Serotonin - Serotonin (English spelling)

A chemical transmitter (neurotransmitter) that is synthesized during the metabolism of the essential amino acid tryptophan in the body. In mammals, it is found in platelets, the mucous membrane of the small intestine, and the brain and nervous system. Most of it is found in enterochromaffin cells (EC) in the mucous membrane of the small intestine, and it is involved in the function of the digestive tract, including intestinal peristalsis. Excessive secretion of serotonin in the digestive tract causes diarrhea, while a deficiency causes constipation. In addition to these bowel movements, serotonin is also involved in the symptoms of irritable bowel syndrome, which is accompanied by abdominal pain and discomfort. Serotonin in the blood is taken up by platelets and circulates throughout the body, exerting a blood clotting effect (hemostasis effect) that clots blood and forms platelet clots, as well as a vasoconstriction effect. It is said that migraines occur when cerebral blood vessels constrict and then expand, but there are many theories about the causes of migraines.

Serotonin, which is present in the nervous system, is involved in regulating the lack of dopamine, which is said to be the cause of depression, and acts to stabilize the mind and body. Therefore, if stress or other factors cause a lack of serotonin, mental stability cannot be maintained, leading to depression and insomnia. In addition to sleep, serotonin is also involved in biological rhythms and temperature regulation.

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Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

必須アミノ酸のトリプトファンが体内で代謝される過程で生合成される化学伝達物質（神経伝達物質）。哺乳(ほにゅう)動物では、血小板中や小腸粘膜および脳神経系に存在する。多くは小腸粘膜にある腸クロム親和性細胞（EC：enterochromaffin cell）に存在し、腸の蠕動(ぜんどう)運動をはじめ消化管の働きにかかわる。消化管でセロトニンが過剰に分泌されると下痢に、不足すれば便秘となり、こうした便通異常のほか腹痛や腹部の不快感を伴う過敏性腸症候群の症状にも関与する。血中のセロトニンは血小板に取り込まれて体内をめぐり、血液を凝固させ血小板血栓を形成する血液凝固作用（止血作用）や血管収縮作用などを示す。血管収縮作用に関して、脳血管が収縮したのち拡張すると片頭痛がおこるともされるが、片頭痛の原因には諸説が多い。

　脳神経系に存在するセロトニンは、うつの原因ともされるドーパミン不足の調節に関与し、心身を安定させるように働く。したがって、ストレスなどが原因でセロトニン不足が生じると精神の安定が保てず、うつ病や不眠症などになる。また、睡眠のほか、生体リズムや体温調節などにもかかわっている。

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