Bile, gallbladder and gallstones Flashcards
What is the gallbladder for?
→Storage and concentration of bile
Why is bile concentrated?
→Concentrated because of active Na+ transport and H2O from the gallbladder
How does the pH of bile become acidic?
→pH of bile drops and becomes acidic as Na+ is exchanged for H+
What is pancreatic juice made from?
→ bile salts
→bile pigments
→dissolved substances in alkaline electrolytes
→ some come from the gallbladder and some come from the pancreas
Where is water added to bile?
→Water is added via specific tight junctions within ductules
What do the ductules do?
→The ductules scavenge glucose, amino acids
→GSH is hydrolyzed
What do ductules secrete and in response to what?
→ IgA (mucosal protection)
→HCO3-
→ H2O
→in response to secretin in the postprandial period
Describe the flow of bile
Hepatocytes
↓
Bile canaliculi (merge to form ductules)
↓
Terminal bile ducts
↓
Hepatic ducts (left and right)
↓
Common bile ductWhat 2 cell types secrete bile?
→Hepatocytes
→ Epithelial cells of bile ducts
What components of bile do hepatocytes secrete?
→cholesterol
→lecithin
→bile acids
→ bile pigments (bilirubin, biliverdin, urobilin)
What components of bile do epithelial cells secrete?
→ bicarbonate-rich salt solution
What does secretin influence?
→influences the secretion of bicarbonate rich salt solutions and H2O
When is secretion of bile the greatest?
→greatest during and after a meal
What does increased bile salt concentration in the blood mean?
→ ↑ bile salt secretion into bile canaliculi
When does the sphincter of Oddi contract?
→ during periods of fasting
When does the sphincter of Oddi relax?
→ relaxes during and after meals.
What are the substances secreted across the canalicular membrane?
→ Bile acids → Phosphatidylcholine → Conjugated bilirubin → Cholesterol → Xenobiotics
What substances enter the bile via diffusion?
→water → glucose →Ca2+ → GSH →amino acids → urea
What is the composition of hepatic bile?
→97% water →cholesterol → lecithin → bile acids → bile pigments
What is the composition of gall bladder bile?
→89% water →HCO3- →Cl- →Ca2+ → Mg2+ →Na+ →cholesterol →bilirubin → bile salts
How many pathways are there for bile formation?
→ 2
What does bile do to cholesterol levels?
→ bile comes from cholesterol so bile formation reduces cholesterol levels.
What acids are formed from the neutral pathway and in what amounts?
→cholic acid
→ chenodeoxycholic acid
What are primary acid bile salts?
→cholic acid
→ chenodeoxycholic acid
What are bile acids made from?
→ Cholesterol
What are bile acids conjugated with?
→Glycine
→ Taurine
What does conjugation do to bile acids?
→Conjugation helps to increase the ability of bile acids to be secreted and reabsorbed and decreases their cytotoxicity
What are the 4 major bile acids present in humans and in what amounts are they present in?
→Cholic acid: 50% = quantitatively more important
→Chenodeoxycholic acid: 30%
→Deoxycholic acid: 15%
→Lithocholic acid: 5%
Where are secondary bile acids formed?
→ In the colon
What are secondary bile acids?
→Deoxycholic acid
→Ursodeoxycholic acid
What are the conversions that intestinal bacteria do?
→Chenodeoxycholic acid → Lithocholic acid and Ursodeoxycholic acid
→Cholic acid → Deoxycholic acid
What are the main functions of bile acids ?
→Elimination of cholesterol to bile acids (5% excreted in feces)
→ Reduce the precipitation of cholesterol in the gallbladder, bile acids and phospholipids help solubilize cholesterol in the bile
→Facilitate the absorption of fat soluble vitamins A,D,E,K
→Regulate their own transport and metabolism via enterohepatic circulation
→Facilitate the digestion of triglycerides
What activates the cephalic phase?
→taste
→ smell
→presence of food in mouth
What activates the gastric phase?
→distension of stomach generates impulses in vagus nerve
What does the gallbladder do during the intestinal phase?
→period of most gallbladder emptying
What does CCK cause?
→causes contraction of the gallbladder and relaxes the sphincter of Oddi
How is bile secreted into the duodenum?
→Distension of the duodenum triggers vagal innervation
→Afferent impulses are sent to the DVC
→They send the vagal efferent signal which produces ACh
→CCK and secretin are secreted
→CCK causes contraction of the gallbladder
What causes the Sphincter of Oddi to relax?
→NO and VIP cause the sphincter of Oddi to relax
Where are bile salts and lecithin synthesized?
→ In the liver
What neutralizes acids in the duodenum?
→HCO3- and other ions
How are most bile salts reabsorbed?
→by Na+-bile salt coupled transporters
How does the process of bile salt recycling occur and what is this called?
→Returned to the liver and secreted again into bile
→Recycling pathway from intestine to liver and back - →enterohepatic circulation
What does the liver secrete into the bile and how is this eliminated?
→ cholesterol
→ eliminated in feces
What does interruption of enterohepatic circulation cause?
→Excess synthesis of bile salts by the liver
→Kidneys will excrete the synthesized bile and some cholesterol
What are gallstones made from?
→Bile salts (bile compounded with a cation Na+) cholesterol and phospholipids
What does a high cholesterol content of bile do?
→The higher the cholesterol content of bile the greater the concentrations of phospholipid and bile salts.
What causes increased cholesterol?
→Liver secretes excess
→Reabsorption of salt and water
→Cholesterol crystallizes and forms gallstones
→Precipitation of bile pigments
What are the 2 types of gallstones?
→Cholesterol stones (85%) : obesity
→Calcium bilirubinate stones - due to increased conjugated bilirubin
What are the factors involved in gallstone formation?
→Bile stasis
→Decreased amount of bile acids due to malabsorption
→Chronic infection
→Supersaturation of bile with cholesterol
→Nucleation factors or glycoproteins
What is bile stasis?
→stones form in bile that is sequestered in gallbladder rather than bile that is flowing in bile ducts into duodenum
How is the gallbladder blocked in cystic fibrosis?
→cystic fibrosis gallbladder and cystic ducts can be blocked by thick mucus
How do small gallstones pass?
→ easy passage via bile duct
How do large gallstones pass?
→lodge in opening of gallbladder
duct from the pancreas joins bile ducts before it joins the duodenum
What does lodging of gallstones cause?
→stoppage of bile and pancreatic secretions
What are the symptoms of gallstones?
→‘Upper right quadrant pain’
→Pressure build up causes decreased secretion of bile
→Jaundice
What are the 3 diagnostic methods used for gallstones?
→Ultrasonography and CT
→Cholescintigraphy
→ERCP
What is cholescintigraphy?
→ Getting an image of the bile ducts using technetium
What is ultrasonography and CT for?
→explore the upper right quadrant of gallbladder to detect gallstones
What is ERCP used for?
→Visualize the biliary tree by injecting contrast media from endoscope channel
→Insert device and remove gallstone fragments that may be obstructing bile flow
What do gallstones that impact the common bile duct cause ?
→Obstruction of bile flow
→Cholestatic jaundice which can cause bacterial infections
What does the gallbladder do if it is inflamed?
→secrete mucus if inflamed and rupture
What can occur as a result of infections?
→Fevers can occur as a result of infections
