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某些肽类既存在于胃肠道,也存在于脑和外周神经中,这一现象表明,在神经和胃肠道产生肽类的细胞之间,可能存在着某种起源上和功能上的密切关系。在胃肠道活动的调节上,肽类可能通过四种途径起作用。(1)作为激素,由内分泌细胞释放入血循环,作用于远处的靶细胞;(2)由胃肠道粘膜中的内分泌样细胞释放后,通过局部扩散,作用于邻近的细胞;(3)由神经末梢释放入血循环,即神经内分泌机能;(4)作为神经递质,由神经轴突释放,经过突触间隙而作用于接受神经冲动的细胞上。
Some of the peptides are present in the gastrointestinal tract as well as in the brain and peripheral nerves, a phenomenon that suggests that there may be some originally and functionally close among neurogenic and gastrointestinal-producing cells relationship. In the regulation of gastrointestinal activities, peptides may play a role in four ways. (1) as hormones released by endocrine cells into the blood circulation and acting on target cells in the distance; (2) local secretion by endocrine cells in gastrointestinal mucosa, acting on adjacent cells; (3) Release from the nerve endings into the blood circulation, that is, neuroendocrine function; (4) as a neurotransmitter, released by the axons, through the synaptic cleft and acting on the nerve impulses on the cells.