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Gastrointestinal > Bile, Gallbladder and Gallstones > Flashcards

Bile, Gallbladder and Gallstones Flashcards

1
Q

What is the function of the gallbladder?

A

Storage and concentration of bile

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2
Q

Why is bile so concentrated and acidic in the gallbladder?

A

Concentrated because of active Na+ transport (and H2O) from gallbladder
The pH of bile drops (becomes “acidic”) as Na+ is exchanged for H+

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3
Q

What is the composition of pancreatic juice?

A

bile salts, bile pigments and dissolved substances in alkaline electrolytes

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4
Q

When does bile move to the gallbladder?

A

between meals

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5
Q

When is bile modified?

A 
Bile → larger ductules and ducts (composition is modified)
Water is (may be) added via specific tight junctions within ductules (cholangiocytes)
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6
Q

What is the purpose of bile travelling through so many ducts and ductules?

A

The ductules scavenge glucose, amino acids; GSH is hydrolysed
Ductules secrete IgA (mucosal protection), HCO3- and H2O in response to secretin in the postprandial period

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7
Q

Outline the flow of bile

A 
Hepatocytes
     ↓
Bile canaliculi (merge to form ductules)
       ↓
Terminal bile ducts
      ↓
Hepatic ducts (left and right)
      ↓
Common bile duct
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8
Q

What are the 2 types of cells secreting bile components?

A

Hepatocytes

Epithelial cells of bile ducts

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9
Q

Which components of bile do hepatocytes secrete?

A

cholesterol, lecithin, bile acids, bile pigments (bilirubin, biliverdin, urobilin, etc.)

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10
Q

What components of bile is secreted via epithelial cells of the bile ducts?

A

bicarbonate-rich salt solution

Secretin influences the secretion of bicarbonate-rich salt solutions and H2O

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11
Q

When is bile secretion the greatest?

A

Secretion of bile is greatest during and after a meal
Increased [bile salt]blood causes ↑ bile salt secretion into bile canaliculi
Increased secretion leads to ↑flow of bile

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12
Q

Explain the motility of the sphincter of Oddi during and after meals

A

Sphincter of Oddi contracts during periods of fasting

Sphincter of Oddi relaxes during and after meals due to vagal innervation & CCK

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13
Q

Which substances cross the bile canalicular membrane?

A 
Bile acids
Phosphatidylcholine
Conjugated bilirubin
Cholesterol
Xenobiotics (foreign chemicals/substances, e.g. drugs)
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14
Q

How are substances transported across the canlicular membrane?

A

Specific transporters ferry substnces into bile

Substances such as water, glucose, Ca2+, GSH, amino acids and urea enter the bile by diffusion

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15
Q

What is the composition of hepatic bile?

A

97% water; cholesterol, lecithin, bile acids, bile pigments, etc.

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16
Q

Describe the composition of gallbladder bile

A

89% water; HCO3-, Cl-, Ca2+, Mg2+, Na+, cholesterol, bilirubin, bile salts, etc.

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17
Q

Where is bile synthesised and transported to?

A

Bile synthesised in liver → cross canalicular membrane → bile canaliculi → gallbladder

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18
Q

Explain the movement of bile to the gallbladder

A

Bile concentrated in gallbladder (NaCl and H2O loss → increased solid content)
Bile goes to the gallbladder between meals when sphincter of Oddi is closed

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19
Q

What are bile acids made from?

A

cholesterol

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20
Q

Explain the significance of bile acids in bile

A

Secreted into bile and conjugated to glycine or taurine

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21
Q

What is the purpose of conjugating bile acids?

A

Conjugation helps to increase the ability of bile acids to be secreted (more soluble) and also decreases their cytotoxicity

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22
Q

How many bile acids are there?

A

There are 4 major bile acids found in humans:

  • Cholic acid: 50% = quantitatively more important
  • Chenodeoxycholic acid: 30%
  • Deoxycholic acid: 15%
  • Lithocholic acid: 5%
  • primary bile acids formed in liver
  • secondary bile acids formed in colon
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23
Q

How do bile acids affect cholesterol in the body?

A

Elimination of cholesterol to bile acids (5% excreted in faeces)

Synthesis + excretion of bile acids in faeces is a significant mechanism for excess cholesterol elimination

Reduces cholesterol precipitation in gallbladder; bile acids + phospholipids help solubilise cholesterol in bile

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24
Q

How do bile acids affect vitamins in the body?

A

Facilitate the absorption of fat-soluble vitamins (ADEK)

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25
Q

What affect do bile acids have on dietary fats?

A

Facilitate the digestion of triglycerides - work in concert with phospholipids (licithin) and monoglycerides to ensure the emulsification of fats
Facilitate the digestion of dietary fats by acting as emulsifying agents that render fats accessible to pancreatic lipases

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26
Q

What is the significance of bile acids?

A

Regulate their own transport and metabolism via enterohepatic circulation

27
Q

Explain the stages of gallbladder contraction

A

Cephalic, Gastric and intestinal

28
Q

Explain what occurs in the gallbladder during the cephalic phase

A

taste, smell and presence of food in the mouth → impulses via vagus nerve

29
Q

What happens during the gastric phase?

A

distension of stomach generates impulses in vagus nerve

30
Q

What effect does the intestinal phase have on the gallbladder?

A

Period of most gallbladder emptying; key mediators for increased release are
CCK in response to lipids → secrete bile to emulsify fat for digestion by pancreatic lipases

=> causes gallbladder contraction
=> sphincter of Oddi relaxtation

Secretin in response to high acidity - stimulates duct cells

31
Q

What is the role of the vagus nerve in the GI tract?

