The regulation of acid and pepsin secretion reflects an intricate balance of chemotransmitters delivered to the gastric mucosa by several pathways that mediate both stimulatory and inhibitory mechanisms . Similarly, several mechanisms contribute to the remarkable ability of normal gastroduodenal mucosa to defend itself against injury from the acid/peptic activity in gastric juice and to rapidly repair injury when it does occur. Secretory, defense, and healing mechanisms are regulated by the same type of overlapping neural, endocrine, paracrine, and autocrine control pathways.
The numerous stimulators and inhibitors of each regulated element suggest redundant control; however, there is limited understanding of the actual physiologic and pathophysiologic importance of most of these pathways and chemotransmitters. The problem is that there remains a limited set of pharmacologic and molecular biologic tools to dissect the significance of each pathway.
Although gastric acid is not essential for life, the universal preservation of gastric acid secretion among vertebrates indicates critical evolutionary advantage. The benefits of gastric acid are to facilitate digestion of proteins and the absorption of calcium, iron, and vitamin B12. It also suppresses growth of bacteria, which can help prevent enteric infections and small intestinal bacterial overgrowth.
PHASES OF ACID SECRETION
The physiologic stimulation of acid secretion has classically been divided into three interrelated phases: cephalic, gastric, and intestinal .
●The cephalic phase is activated by the thought, taste, smell and sight of food, and swallowing. It is mediated mostly by cholinergic/vagal mechanisms.