152b - Bile Salts and Absorption of Lipids

Question 1

Bile acid and cholesterol metabolism are ~intimately~ linked

How?

Answer 1

• We need bile to absorb cholesterol
• We need cholesterol to make bile

Question 2

List the 4 components of bile

Answer 2

• Bilirubin
• Phospholipids
• Cholesterol
• Bile acids/salts

Question 3

Which macronutrient would be most affected by ileal resection?

Answer 3

Fats

• Fat absorption relies on bile
• Bile acids are re-uptaken in the ileum
• Also, decreased absorptive surface area

Question 4

Pancreatic lipase converts triglycerides into:

Answer 4

2-monoacylglyceral + 2 free fatty acids

Question 5

What is the difference between a bile acid and a bile salt?

Answer 5

Bile acids are conjugated to taurine or lysine to form bile salts

Question 6

Where in the GI tract are most bile acids re-uptaken?

Answer 6

Ileum

Question 7

Which enzyme catalyzes the rate limiting step in bile acid synthesis?

What regulates this enzyme?

Answer 7

CYP7A1

[Can remember this by knowing 7-alpha-hydroxylase is Rate-limiting step in cholesterol=>unconj. bilirubin synthesis)

• Downregualted when bile acids bind FXR or GFG19 (negative feedback)

Question 8

Describe the absorption of triglycerides

Answer 8

• Pancreatic lipase turns triglycerides into 2-monoacylglycerol + 2 free fatty acids
  
  • Short and medium chain fatty acids are incorporated into mixed micells (thanks, bile!!) and absorbed
• Long chain fatty acids are re-esterified (turned back into a triglyceride)
• New triglyceride is packaged into a chylomicron
• ​Chylomicrons diffuse into the lymphatic system
• Eventually, they get from lymphatics -> bloodstream

Long chain fatty acids do not go directly to the bloodstream

Question 9

Which macronutrient most significantly influences pancreatic enzyme release?

Answer 9

Fat

Question 10

If (for some reason) a patient cannot make bile, which fatty acids would they still absorb?

Answer 10

Long chain fatty acids

Incorporated into chylomicrons and dumped into the lymphatics

Question 11

List 3 causes of gallblader stasis

What is a potential consequence?

Answer 11

• Prolonged fasting
• Total parenteral nutrition
• Pregnancy

Bile becomes more concentrated the longer it stays in the gallbladder

Supersaturation -> precipitation of gallstones