Pancreatic Secretion Is Phasic

The regulation of pancreatic secretion by various hormonal and neural factors is summarized in Table 27.4. Seeing, smelling, tasting, chewing, swallowing, or thinking about food results in the secretion of a pancreatic juice rich in enzymes. In this cephalic phase, stimulation of pancreatic secretion is mainly mediated by direct efferent impulses sent by vagal centers in the brain to the pancreas and, to a minor extent, by the indirect effect of parasympathetic stimulation of gastrin release. The gastric phase is initiated when food enters the stomach and distends it. Pancreatic secretion is then stimulated by vago-vagal reflex. Gastrin may also be involved in this phase.

During the most important phase, the intestinal phase, the entry of acidic chyme from the stomach into the small intestine stimulates the release of secretin by the S cells (a type of endocrine cell) in the intestinal mucosa. When the pH of the lumen in the duodenum decreases, the secretin concentration in plasma increases. This response is followed by an increase in HCO3~ output by the pancreas. The secretion of pancreatic enzymes is increased by circulating CCK and by parasympathetic stimulation through a vago-vagal reflex. The release of CCK by the I cells (a type of endocrine cell) in the intestinal mucosa is stimulated by exposure of the intestinal mucosa to long-chain fatty acids (lipid digestion products) and free amino acids.

Interstitial

Duct lumen

HCO3

Duct lumen

HCO3

Interstitial

Cystic Fibrosis Intestinal

A model for electrolyte secretion by pancreatic duct cells. The luminal membrane Cl_ channel is CFTR (cystic fibrosis transmembrane conductance regulator).

^ABLE 27.3^ Characteristics of Pancreatic Enzymes

Enzyme

Specific Hydrolytic Activity

Proteolytic

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Responses

  • marco
    How is hco3 produced in the pancreas?
    6 years ago

Post a comment