one of its neurotransmitters, sending signals to our brain almost continuously.
Now more and more cutting-edge research is gradually uncovering the mystery of how the intestine affects the immune system, mental state and overall health. This is very important, because intestinal health can be largely controlled by ourselves. Understanding the internal working mechanism of intestine is helpful to prevent, alleviate and even reverse many diseases. By choosing a healthy diet and lifestyle to optimize our intestinal health, we can control our overall health more easily.
The pictures are all from the Internet.