GI 3: Digestion And Absorption: Bile Acids And Bile Pigments

Question 0

Bile acids (salts)
Are made by the?
Are absorbed in the?
The remaining part this isn’t reabsorbed passes into?

Answer 0

• made by the liver
• 90% of bile acids are absorbed in the terminal ileum then travel via portal blood back to liver where they can be re-secreted into bile “enterohepatic circulation”
• the remaining 10% of bile acids that aren’t reabsorbed pass into the large intestine and are modified by bacteria

Question 1

What is the composition of bile? What’s in it?

Answer 1

• electrolytes
• bile salts/acids important role in lipid digestion and cholesterol excretion
• phospholipid
• excretion products eg cholesterol, bilirubin, drugs
• water

Question 2

How does bile function to aid lipid digestion?

Answer 2

• allow greater effect of pancreatic lipase by emulsification➡ increased fat globule SA➡ increases oil-water interface were lipase can act
• aids absorptive process by formation of micelles- allow fat digestion products to cross enterocyte membrane

Question 3

How does bile also act as a route of cholesterol excretion?

Answer 3

• cholesterol of oxidised in the liver into 7-hydroxycholestrol
• 7-hydroxycholestrol is then converted into the two primary bile acids via several step I don’t have to know thank god

Question 4

There are primary and secondary bile acids. Describe them both

Answer 4

Primary bile acids are produced by the liver

• bile acids that aren’t reabsorbed in the terminal ileum and recycled pass into the large intestine and are modified to the secondary bile acids by bacteria
• the glycine and taurine residues from secondary bile acids are removed and are either reabsorbed by the gut and returned to the liver or excreted

Question 10

Bile pigments are generated by the?
What do they do?
What is the clinical important of bile pigments?

Answer 10

Bile pigments are generated by the reticulo-endothelial system and the liver.
The facilitate the removal of toxic bilirubin
-turnover if the RBC and cytochromes results in production of heme
-degradation of the heme ring results in iron being recycled and the production of biliverdin (and bilirubin)
Clinical importance of bile pigments:
1. Hyperbilirubinaemia= high levels of bilirubin circulating in the blood, these high levels can be toxic to the CNS
Treatment: UV light
-the amount of conjugated and free bilirubin in the circulation can provide some indication to whether they have hyper…

2. Liver damage:
   - damaged liver may have poor ability to conjugate bilirubin
   - you typically observe increase in circulating free bilirubin
   - an increase in conjugated bilirubin may be observed if the cell damage results in leakage into plasma, but the increase in conjugated bilirubin is usually less than free bilirubin.

Hemolysis: breakdown of erythrocytes

• there are many diseases and toxins associated with haemolysis
• haemolysis can result in elevation of circulating bilirubin➡ this is usually observed as an increase in free bilirubin because the liver is struggling to keep up with processing the amount of bilirubin being produced.

Jaundice in neonates:

• erythrocyte breakdown results in production of free bilirubin
• immature liver has reduced ability of UDP glucuronyl transferase and struggles to keep up with the amount of free bilirubin being produced so the levels of free bilirubin in increase

Obstruction of bile:

• obstruction of the flow of bile from the liver and into the small intestine reduces the excretion of conjugate bilirubin
• obstruction of bile Flow generally results in increased conjugated bilirubin in the blood. Blockage of bile duct is most common cause

Question 11

Describe the biosynthesis of bile pigments

Answer 11

Hemoglobin enters the reticulo-endothelial system into kupffer cells were it is split into a heme group and iron group and a biliverdin group is given off. The biliverdin gets changed into bilirubin➡ enters blood stream➡ carried by albumin➡ enters hepatocyte as bilirubin➡ UDPglucuronic acid➡ turns bilirubin into bilirubin diglucuronic acid➡ excreted into intestines➡ further metabolised in large intestine

Question 12

Describe the metabolism of bile pigments in the large intestine

Answer 12

Bilirubin diglucuronic acid➡ deconjuguated➡ bilirubin➡ urobilinogen➡ split one way or other
Reabsorbed then urine
Leave through faeces