One of the most significant components of human life is digestion, because namely during this process, the necessary proteins, fats, carbohydrates, vitamins, minerals, and other useful ingredients enter the body. That is why the proper functioning of the human digestive system serves as the basis for full-fledged life support during the main processes in the digestive tract. Moreover, the digestive system is also responsible for the water-electrolytic balance, regulating the rate of fluid intake from food. The functions of the gastrointestinal tract can be summarized as follows (Hoffman 9-14):
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- Motor function. Due to the middle (muscle) membrane of the digestive tract, muscle contraction-relaxation, food taking is carried out, following chewing, swallowing, mixing, and moving food along the digestive canal.
- Secretory function is carried out due to the digestive juices, that are produced by the glandular cells located in the mucous membrane (inner) of the canal. These secrets contain enzymes (reaction accelerators) that carry out the chemical processing of food (hydrolysis of food substances).
- Excretory function provides the secretion of metabolic products by the digestive glands in the gastrointestinal tract.
- Absorption function ‑ the process of assimilation of nutrients through the wall of the gastrointestinal tract into the blood and lymph.
The gastrointestinal tract is a convoluted tube that begins with the mouth and ends with the anus. The digestive system includes the following: the oral cavity with organs located in it and the adjacent large salivary glands; pharynx; esophagus; stomach; small and large intestine; liver; pancreas (Rogers 15).
The oral cavity, pharynx, and esophagus located in the area of the human head, neck, and chest cavity have a relatively straight direction. In the oral cavity, food enters the throat, where there is a cross of digestive and respiratory tracts. Then the esophagus comes, through which food mixed with saliva enters the stomach. In the oral cavity, the primary processing of food occurs, which consists of its mechanical grinding with the help of the tongue and teeth and turning into a food lump.
The salivary glands secrete saliva, the enzymes of which start the breakdown of carbohydrates in food (Smith and Morton 29). Then, through the throat and esophagus, food enters the stomach, where it is digested under the influence of gastric juice.
The stomach is a thick-walled muscle sac located under the diaphragm in the left half of the abdominal cavity. By reducing the walls of the stomach, its contents are mixed. Many glands concentrated in the mucous wall of the stomach secrete gastric juice containing enzymes and hydrochloric acid. After this, partially digested food enters the anterior part of the small intestine ‑ the duodenum.
The small intestine consists of the duodenum, jejunum, and ileum. In the duodenum, food is exposed to the action of pancreatic juice, bile, and also the juice of the glands located in its wall. In the jejunum and ileum, the final digestion of food and absorption of nutrients into the blood occurs. Undigested residues enter the colon. Here they are accumulated and are subject to removal from the body in the form of feces. The initial part of the colon is called the blind, and the appendix is following it.
Digestive glands include salivary glands, microscopic glands of the stomach and intestines, pancreas, and liver. The liver is the largest gland in the human body. It is located on the right under the diaphragm (Rogers 42). Bile is produced in the liver, which flows through the ducts into the gall bladder, where it accumulates and enters the intestine as needed. The liver retains toxic substances and protects the body from poisoning. The pancreas also belongs to the digestive glands that secrete juices and turn complex nutrients into simpler and more soluble in water. It is located between the stomach and the duodenum. Pancreatic juice contains enzymes that break down proteins, fats, and carbohydrates; 1–1.5 liters of pancreatic juice is secreted per day (Hoffman 30).
The correct sequential operation of the elements of the digestive system in time and space is ensured by regular processes of various levels. Enzymatic activity is characteristic of each section of the digestive tract and is maximum at a certain pH value of the medium. For example, in the stomach, the digestive process is carried out in an acidic environment.
Acidic content passing into the duodenum is neutralized, and intestinal digestion occurs in a neutral and slightly alkaline environment created by secrets secreted into the intestine ‑ bile, pancreatic juices, and intestinal secretions, which inactivate gastric enzymes (Smith and Morton 24). Intestinal digestion occurs in a neutral and slightly alkaline environment, first in the type of abdominal and then parietal digestion, ending with the absorption of hydrolysis products ‑ nutrients.
The degradation of nutrients by the type of cavity and parietal digestion is carried out by hydrolytic enzymes, each of which has specificity expressed to one degree or another. A set of enzymes in the secretions of the digestive glands has specific and individual characteristics, adapted to the digestion of the food that is characteristic of this region, and those nutrients that prevail in the diet.
Each digestion department has its internal environment, which serves as the basis for the functions assigned to it. The organs of the gastrointestinal tract, together with the auxiliary glands, gradually break down each component of the food, separating what the body needs and sending the rest of the absorbed food to waste. If at any of these stages a malfunction occurs, the organs and systems do not receive enough energy resources and, therefore, cannot fully perform their functions, causing an imbalance of the whole organism. Violations of the normal functioning of the digestive system can lead to the development of several diseases.
Hoffman, Gretchen. Digestive System. Benchmark Books, 2008.
Rogers, Kara. The Digestive System. Rosen Education Service, 2010.
Smith, Margaret E., and Dion G. Morton. The Digestive System: Systems of the Body Series. Churchill Livingstone, 2011.