Physiology 2130 Lecture Notes - Lecture 66: Cystic Duct, Common Hepatic Duct, Urobilinogen
1 May 2018
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Lecture 066: Secretion and motility
Bilirubin
● 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
urobilinogen
● Urobilinogen
○ 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
bacteria)
● Unconjugated bilirubin
○ Produced by heme
○ Not soluble in blood
■ Must be carried by albumin
● Jaundice
○ Caused by an increase in bilirubin (either in conjugated or unconjugated)
■ Only need 2-3 times more bilirubin
○ Causes
■ 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
duodenum
■ 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
find more resources at oneclass.com
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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
■ Temporary
■ Sometimes the biliary tree/canalicular vessels aren’t fully formed in
infants
■ Something in breast milk cause a problem in the conjugation of bilirubin
■ Treatment
● 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
droplets)
● Neural and hormonal inputs regulates bile production, secretion and release from
gallbladder
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
○ CCK
■ 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
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
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. 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 urobilinogen. 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 bacteria) Caused by an increase in bilirubin (either in conjugated or unconjugated) 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 duodenum. Less conjugated bilirubin is made leading to a buildup of non- conjugated bilirubin in the blood that can"t be secreted.
