Motor function of gastrointestinal tract

Phases of swallowing act of digestive lump There are 3 phases of swallowing: oral, pharyngeal, esophageal. Oral phase – food passes from the mouth into the pharynx through oropharyngeal isthmus. It is voluntary as well as reflex. This is initiated when the bolus reaches a depression in the middle of the tongue. The stimulation of the receptors already described starts the swallowing reflex. Mastication and respiration are stop. The pharyngeal phase – food is pushed from the pharynx into the esophagus. Stage 1 and 2 are completed normally in 1 second. The esophageal stage – food reaching the upper end of the esophagus is passed into the stomach. It takes about 10 seconds. The 2 and 3 stages are pure reflex actions. Swallowing can be done as voluntary act, but mostly it is a reflex action.

Regulation of swallowing act From the receptors of mucous membrane covering oral cavity afferent impulses arise and travel via the fifth, ninth and tenth cranial nerves through their various branches. Stimulation of the superior laryngeal nerve alone can produce reflex swallowing. Swallowing center is a group of neurons present in the reticular formation of the medulla oblongata. It influenced by the pre-central gyrus, amygdala, inferior frontal gyrus and inferior colliculus also. Efferent nerves – There are chiefly the hypoglossal (concerned with 1 stage); glossopharyngeal (with 2 stage) and vagus (with 2 and 3 stages) nerves. The 5, 7 and 11 cranial nerves also have some role in this process.

Peculiarities swallowing of liquid Concentration of tongue root muscles, bottom of oral cavity and soft palatinum help to fluid swallowing. Fluid enters to esophagus and after that go to the down part by help of gravity force. Speed of fluid passing of esophagus is more quickly than peristalsis of esophagus. These process need from 1 to 2 seconds. Fluid stop for a few part of second in the down part of esophagus to the time of peristalsis wave come. At these time they enter to stomach.

Role of motor function of stomach in digestive processes The motor function of the stomach is effect by contraction of the smooth muscle fibers forming its wall. Its purpose is to mix the stomach contents and to force food out of the stomach into the intestine. An important role in regulation that passage of food is played by the sphincters.

Types of peristaltic waves Two types of relatively short and recurring contractions of the muscles are distinguished. The first is encountered after a meal, when acid gastric juice is secreted. It is in fundal and caudal part of stomach. There are 3 types of waves in fundal part of stomach (peristaltic waves – with low amplitude; tonic-peristaltic – with higher duration and amplitude; tonic – which do not pass). Also there are 3 types of waves in caudal part of stomach (with low amplitude; higher amplitude and duration; series of big rythmic contraction on the phone of tonic contraction). The second type of contraction appears when food passes from the stomach into the intestine, i.e. during the so-called evacuation of the stomach, and also during the hunger contractions of an empty stomach. There are 3 types of waves: short period of strong contraction during more than 10 minutes which is change by prolong period of rest (more than one hour); middle intensive contractions which are present all time; lower contractions which are present all time.

Regulation of motor function Impulses via the vagus and sympathetic nerves are of the greatest importance to this motor activity. The vagus nerve mainly stimulates contraction (force and rate), the splanchnic nerve inhibit gastric movement. Humoral influences and chemical stimulation of the mucous membrane have a marked effect on gastric movement. The humoral agents that initiate contractions of the smooth muscles of the stomach are gastrin, histamine, choline, and potassium ions; enterogastrone, adrenaline and noradrenaline, and calcium ions inhibit gastric movements. The smooth muscles of the stomach possess automatism. The muscular coat of the stomach contains many nerve cells forming Auerbach's plexus, which apparently participates in coordination of the contractions of the various groups of muscle fibers.

Passage of food from stomach to duodenum The contractions of the gastric muscles force food from the stomach into the duodenum. The food that moves is the surface layer which passes along the lesser curvature until it reaches the pylorus, then leaves the stomach through the opening in the sphincter. The rate at which food passes into the duodenum varies according to its amount, composition, and cosistency and to the amount of gastric juice secreted. Carbohydrates are evacuated more rapidly than food rich in proteins and that more rapidly than food rich in fats. Fluids pass into the intestine almost immediately after entering the stomach.

Role of sphincters in evacuation of food from stomach to duodenum The mechanism of gastric evacuation used to be attributed to the fact that the pyloric sphincter, open in an empty stomach, periodically closes and opens during digestion. Its opening is caused by stimulation of the mucous membrane at the exit from the stomach by the HCl of gastric juice. Some food then passes into the duodenum, and turns its contents from the normal alkaline state to acid. The acid acts upon the duodenal mucosa, causing a reflex contraction of the pyloric muscles (closure of the sphincter), so arresting the passage of food from the stomach. Once the acid is neutralized by excreted juices the intestinal contents again turn alkaline and the whole process is repeated. Since alkalinity persists over a considerable interval, a new portion of food leaves the stomach after the previous one has been adequately treated. The closing of the pyloric also occurs when fats are introduced into the duodenum.

Regulation of evacuations speed of food from stomach to duodenum The following factors are of importance to the passage of food into the intestine: 1) the consistency of the gastric contents (the gastric contents enter the intestine as soon as they acquire a fluid or semifluid consistency); 2) their osmotic pressure (hypertonic solutions inhibit evacuation and leave the stomach only after they have been diluted by gastric juice to an isotonic concentration); 3) how full the duodenum is (distention of the duodenum also delays evacuation and can even cause its temporary arrest). The evacuation is controlled by the nervous system and humoral factors.

Meaning of motor function of small intestine in digestion process By help of the movements of the small intestine part of chyme mixed with juice of pancreas, bile and secretes of intestinal glands.

Characteristic of shortenings types of small intestine Three types of intestinal movements are distinguished – rythmical segmentation, pendular and peristaltic. Rythmical segmentation is a cotraction of circular muscles on the distance 1-1,5 cm which are separated one from another on the distance 15-20 cm. Pendular movement is contraction of small part of longitudinal muscles. By help of that wall of intestine change according to chyme. That is why chyme transmitted back and forward and mixing. Peristalsis movement is a circular constriction forms above a bolus of food owing to contraction of the circular muscles, while the lumen below the bolus is dilated by contraction of the longitudinal muscles. As a result, the intestinal contents move toward the widened part; then contraction of the circular muscles spreads to this part which in turn is constricted, while the segment lying below it is distended by contraction of the longitudinal musculature

Regulation of motor function of small intestine Regulation of small intestines movement may be myogenic, nervous and humoral. There are 2 pacemakers in small intestines: in the entrance place of bile and pancreatic ducts in duodenum and in ileum. The anterior hypothalamus stimulate motility, posterior – inhibit motility. Stimulate motility acethylcholine, inhibit – katecholamines, serotonine, histamine, bradikinine.

Role of motor function of big intestine in digestion process In large intestine chyme concentrated by help of absorption of water. Electrolites, water-soluble vitamins also absorbed here. In large intestine is formed fecus. Chyme is moving through all digestive tract during 2-3 days. More time it present in large intestine. 3-4 time per day strong propulsive peristalsis wave transport contents in caudal direction.

Regulation of motor function of big intestine Plants, celulose, which are bad digested, stimulate peristalsis. Parasympathetic nerves stimulate, and sympathetic nerves inhibit motor function of large intestine.