The stomach and the duodenum (GB#105B03)
● Stomach movement is one way
Everyone knows that the place where the food swallowed from the mouth settles down first is the stomach. Everyone will have an image that the stomach bag shrinks or stretches and the food is kneaded together with the digestive juice until there is no more form. However, it must have been unaware that this stomach movement was a monotonous movement stuck to the model unexpectedly until studying somewhere. It seems to be one of one-way peristaltic movements from the entrance to the exit.
The mission of the stomach is to collect the things put in through the mouth and prepare for full-scale digestion and absorption in the small intestine. To that end, the stomach crushes the swallowed small and mixes it tightly together with the digestive juice (stirring).
For example, putting ingredients of dishes in a plastic bag and kneading it is also good in actual cooking. In such a case, you will mix from the top, bouncing, striking, bouncing off from the bottom or under, or with various movements to the extent that it will not be torn. Perhaps even in the stomach, many people think that they are incorporating various exercises in such a way. In the textbook, as a movement of the gastrointestinal tract, it is to learn that there are segment motions and pendulum movements in addition to peristalsis. . . . But it was not.
In short, the human gastrointestinal tract is based on one way from the mouth to the anus. The intestinal tract has many variations of movement because it is smart, but the stomach seems to be a continuation from a stiff esophagus of the head which is not that much special motor function is provided.
● Even if the movement is one way, the contents come back and forth
Since the stomach has to grind and stir food only by muscle movement, there is a unique place to say peristaltic.First, squeeze the sphincter of the “pyloric region” firmly and close the exit. Besides, the bag is slowly narrowed down from the top of the cardia, but the “fundus ventriculi” around the cardia is spreading, while gradually spreading down from the bottom part towards the pylorus, It is going down as the aperture becomes strong. Although the direction of travel is downward, the exit is closed, so even if it is peristaltic, the contents will not be sent next, but will flow back as a thin mass from the throttling gap. So, as the food clumps are crushed small, at the same time it is mixed in the bag “corpus ventriculi”.
There is no case that pulverization and stirring are completed by a single peristaltic movement and it is necessary to repeat peristaltic motion of about 3 times in about 1/2 minute over 2 to 3 hours. Sometimes the content that was kneaded fully enough by repeating its peristalsis is loosening the pylorus for a while and subdividing it into the next stage, the duodenum.
● Dangerous duodenum
“Gastrointestinal” is said in a bite. It seems that there are many cases in which it is handled together with gastroduodenal a little more finely.However, as a gastrointestinal tract, although it is a continuation, can you really connect the stomach and the duodenum? The more you worry, the inside of each bag is a different world. In the stomach, a large amount of hydrochloric acid is secreted, it is extremely acidic, it kills bacteria entering from the mouth and destroys the food cells and breaks down the protein. Approximately pH 1.7 on an empty stomach, it seems to be slightly diluted when food enters, but still pH 2 to 4. As the cells are bare, they are melted quickly so the stomach walls are protected with a special thick mucus layer. The stomach does not have the intention of absorbing nutrients broken down, so it may be OK. Absorption of nutrients is the role of the small intestine to follow.
Digestion absorption in the small intestine is done in neutral or weakly alkaline environment. The place of switching from strongly acidic to weakly alkaline between this stomach and small intestine is the duodenum, especially at the entrance, the duodenal bulb is subjected to the most severe change. Every time the contents from the stomach comes in, the ball changes suddenly to acidity (pH 2) and the large fluctuating returning to neutrality immediately repeats. A weakly alkaline mucus is secreted in large quantities against hydrochloric acid from the specially developed secretory gland called Brunner glands to protect the ball and the duodenum following it. Furthermore, the pancreatic juice containing digestive enzymes that comes from duodenal papilla in the middle of the duodenum is almost a solution of bicarbonate ion （HCO3–） exceeding 100 mEq/L. This solution (pH 8) works to stabilize the neutral to weakly alkaline environment in the duodenum. Unlike the stomach, there are reverse peristalsis in the duodenum, so this may also serve to prevent the acid substances of the stomach from spreading throughout the duodenum.
● The gastrointestinal tract moves even if it is empty
Gastrointestinal movement is for digesting food by digesting it, so it seems that when the stomach is empty it is resting a bit and it will start moving with food as the food approaches. Rather, it is said that when there is no content it is relatively constantly repeating the routine contraction movement.A couple of hours after having a meal, once the gastrointestinal tract has become empty, movement stops once, but after a while the stomach and duodenum start irregular movement again. After that, it gradually became to repeat strong regular shrinkage and relaxation, and gradually became quiet.
The set of this movement of 90 minutes in total is said to repeat it many times until the next meal comes. This movement seems to be pretty strongly contracting, with a good name interdigestive migrating motor complex (IMMC) in English. Many people would think what the stomach is doing though the contents are empty. Perhaps it is said that they are cleaning the gastrointestinal walls by using the empty time to sweep away the germs and bacteria.
● The stomach does not reflux on its own
It is often said that the stomach regurgitates, but even if the condition gets worse, the stomach can only move one way. However, in fact, when you vomit you will come out inside the stomach. Actually, it is not the reverse peristalsis of the stomach itself, but it seems to have forcibly pushed the contents out by crushing the stomach from the outside with the abdominal muscles and the diaphragm.
○ Referenced sites
· For those who want to know more about the workings of the stomach and duodenum
⇒ Stomach science(Provided by Eisai)
⇒ Abdominal bloating feeling, bellyng (Dr Miyake ‘s family medicine)(← About the movement of the stomach)
⇒ Measurement of pH in upper gastrointestinal tract and its clinical significance (Tokyo Jikei University Medical School · Professor Watanuki)
⇒ Study on the relation between human gastroduodenal movement and ph in duodenum (Gunma University 1st Internal Medicine)
⇒ Anatomical physiology 17 episode “digestive organ” (Tama sensei class)
○ Related articles
◆ Absorption of carbohydratel
◆ Glucose and the hydrolysis of sucrose
◆ Smooth muscle contraction
◆ Switching of the airway and esophagus (GB#105A04)
◆ 分節運動 intestinal segmentation
◆ Peptide bond
◆ Digestion and metabolism
◆ Acetylcholine receptors (GB#114B03)
○ Referenced books
・臓単―ギリシャ語・ラテン語 (語源から覚える解剖学英単語集 (内臓編))
・カラー図解 人体の正常構造と機能 全10巻縮刷版，坂井 建雄，日本医事新報社
・細胞の分子生物学， ニュートンプレス; 第5版 (2010/01)
rev.2010719, rev.20150315, rev.20170211,rev.20170505，rev.20170518, rev.20180430.KISO-IGAKU-KYOIKU-KENKYUKAI(KIKKEN)