A

Vagus nerve (VIP/NO) - conveys information of contents of the duodenum to the CNS

32
Q

Outline the mechanism of bile secretion into the duodenum

A
  1. Nutrients in duodenum sends vagal afferent signals to
    DVN
  2. Vagal efferent from DVN releases ACh at gallbladder
  3. Nutrients in duodenum stimulate release of CCK via
    bloodstream
  4. ACh + CCK cause smooth muscle contraction
33
Q

What effect does motilin have on gallbladder?

A

Motilin induces gallbladder emptying and antral contractions in the fasting state

34
Q

How is gallbladder contraction regulated?

A

Via CCK - fatty meals stimulates CCK release

=> sphincter of Oddi relaxes
=> gallbladder contracts
=> increased bile flow to duodenum via common bile duct

35
Q

What components of enterohepatic circulation are synthesised in the liver?

A

Bile salts, lecithin (phospholipids)

36
Q

What is the role of HCO₃⁻ and other ions?

A

neutralise acids in duodenum

37
Q

What is enetrohepatic circulation?

A

Most bile salts are reabsorbed by Na+-bile salt coupled transporters

The bile salts are returned to the liver and secreted again into bile

The recycling pathway from intestine to liver and back to intestine = enterohepatic circulation

38
Q

How much bile is recycled via enterohepatic circulation?

A

Body’s content of bile acid pool (~3.5g) may be recycled ~twice per meal

39
Q

What happens to cholesterol in enterohepatic circulation?

A

Liver also secretes cholesterol in the bile and some of this is excreted in faeces

40
Q

What is the consequence of enterohepatic circulation interruption?

A

Interruption of enterohepatic circulation (e.g. after ileal resection) will cause the following:

  • Excess synthesis of bile salts by the liver
  • Kidneys will excrete synthesised bile salts (+ some
    Cholesterol)
41
Q

What are gallstones (cholelithiasis)?

A

small stones, usually made of cholesterol, that form in the gallbladder

42
Q

What is the prevalence of gallstones in women and men?

A

Ratio of incidence of gallstones = 2:1 in women and men, respectively and incidence increases with age

43
Q

How does cholesterol affect bile salts?

A

The higher the cholesterol content of bile, the greater the concentrations of phospholipid and bile salts

Bile salts (bile compounded with a cation, e.g. Na+), cholesterol and phospholipids

44
Q

What can cause excess cholesterol?

A

Liver secretes excess

Reabsorption of salt and water

45
Q

What is teh consequence of excess bile pigments and cholesterol?

A

The cholesterol crystallises and forms gallstones; Supersaturation of bile with cholesterol
Precipitation of bile pigments

46
Q

What are the 2 types of gallstones?

A 
Cholesterol stones (85%): 
- obesity; ↓ bile acids vs ↓ phospholipids

Calcium bilirubinate stones:
- due to ↑conjugated bilirubin (associated with haemolytic
anaemia)

47
Q

How does bile stasis contribute to gallstones?

A

Bile stasis: stones form in bile that is sequestered in the gallbladder rather than bile that is flowing in the bile ducts into the duodenum

48
Q

Explain how problems with bile production can lead to gallstone formation

A

Decreased amount of bile acids due to malabsorption (in cystic fibrosis – dehydrated and acidic; 10% higher incidence); problems with bile production

49
Q

How does infection contribute to gallstones?

A

Chronic infection – bacteria help in the formation of pigment stones

50
Q

How does size of gallstone affect their location?

A

Small gallstones have easy passage via bile duct

Larger gallstones lodge in the opening of the gallbladder

51
Q

How can gallstones cause nutritional deficiency?

A

Duct from pancreas joins bile duct before it joins the duodenum
Lodging of gallstones at this point causes stoppage of bile + pancreatic secretions (pressure builds up)
Consequence →nutritional deficiency

52
Q

How do gallstones lodged in bile duct cause decreased bile secretion?

A

Further pressure build up causes decreased secretion of bile

53
Q

What causes jaundice?

A

Increased accumulation of bilirubin in blood

54
Q

How would we know a patient had gallstones?

A

People complain of upper right quadrant pain

55
Q

What pigments are present in bile, urine and faeces?

A

Bile is yellow because of bilirubin
Urine colour due to uribin
Stercobilin colours faeces

56
Q

How would we diagnose gallstones?

A

Ultrasonography and computer tomography:

Cholescintigraphy:

Endoscopic retrograde cholangiopancreatography (ERCP):

57
Q

Explain how ultrasonography can help detect gallstones?

A

explore the right upper quadrant of gallbladder to detect gallstones

58
Q

How does cholescintigraphy diagnose gallstones?

A

administer technetium-99m-labelled derivative of iminodiacetic acid (radioactive tracer)
→ images of gallbladder and ducts

59
Q

Explain how you would carry out an ERCP

A

Allows us to visualise biliary tree by injecting contrast media from an endoscope channel

Insert device(s) and remove gallstone fragments that may be obstructing the bile flow, pancreatic juice or both

60
Q

What are the symptoms of gallstones in the cystic bile duct?

A

painful gallbladder contractions

61
Q

What symptoms would prevail in patients with gallstones blocking the common bile duct?

A

pain and nausea
lack of bile release
failure to excrete bilirubin = jaundice

62
Q

What is the effect of a gallstone blocking duodenal papilla?

A 
inappropriate activation of pancreatic zymogens 
acute pancreatitis (hard to differentiate from appendicitis)
63
Q

How will the gallbladder respond to inflammation?

A

Gallbladder will secrete mucus if inflamed and rupture (mucocele or hydrops) - very painful can cause sites of infections

64
Q

Where are the majority of gallstones found?

A

85% of cases are asymptomatic (gallstones remain in gallbladder)

Gastrointestinal (18 decks)

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