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Lecture 66

Physiology 2130 Lecture Notes - Lecture 66: Cystic Duct, Common Hepatic Duct, Urobilinogen

Course Code
Anita Woods

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Lecture 066: Secretion and motility
Bilirubin is a product from breakdown of hemoglobin
Need to be removed from the body since it is a toxic waste produce
Conjugated in hepatocytes to make it soluble and excretable
Conjugated bilirubin
Travels into the duodenum via the canalicular vessels (bile duct system) and
into the large intestine
Bacteria in the large
intestine metabolise
the conjugated
bilirubin into
Some is absorbed
into the blood and
easily excreted in the
kidney as urobilin
Most is excreted via
the intestine (along
with the rest of the
conjugated bilirubin
that was not
metabolized by
Unconjugated bilirubin
Produced by heme
Not soluble in blood
Must be carried by albumin
Caused by an increase in bilirubin (either in conjugated or unconjugated)
Only need 2-3 times more bilirubin
Obstruction (obstructive jaundice)
Prevents the movement of conjugated bilirubin into the duodenum
From gallstones in the common or hepatic duct
Not if the gallstone is in the cystic duct since the
conjugated bilirubin would not be blocked from the
Liver failure
Hepatocytes are non-functioning/reduced in function
Less conjugated bilirubin is made leading to a buildup of non-
conjugated bilirubin in the blood that can’t be secreted
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Increase hemolysis
More hemoglobin breakdown means more unconjugated bilirubin
in the blood
Look at ratio of conjugated bilirubin to unconjugated bilirubin and total bilirubin to
see what the cause might be
Can tell if it is caused by an obstruction or increased hemolysis
Jaundice in infants
Sometimes the biliary tree/canalicular vessels aren’t fully formed in
Something in breast milk cause a problem in the conjugation of bilirubin
Phototherapy (exposing skin to sun)
Allows for photoisomerization of bilirubin
Makes bilirubin more soluble and excreted by urine
Bile Salt Production
Amount changes during the day
Amount of bile salt produced and secreted by hepatocytes is controlled by how
much bile salts returns to the liver
Via hepatic portal vein
The more bile salt is returned, the more bile salt is made (feedforward)
Ilium reabsorbed bile salts for recycling
Labours process to make enough bile salt to digest meals
So lots of recycling occurs
The bile is recycled through 6-10 times during the digestion of 1 meal (which can
take 3-4 hours)
Bile solution release will increase as digestion and absorption occurs
Large amount of bile salts is needed to solubilize lipids
Not like enzymes!
Need bile to properly solubilize lipids (need to physical stay within the lipid
Neural and hormonal inputs regulates bile production, secretion and release from
Action of CCK and Secretin on the duodenal cluster
Detection of the pH, osmolarity and composition of the chyme occurs in the duodenum
Endo-enterocytes release hormones
Stimulated by the presence of protein and lipids
Act on acinar cells
Stimulate the release of enzymatic secretion
Triggers bile salt production and secretion from the liver
Trigger contractions and release of bile from the gallbladder
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