Pancreatic Secretion

• Acinus

  1. acinus releases enzymes
  2. centroacinar and ductal cells secrete aqueos HCO3-
• The exocrine pancreas is innervate dby both diision sof the ANS

  Parasympathetic > pancreatic secretion

  Sympathetic > inhibits pancreatic secretion
• There are two mechanims on the apical cell membrane for pancreatic secretion

  1. Cl- HCO3- exchanger
  2. Activation of th CFTR anion channels
• Secretin is an agonist of bicarbonate and water in the ductal cells - its effect on enzymes is mild
• CCK and Ach has a potent effect on enzyme sectrion where

  1. CCK activates afferent sensory neurons and initate a vagovagal reflex - increased enzyme synthesis
  2. Ach from parasympathetic neurons stimulate acini to secrete enzyme
• Sensory stimuli is integrated in the dorsal vagal complex of the brain with output signals transmitted to the pancreas via vagus nerve

  Both vagotomoy and atropine block the enhanced secretion during cephalic phase
• Antral destension of the stomach does not enhance pancreatic secretion
• The main amino acids stimulating CCK secretion are: phenylalanine, methionine and tryptophan
• LCFA stimulate CCK and Ach while protein and carbs hydrolysis can increase osmolality which stimulates EC cells to secrete serotonin
• CCK released in the duodenum interacts with CCK receptors on the local sensory neurons to stimulate the afferent arm of a vagovagal reflex > Dorsal vagal complex of the brain

  Vagal efferents from DVC converge on cholinergic nuerons that release Ach and VIP
• The presence of fat in the distal small intestine signals that the instestinal phase is finishing which inhibits pancreatic secretion

  Mediators are peptide YY secreted by endocrine cells of the ielum and somatostatin