The main purpose of these bodies - the pre-processing of food before passing it to the gastrointestinal tract. Here, food is being shredded and moistened with saliva. At the stage of chewing food is cut into pieces and frays that, in general, not absolutely necessary, but greatly facilitates the further processes of digestion and absorption. To maximize the grinding of food needed a full set of teeth - no more of them can not compensate for the more intense or prolonged chewing.
Thanks salivation food acquires the consistency needed for swallowing. Chewing and dissolution of solid food components in saliva increase the sense of taste (taste, we feel due to the so-called taste buds on the tongue), which causes salivation reflexes and the development of gastric juice. Saliva is produced at a rate of about 1 liter a day! Saliva is also important to keep the teeth: in its failure, they are affected by caries and fall. Saliva also has a bactericidal action. Finally, under the action of saliva begins the digestion of carbohydrates.
Formed in the mouth the bolus is swallowed. This is due to the muscles of the mouth (voluntary contraction) and pharynx (involuntary). Moreover, during the initial phase of swallowing (tongue pushes the food when on) breathing is interrupted for a short time - it's a reflex. Then the food enters the esophagus - muscular tube length of 25-35 cm This tube has two muscular "ring" - the sphincter, one at the entrance (prevents the free passage of air into the esophagus, in which the pressure slightly below atmospheric pressure), the other at the exit (prevents casting of stomach contents back up into the esophagus). Malfunction of the esophagus and its sphincter can cause symptoms.
The stomach has several functions: it collects swallowed food, stomach acid is produced under the action of which food undergoes chemical changes also occur in the stomach and the mechanical grinding of food. As a result, food is converted into so-called chyme that enters the duodenum and then into the intestine for further digestion and absorption.
The muscular activity of the stomach provides: food storage, mixing and grinding of food (due to the fact that under the influence of muscle contractions solid particles move and rub against each other), the further promotion of food in the intestines. Gastric emptying, that is, the further promotion of food in the intestines, as regulated by the autonomic nervous system and hormones, as well as the "gut brain." The rate of gastric emptying also depends on the composition of food: for example, acidic contents from the stomach is evacuated more slowly than neutral, and fatty foods - more slowly than protein.
Special cells in the stomach at night produce 2-3 liters of gastric juice! This stimulates the production of mechanical stretching of the stomach wall with food and chemical effects of certain food components (mainly products of protein digestion). In addition, in the stomach hormone gastrin and hydrochloric acid, promotes the destruction of proteins (for further digestion) and a bactericidal action. Also in the stomach produces mucus and bicarbonate (alkaline secret) to protect the gastric mucosa.
Finally, in the gastric juice is present intrinsic factor required for absorption of vitamin B12 (in certain diseases of the stomach does not produce intrinsic factor, causing a specific type of anemia - the so-called pernicious anemia). Most often, dysfunction of the stomach involve a violation of secretion - in excess of the hydrochloric acid because of the "samoperevarivaniya" may develop a peptic ulcer and / or duodenal ulcers, and insufficient production of hydrochloric acid is in atrophic gastritis.
The small intestine
The small intestine serves several important functions: mixing the chyme with the secrets of the pancreas, liver (bile) and intestinal mucosa, digestion, absorption of digested; promotion of the remaining substances below the gastrointestinal tract, hormones and immune defense.
The small intestine consists of the following sections: duodenum, jejunum and ileum. Of great importance for the absorption process specially arranged cells of the intestinal mucosa - enterocytes. Water and dissolved substances are transported either through enterocytes themselves (through special channels in the cells of the active route), or through the space between them (extracellular) - passively, by diffusion.
In an average day in the small intestine is about 9 liters of fluid! This is a 2 liter of fluid entering the intestine from the blood, and 7 liters - with a secret and very different glands of the intestinal mucosa. However, only 1% (or about 100 ml) was excreted in the feces. The remaining liquid is drawn back. In addition, in the small intestine are absorbed and digested by the digestive juices and enzymes specific carbohydrates, proteins (and their components - peptides and amino acids) and lipids, and minerals.
When malabsorption (sprue) in the small intestine is no absorption of substances in its entirety. Malabsorption may occur in various diseases, but is sometimes caused by artificially (with surgery) for treatment of severe obesity (see page dedicated to surgical treatment of obesity).
The large intestine
In the large intestine (includes the cecum, ascending, transverse and descending parts of the colon, sigmoid colon and rectum) is the mixing of chyme under the action of peristalsis (smooth muscle contraction), the concentration of the chyme through the reabsorption of water and its further splitting with living in the colon bacteria. Undigested food remains on track in the form of the stool to the rectum.
Different departments of the large intestine perform different functions. In the caecum there is a splitting of chyme with bacteria and the absorption of water (there is still chyme liquid consistency). These processes are going on in all parts of the colon, which leads to compaction of the intestinal contents. A sigmoid and rectum are mainly tanks. In the large intestine also has its own protective (immune) tissue.
Dysmotility colon leads to constipation or diarrhea. A shortage of "good" bacteria, or excessive amounts of "bad" (and too active for reproduction "harmful" and can be "helpful" bacteria) - the so-called dysbiosis - leads to various pathological manifestations and may contribute to the development of a number of diseases.
The main role in the digestion of intensive substances coming from food, when it moves from the stomach into the small intestine plays pancreatic juice containing bicarbonate (neutralizes the acidic chyme) and digestive enzymes (hydrolase) that cleave the main substance in the food. The pancreas is able to devote a day of 1.5 liters of secretion.
Pancreatic duct through which the secret is released, called the duodenum. Here we do not consider another important function of the pancreas - the regulation of carbohydrate metabolism (eg, insulin), because this process involves another area of physiology.
If you violate the digestive function of the pancreas (that is, for example, chronic pancreatitis), there is lack of certain enzymes, which is manifested by certain symptoms. In rare cases it may be samoperevarivanie own enzymes of the pancreas (acute pancreatitis), whose consequences are serious and require immediate medical.
Liver and biliary system
The liver occupies a central place in metabolism: protein, fat and carbohydrates, as well as hormones and vitamins. The liver synthesizes many vital body substances. In addition, through the liver detoxified many harmful and toxic substances. From the standpoint of the physiology of digestion, we consider the excretory function of the liver: that is, the secretion of bile.
Bile is a complex structure and many functions. Thus the bile are the final products of metabolism, such as bilirubin (a breakdown product of hemoglobin), as well as drugs and toxins. Isolation of the bile cholesterol plays an important role in the regulation of its balance sheet. Bile acids in bile, essential for digestion of fats. The composition of bile coming out of the bile ducts of the liver and gall bladder contained unequal.
In gall bladder bile is more concentrated (due to reabsorption of water from the hepatic bile). Bile acids are highlighted in the duodenum, and their converse is actively absorbed in the final section of the ileum. The total amount of bile acids in the body is not enough to break down all the fat from food. However, the body does not experience a shortage of bile acids, as they repeatedly circulate through the intestines and liver.
The best-known and widespread disruption of normal function of the biliary system - this is the precipitation of cholesterol with the formation of cholesterol gallstones (cholelithiasis). Overweight - a risk factor increasing the relative content of cholesterol in the body and, therefore, gallstone disease. So, we have considered only a very small part of the physiology of the gastrointestinal tract. This is a complicated and incredibly finely arranged system! And so before you get involved in her work, please, consult with your doctor, who knows the intricacies and help you not only hurt yourself, but also improve your health and lead you to Health!