Key Points

• Saliva is produced in large volumes relative to the weight of the glands, contains relatively high concentrations of K+, is hypotonic, and contains specialized organic substances.

• Acini produce the primary saliva, containing water and electrolytes in concentrations approximately equal to those of plasma.

• Gastric acid is secreted in concentrations as high as 150 mmol/L by the parietal cells, which contain a proton pump (H+,K+-ATPase) in their apical membranes. Acid converts inactive pepsinogen to pepsin, solubilizes some food, and kills bacteria.

• The major stimulants of acid secretion are the hormone gastrin, the vagal mediator acetylcho-line, and histamine, which is released from the enterochromaffin-like (ECL) cells by gastrin and acetylcholine and acts as a paracrine to stimulate the parietal cells.

• The cephalic phase of gastric secretion is mediated by the vagus nerve, which stimulates the parietal cell via acetylcholine and releases

Essential Medical Physiology, Third Edition

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