Chapter 46: Hepatobiliary Function

The discussion encompasses salivary, gastric, and pancreatic secretions, each serving distinct roles in preparing food for absorption while maintaining the integrity of the gastrointestinal tract. Salivary secretion involves acinar cells that produce enzyme-rich fluid containing amylase and lipase, which undergoes modification in the ducts to regulate electrolyte balance and osmolarity. The autonomic nervous system provides nearly complete control of salivary secretion through parasympathetic and sympathetic pathways. Gastric secretion involves three specialized cell types: parietal cells generate hydrochloric acid through H+/K+-ATPase pump activity, chief cells release pepsinogen as an inactive precursor of the proteolytic enzyme pepsin, and mucous cells secrete mucus and bicarbonate that protect the gastric mucosa. Gastric acid secretion occurs in three coordinated phases—cephalic, initiated by sensory and cognitive stimuli; gastric, triggered by mechanical and chemical stimulation of the stomach; and intestinal, modulated by nutrient entry into the duodenum. Multiple regulatory factors influence acid production, including the hormone gastrin, neurotransmitter acetylcholine, paracrine mediator histamine, and inhibitory hormone somatostatin that provides negative feedback. Pancreatic secretion comprises acinar cells that release digestive enzymes and ductal cells that secrete bicarbonate-rich fluid, both controlled by the hormones secretin and cholecystokinin. The chapter integrates neural, hormonal, and cellular mechanisms to illustrate how coordinated secretory responses support effective nutrient digestion and mucosal protection. Clinical applications include peptic ulcer disease pathophysiology, Zollinger-Ellison syndrome from gastrin-secreting tumors, cystic fibrosis affecting pancreatic function, and chronic pancreatitis involving enzyme insufficiency and inflammation.