Pancreatic Secretion and the Biliary System

• What ions does the pancreas primarily secrete?

  Na+, Cl-, and HCO3-
• What are the digestive enzymes secreted by the pancreas?

  Trypsin, chymotrypsin, lipase, and amylase
• What are the protein components secreted by the pancreas?

  • Trypsinogen
  • Chymotrypsinogen
  • Procarboxypeptidase
  • Proelastase
  • Pro phospholipase A2
• How do pancreatic juice ion concentrations change at low secretion rates?

  They are closer to plasma levels.
• What happens to bicarbonate concentration at high secretion rates of pancreatic juice?

  There is an increase in bicarbonate concentration.
• What are the primary cell types involved in pancreatic secretion?

  • Ductal cells: responsible for ion secretion
  • Acinar cells: produce digestive enzymes
• What characterizes pancreatic juice at low secretion rates?

  Ion concentrations are closer to plasma levels and HCO3- concentrations are relatively low.
• What occurs at high secretion rates of pancreatic juice regarding chloride and bicarbonate concentrations?

  Chloride concentrations are lower, and bicarbonate concentrations significantly increase.
• What neutralized stomach acid

  The secretion of bicarbonate ions neutralizes the stomach acid.
• What hormone is released by the duodenum's lining in response to acidic chyme?

  Secretin
• How does bicarbonate action neutralize stomach acid?

  It mixes with chyme in the duodenum.
• What are the steps involved in the secretion of bicarbonate-rich fluid from the pancreas?

  1. Secretin is released when acidic chyme reaches the duodenum.
  2. Secretin signals the pancreas to produce bicarbonate-rich fluid.
  3. Bicarbonate mixes with chyme, neutralizing stomach acid.
  4. Bile from the liver aids in fat digestion.
• What activates pancreatic zymogens in the small intestine?

  Enterokinase (enteropeptidase) activates them.
• What is the role of enterokinase in the activation of pancreatic zymogens?

  It cleaves trypsinogen to convert it to active trypsin.
• What is the conversion of trypsinogen to trypsin?

  Trypsinogen is converted to trypsin by enterokinase.
• What are the conversions of chymotrypsinogen and procarboxypeptidases?

  Chymotrypsinogen converts to chymotrypsin; procarboxypeptidases convert to carboxypeptidases A and B.
• When is secretin primarily released?

  In response to acidic chyme entering the duodenum when pH drops below 4.5.
• What happens when secretin binds to receptors on pancreatic ductal cells?

  It triggers a signaling cascade that increases bicarbonate ion production and secretion.
• What stimulates the release of CCK?

  The presence of fats and proteins in the duodenum.
• How does CCK affect pancreatic acinar cells?

  It binds to receptors, initiating a signaling pathway that releases digestive enzymes.
• How do secretin and CCK work together in pancreatic secretion regulation?

  • Secretin stimulates bicarbonate-rich fluid production.
  • CCK stimulates enzyme secretion from acinar cells.
  • Together, they enhance pancreatic juice volume with high bicarbonate and enzyme activity.
• What role does CFTR play in pancreatic ductular secretion?

  It acts as a chloride and bicarbonate channel, facilitating ion movement across ductal epithelial cells.
• How does CFTR-mediated bicarbonate secretion affect pancreatic ductal fluid?

  It maintains a slightly alkaline pH, important for enzyme activation and function.
• What happens in patients with Cystic Fibrosis regarding pancreatic secretions?

  Defective CFTR function leads to thick, viscous secretions that obstruct ducts and impair digestion.
• What are the symptoms of malabsorption in Cystic Fibrosis patients?

  Malnutrition, abdominal pain, and greasy stools.
• What can thick meconium in newborns with cystic fibrosis lead to?

  It can obstruct the small intestine and may require surgical intervention.
• How does the autonomic nervous system regulate pancreatic secretion?

  Through the parasympathetic and sympathetic nervous systems, which have opposite effects.
• What is the role of the vagus nerve in the parasympathetic nervous system regarding the pancreas?

  It stimulates the pancreas to secrete pancreatic fluid and enzymes.
• What initiates the vagovagal reflex in the pancreas?

  The entry of chyme into the intestine.
• What do vagal efferent fibers release to stimulate pancreatic secretion?

  Acetylcholine and VIP.
• How does the sympathetic nervous system affect pancreatic secretion?

  It inhibits secretion by constricting blood vessels in the pancreas.
• What are the main components of bile secreted by the liver?

  • Water (95%)
  • Bile salts
  • Bilirubin
  • Various inorganic ions
• What is the primary function of bile salts in the small intestine?

  They help emulsify fats for digestion.
• What is bilirubin derived from?

  The breakdown of old red blood cells.
• What happens to bile when it is stored in the gallbladder?

  The water content is reduced, concentrating the bile.
• How does the concentration of bile salts and bilirubin change in the gallbladder?

  They increase, making the bile more potent for fat digestion.
• What stimulates the liver to produce more bile?

  The hormone secretin.
• What is the process of bile salt and bilirubin uptake in the liver?

  1. Taken up by hepatocytes from sinusoidal blood via specific transporters.
  2. Conjugated to become water-soluble.
  3. Secreted into bile canaliculi for excretion into bile duct.
• Why is conjugation of bile salts and bilirubin important?

  It enhances their solubility in bile for efficient excretion.
• How are bile salts taken up by hepatocytes?

  Through the sodium taurocholate co-transporting polypeptide (NTCP).