The human digestive system , which includes the large intestine, is characterized by a variety of structure and functions of its various departments. This makes it difficult to diagnose digestive disorders, which affects the timeliness and effectiveness of therapeutic agents and methods. It is no secret that with the deterioration of the ecological environment, as well as with the irresponsible attitude of the person to his health, the number of gastroenterological diseases has increased in the world. They often turn into a chronic form, reducing the duration and quality of life of a person. This article is intended to explain in an accessible form the structure and functions of the human small and large intestine , as well as introduce the most common disorders in the work of these sections of the gastrointestinal tract.
General characteristics of the digestive system
Her work can be compared to a giant factory for the processing of food, its breakdown, assimilation and disposal of substances. In each section of the system, specific biochemical reactions occur with the participation of an arsenal of enzymes and biologically active substances, for example vitamins.
The large intestine, the structure and functions of which we are studying, is physiologically regarded as an organ involved in the secretion, digestion, absorption and removal of substances from the overlying departments. To understand the functions, we first consider how the large intestine works.
Colon membranes
On histological preparations, 4 layers are clearly visible: mucous, submucous, muscle and serous. They provide the main functions of the human colon: the formation of lymphocytes, which play a protective role, the synthesis of B vitamins and vitamin K with the participation of beneficial bacterial flora, the production of mucus, which improves the promotion of the chyme. One of the most important functions of the colon is the absorption of water and solutions of organic and inorganic substances, leading to the formation of feces from the chyme.
Colon morphology
It has a length of up to 1.5 m and is divided into 6 parts: the cecum with the appendix, the ascending, transverse, descending and sigmoid colon, as well as the rectum. The presence of three longitudinal muscle cords passing through the colon provides pendulum-like and peristaltic contractions of its walls. On palpation, the colon is easily diagnosed, since their mucous membrane has the appearance of alternating extensions and constrictions. They are formed in those places where the ring muscles of the intestine are most pronounced. For a more complete coverage of the functions of the human colon, we consider the features of its first section.
Cecum
Located in the right ileal part of the peritoneum, it has a length of 3 to 10 cm and looks like a bag. The appendix departs from the back. The walls of the cecum secrete enzymes, such as secretin, through which the chyme is digested. Also, excess water is absorbed.
The appendix contains micronodules that perform immune protective functions. Also, it is actively developing beneficial microflora. The most common pathologies of the cecum include typhlitis, appendicitis, tumors and polyps.
Ascending and transverse colon
They are a continuation of the cecum and do not secrete digestive enzymes, but only participate in the absorption of water and salt solutions. This leads to the densification of the chyme and the formation of feces from it. The large intestine, whose functions are primarily the evacuation of undigested food debris, has bends: the right (hepatic) and left (splenic), related to the transverse colon. Its functions are the production of mucus and the absorption of water and electrolytes. Diseases associated with the ascending colon include diverticulosis, polyposis, aganglion megacolon (Hirschsprung's disease), and colitis.
The transverse colon has the longest length. From above, it is in contact with the liver, gall bladder, spleen and the tail section of the pancreas. Its walls continue to secrete mucus and absorb water and mineral salts.
Digestion in the colon
It is carried out thanks to enzymes of intestinal juice: cathepsin, peptidase, lipase, amylase. Their activity is about 200 times lower than that of the corresponding enzymes of the small intestine. Extremely important is the fact. That for the processes of splitting in the large intestine, the presence of probiotics is necessary - groups of microorganisms that decompose fiber. These include bifidobacteria, lactobacilli.
In the large intestine, their total weight is 3-5 kg and is called intestinal microflora. It enhances the secretion of intestinal juice, affects protein-mineral metabolism, participates in the formation of immunity. The large intestine, the functions of which we named, is physiologically healthy if the processes of fermentation and decay are balanced in its metabolism. As soon as the composition of the microflora changes (for example, in case of malnutrition or as a result of drugs, especially antibiotics), putrefactive bacteria become activated and diseases arise: colitis, dysbiosis, dyspepsia.
Descending and sigmoid colon
In the area of the splenic bend there is a section about 30 cm long, in which the processes of absorption of water and electrolytes and the movement of feces continue. It is called the descending colon. At the location of the iliac crest is located its part having a sphincter of bally. Next, consider what the function of the colon in the last part of the colon called the sigmoid colon. It is partially mobile. If rumbling is heard during its palpation, it means that inflammation occurs in the sigmoid colon, accompanied by an accumulation of liquid contents and gases. In it, as in the transverse colon, a decrease in peristalsis often occurs, which leads to the phenomenon of constipation - a spastic delay in defecation. It is in these sections that the large intestine, whose functions are the transport and evacuation of toxins, forms feces, which then enter the rectum.
Violations of the sigmoid department have serious consequences for human health. With its inflammation (colitis or sigmoiditis), diarrhea and painful cramps in the left iliac part of the peritoneum are diagnosed. They are accompanied by bloating and belching. The physiologically normal decrease in pendulum and peristaltic movements in the sigmoid colon can be complicated by a sedentary lifestyle, an improper diet, depleted in fiber and plant fibers. The result of these disorders is constipation, leading to intoxication of the whole organism. In the sigmoid colon, the formation of herniform sacs is possible - protrusions leading to the development of diverticulosis. It is more common in old age, combined with irritable bowel syndrome. Its symptoms are alternating constipation and diarrhea, nausea, fever. The disease can be complicated by an abscess and is especially dangerous.
Rectum
It is the final section of the digestive canal. Its dyne is up to 15 cm. The large intestine, whose functions in this part of the gastrointestinal tract are to remove feces, ends with the anal canal and the anus. The rectum has sphincters: the first on the border with the sigmoid colon, the next three are called proximal, internal and arbitrary external. All of them participate in the physiologically normal process of defecation. The mucous layer of the rectum has folds with indentations called anal sinuses.
Between them and the anus is a ring-shaped area - hemorrhoidal zone. In it, thanks to the submucosal layer, a slight stretching and displacement of the mucous membrane, densely braided by capillaries of the rectal arteries and veins, is possible. The superior rectal vein has no valves, so its walls often expand - this leads to stagnation and the appearance of hemorrhoid cones. The lymphatic system of the rectum is involved in the immune system and prevents the spread of infection.
In this article, we studied the structure and basic functions of the colon.