The action of these organs is related to the food transformation process, which aims to help with the absorption of nutrients.
All this happens through mechanical and chemical processes.
Organs that make up the digestive system
The Digestive System (new nomenclature) is divided into two parts.
One of them is the digestive tract (properly speaking), previously known as the digestive tube. It is divided into three parts: upper, middle and lower. The other part corresponds to the accessory organs .
| Parts | Description |
|---|---|
| Upper digestive tract | Mouth, pharynx and esophagus. |
| Middle digestive tract | Stomach and small intestine (duodenum, jejunum and ileum). |
| Lower digestive tract | Large intestine (cecum, ascending, transverse, descending colon, the sigmoid colon and the rectum). |
| Attached bodies | Salivary glands, teeth, tongue, pancreas, liver and gallbladder. |
Upper digestive tract
The upper digestive tract is formed by the mouth, pharynx and esophagus.
Find out more details about each of these bodies below.
Mouth
The mouth is the gateway for food to enter the digestive tract. It is a cavity lined with mucous membranes, where food is moistened by saliva, produced by the salivary glands.
Chewing occurs in the mouth, which corresponds to the first stage of the mechanical digestion process. It occurs with the teeth and tongue.
In a second step, the enzymatic activity of ptyalin, which is salivary amylase, comes into play. It acts on the starch found in potatoes, wheat flour, and rice, transforming it into smaller maltose molecules.
Pharynx
The pharynx is a muscular membranous tube that communicates with the mouth, through the isthmus of the throat and at the other end with the esophagus.
To reach the esophagus, food, after being chewed, passes through the entire pharynx, which is a common channel for the digestive system and the respiratory system.
In the process of swallowing, the soft palate is retracted upwards and the tongue pushes the food into the pharynx, which contracts voluntarily and takes the food into the esophagus.
The penetration of food into the respiratory tract is prevented by the action of the epiglottis, which closes the communication hole with the larynx.
Esophagus
The esophagus is a muscular duct, controlled by the autonomic nervous system.
It is through waves of contractions, known as peristalsis or peristaltic movements, that the muscular duct squeezes the food and takes it towards the stomach.
Take the opportunity to deepen your knowledge about all the Systems of the Human Body .
Middle Digestive Tube
The middle digestive tract is formed by the stomach and small intestine (duodenum, jejunum and ileum).
Learn about each of them below.
Stomach
The stomach is a large pouch located in the abdomen and is responsible for digesting proteins.
The entrance to the organ is called the cardia, because it is very close to the heart, separated from it only by the diaphragm.
It has a small upper curvature and a large lower curvature. The most dilated part is called the “fundic region”, while the final part, a narrow region, is called the “pylorus”.
The simple act of chewing food already activates the production of hydrochloric acid in the stomach. However, it is only with the presence of food, of a protein nature, that the production of gastric juice begins. This juice is an aqueous solution, composed of water, salts, enzymes and hydrochloric acid.
The gastric mucosa is covered by a layer of mucus that protects it from aggression from gastric juice, since it is quite corrosive. Therefore, when there is an imbalance in this protection, the result is inflammation of the mucosa (gastritis) or the appearance of wounds (gastric ulcer).
Pepsin is the most potent enzyme in gastric juice and is regulated by the action of a hormone, gastrin.
Gastrin is produced in the stomach itself when protein molecules from food come into contact with the wall of the organ. Pepsin then breaks down the large protein molecules and transforms them into smaller molecules, which are proteoses and peptones.
Finally, gastric digestion lasts, on average, two to four hours. During this process, the stomach undergoes contractions that force the food against the pylorus, which opens and closes, allowing the chyme (white, foamy mass) to reach the small intestine in small portions.
Small intestine
The small intestine is lined with a wrinkled mucosa that has numerous projections. It is located between the stomach and the large intestine and has the function of secreting various digestive enzymes. This gives rise to small, soluble molecules: glucose, amino acids, glycerol, etc.
The small intestine is divided into three portions: the duodenum, the jejunum and the ileum.
The duodenum is the first portion of the small intestine to receive the chyme that comes from the stomach, which is still very acidic, being irritating to the duodenal mucosa.
Soon after, the chyme is bathed in bile. Bile is secreted by the liver and stored in the gallbladder, containing sodium bicarbonate and bile salts, which emulsify the lipids, fragmenting their droplets into thousands of micro droplets.
In addition, the chyme also receives pancreatic juice, produced in the pancreas. It contains enzymes, water and a large amount of sodium bicarbonate, as it helps to neutralize the chyme.
Thus, in a short period of time, the food “porridge” in the duodenum becomes alkaline and creates the necessary conditions for intra-intestinal digestion to occur.
The jejunum and ileum are considered the part of the small intestine where the transit of the food bolus is rapid, remaining empty most of the time during the digestive process.
Finally, along the small intestine, after all the nutrients have been absorbed, a thick paste is left, made up of unassimilated waste and bacteria. This paste, already fermented, goes to the large intestine.
Lower Digestive Tract
The lower digestive tract is formed by the large intestine, which has the following components: cecum, ascending, transverse and descending colon, the sigmoid curve and the rectum.
Large intestine
The large intestine is approximately 1.5 m long and 6 cm in diameter. It is the site of absorption of water (both ingested and digestive secretions), storage and elimination of digestive waste.
It is divided into three parts: the cecum, the colon (which is subdivided into ascending, transverse, descending and the sigmoid curve) and the rectum.
In the cecum, the first portion of the large intestine, food residues, already forming the “fecal bolus”, pass to the ascending colon, then to the transverse colon and then to the descending colon. In this portion, the fecal bolus remains stagnant for many hours, filling the portions of the sigmoid colon and the rectum.
The rectum is the final part of the large intestine, which ends with the anal canal and the anus, through which feces are eliminated.
To facilitate the passage of fecal matter, the glands in the mucosa of the large intestine secrete mucus to lubricate the fecal matter, facilitating its transit and elimination.
Note that plant fibers are not digested or absorbed by the digestive system, they pass through the entire digestive tract and form a significant percentage of fecal matter. Therefore, it is important to include fiber in your diet to help with the formation of feces.
