In humans, the digestive system, also called the digestive system, is made up of the mouth, esophagus, stomach, intestine, and anus. Some glands, such as the pancreas, liver, and salivary glands, also help digest food.
In the mouth we find the tongue and teeth, which help prepare food for digestion, making mechanical digestion. We can say that digestion begins in the mouth, because the teeth are responsible for cutting and crushing the food, so that, in smaller pieces, they suffer better the action of digestive enzymes, making digestion faster. The tongue also participates in digestion, in which we find the taste buttons capable of detecting the taste. In addition to identifying the flavors, it also has the function of manipulating the food and mixing it with the saliva produced by the salivary glands. Saliva, in addition to uniting the mucosa and protecting the mouth from bacteria, lubricates food for easier chewing, taste and swallowing. By containing salivary amylase, also called ptialine, saliva acts in the digestion of starch and glycogen, breaking it into maltose. Salivar amylase acts at a neutral pH in the mouth and is deactivated when it reaches the stomach with acid pH.
When the food is chewed and mixed with saliva it is called meatloaf.
With the help of the tongue, that cake is pushed into the esophagus by the process we call swallowing. Pharynx and larynx communicate through a channel that carries air to the lungs. When the Food Pie passes through that place, a membrane that closes the larynx comes into action, thus preventing any food from falling into the airways. That membrane that closes the larynx is called epiglottis. Sometimes the epiglottis may fail in the passage of any food, dropping small amounts of food into the larynx, which causes choking and coughing.
After swallowing, the food is inserted into the stomach through the esophagus, through muscle movements called peristaltic movements or peristaltism.
When in the stomach, the food cake suffers from gastric juice, a solution rich in hydrochloric acid and digestive enzymes. Gastric juice is produced by the stomach glands that are located in the invagination of the mucosa of the stomach wall. Hydrochloric acid has an extremely acid pH, acts in the denaturing of proteins (facilitating their digestion), facilitates the absorption of calcium and iron by the body and destroys thousands of bacteria.
Pepsin is the main enzyme found in gastric juice. This enzyme is secreted by pepsinogen-like cells. When it suffers from the action of hydrochloric acid, it becomes pepsin and begins to act, digesting proteins and breaking peptide bonds between some amino acids.
But it is not only the pepsin that is present in the gastric juice. Lipase, an enzyme that breaks lipids, and renin, which acts in the coagulation of casein (milk protein), are also present in hydrochloric acid. Renin is produced in large quantities in the stomach of babies and children and is little produced by the stomach of adults. Some of the water and salts, some medications, and alcohol are also absorbed into the stomach.
After remaining in the stomach for 2 to 4 hours, the food becomes a semi-liquid and acidified mass, called chemo.
After leaving the stomach, the chemo is taken to the small intestine, which consists of three parts: the duodenum, jejunum, and ileus. In the duodenum, there are thousands of glands that produce intestinal juice, also called enteric juice, which contains enzymes. Also in the duodenum are released the secretions produced by the pancreas (pancreatic juice) and secretions produced by the liver (bile).
The pancreatic juice contains several enzymes, such as trypsin and quimiotripsina, which break the proteins into smaller molecules; pancreatic lipase, which breaks fats into acid graxo and glycerol; and pancreatic amylase, which breaks starch and glycogen and converts them into maltose. Also in pancreatic juice there are enzymes that break DNA and RNA, called deoxyribonucleases and ribonucleases, respectively. Bile contains bile salts that transform fats into droplets that mix with water, facilitating the action of pancreatic lipase.
After going through all these transformations in the small intestine, digestion is carried out in the jejunum and ileus region, which synthesizes an intestinal juice composed of maltose enzymes (transformation of maltose into glucose) and sacarase (transformation of fructose into glucose), lactase (transformation of lactose into glucose and galactose), aminopeptidases, dipeptidases and tripeptidases.
After going through all that process, the chemo becomes a whitish liquid and is called a Kilo. It is in the small intestine that most nutrients are absorbed, which passes into the blood and lymph vessels.