Eating is essential for survival. Without food to provide nutrients, humans and many other heterotrophic organisms would not be able to survive.
Having food requires digestion, and our digestive system is responsible for breaking down food, breaking down individual nutrients for use by the body's cells.
So, when you put food in your mouth, do you know how your food works?
Let's take a look at the process of breaking down food into the smallest ingredients and understand how the digestive system works.
The saliva produced in the mouth, accompanied by the mechanical action of chewing, begins the process of digestion, because there are many enzymes with different effects in saliva.
There is a kind called salivary amylase (very familiar with it), which can break down the starch in food, and it is precisely because of the presence of saliva starch that when we eat steamed buns or rice, it will feel sweet; there is also some saliva lipase in saliva, which can break down fat.
After chewing food, this incompletely decomposed food enters the stomach through the esophagus.
Several enzymes secreted in the stomach can further break down the components of food.
When pepsinogen is converted to pepsin, it breaks down the protein into smaller peptides. The stomach also produces hormones like gastrin, which increases the mobility of the stomach.
You might think that the hydrochloric acid secreted by the stomach helps digestion (at least I think so), but in fact hydrochloric acid does not have any obvious digestive function.
Hydrochloric acid has two uses, first, to kill any pathogens that may enter with food; second, to inactivate salivary enzymes, which degenerate in the acidic environment of the stomach.
The main function of the stomach is to mix everything together.
If you eat a donut and then another burger, your stomach will churn everything together until there is no difference between the burger and the donut.
The muscles of the stomach are very strong and produce powerful contractions that stir food into chyme.
The digestive process of the stomach is divided into three stages: the first stage, the gastric stage and the intestinal stage.
The first phase begins with thinking about food, followed by the taste and sensation in the mouth when chewing.
These thoughts and the touch of food are eventually recorded in the bulbar. The bulbar stimulates gastric cells to secrete enzymes, hormones and other factors through the vagus nerve.
The stomach phase begins when food enters the stomach, causing the stomach to swell. Muscle contractions in mixed foods become stronger and gastric secretions increase.
The final stage is the intestinal stage.
When the stomach violently flips food, the pyloric sphincter (located at the junction of the small intestine and stomach) allows some food to pass through it into the small intestine.
When acidic chyme and the fat in chyme enter the duodenum, the duodenum begins to secrete hormones, the stomach gradually emptys, and food enters the small intestine.
When chymolide enters the small intestine, several things happen.
Simply put, the liver secretes bile salts through the gallbladder, while the pancreas secretes bicarbonate and various digestive enzymes to the duodenum. Bicarbonate ions neutralize acidic chyrus, making it alkaline. The role of bile salts is to emulsify fat, so that lipase can effectively break down fat.
Most digestive enzymes are secreted by the pancreas, such as trypsin, chymotrypsin, and carboxypeptidase (which breaks down peptides into amino acids), lipase (which breaks down fat into separate triglyceride molecules), and amylase and nuclease (which break down nucleic acids such as DNA and RNA).
The small intestine also has its own digestive enzymes. These are called brush-like margin enzymes and are located on small intestinal cells.
The small intestine is where the nutrients are absorbed the most. The duodenum, jejunum and ileum of the small intestine absorb different nutrients and have different functions.
Nutrient absorption occurs mainly in the duodenum and jejunum of the small intestine, and the absorption of certain nutrients by the ileum is also important.
When food enters the large intestine, most of the nutrients have already been absorbed.
The large intestine absorbs water and some of the remaining minerals, which convert chyme into feces by secreting mucus, while the gut microbiome (bacteria in the gut) alters chyme by chemical action.
After all this is over, the final product is our feces, waiting for us to excrete.
The digestive system doesn't work in the order of the foods you eat, that is, if you eat a donut and then eat another burger an hour later, your digestive system may digest the burger first.
The digestive process begins before certain nutrients are broken down, such as the carbohydrates we often eat, which begin to digest in the mouth and proteins in the stomach.
So, the next time you eat both a hamburger and a donut, remember that they all end up as a big ball of nutrients that are then excreted from your body in a brown or green poop.