Gastro-intestinal tract, hormones

G68. Gregory, R. A., Gastric secretion A review of its chief nervous and hormonal mechanisms. In Surgical Physiology of the Gastro-Intestinal Tract (A. N. Smith, ed.), pp. 57-70. Roy. Coll. Surg., Edinburgh, 1962. 

Serotonin acts as neurotransmitter in the brain of animals (E 3.2). It is, however, also of importance as a hormone for the maintenance of normal gut mobility in the gastro-intestinal tract (E 3.1). Serotonin accumulates in the trichomal fluid of the stinging nettle (Urtica dioica) which is injected into the body of animals breaking the hairs during predation of even touching. In addition to the other constituents of the nettle toxin, e.g., acetylcholine and histamine, it provides protection against predation (E 5.5.3). 5-Hydroxy-L-tryptophan and serotonin accumulate in the seeds and fruits of several plant species, e.g., bananas, pineapples, tomatoes and walnuts. At least in walnut seeds serotonin serves in the detoxication of ammonia during maturation and abscission of the fruits (E 2.2). 

The Hormones of the Gastro-Intestinal Tract excite the digestive glands. The foUow-... 

Little is known about the biochemical mechanism of vitamin D action. It promotes the absorption of Ca++-ions in the gastro-intestinal tract and influences the metabolism of bone tissue. Deficiency of vitamin D results in the clinical syndrome rachitis (also in animal experiments), characterized by a softenii (inadequate calcification) of the bones. Excessive administration of vitamin D produces a hyper-vitaminosis, during which calcium is again mobilized out of the bone structure this hypervitaminosis resembles the action of the parathyroid hormone. 

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