Digestion & Absorption Of Lipids + Bile

Question 1

Exocrine pancreatic insufficiency

Answer 1

1. Normal function of liver and pancreas can be impaired due to chronic alcohol usage
2. Intolerance to fatty meals causes increase in fat content in stools. Produces pale, malodorous, bulky stools (steatorrhoea)
3. Can occur due to bile salt deficiency or pancreatic insufficiency
4. Bile salts are synthesized in the liver from cholesterol
5. Lipids are water insoluble molecules, so there are special processes (emulsification and formation of micelles) which facilitate digestion and absorption of lipids
6. Emulsification breaks larger fat globules into small droplets and ↑ SA with which lipase can act on
7. Bile salts form small complexes with cholesterol, monoacylglycerol and phospholipids to form micelles
8. Micelle formation facilitates the transportation of products of lipid digestion and makes absorption of lipids easier
9. } Deficiency of bile salts due to diseased liver can cause impaired fat digestion and absorption, leading to intolerance to fatty meals and steatorrhoea
10. Most important enzyme in lipid digestion is pancreatic lipase, which is a component of pancreatic secretion
11. Colipase which is also secreted by the pancreas is the co-activator of pancreatic lipase
12. } Chronic alcohol usage can cause damage to the pancreas, so secretion of pancreatic juice is ↓ leading to deficiency of pancreatic lipase

Question 2

State whether serum lipase estimation is a suitable investigation to assess pancreatitis

Answer 2

1. Lipase is an enzyme secreted by exocrine pancreas and is involved in lipid digestion
2. About 90% of lipase secreted by the GIT is secreted by the pancreas
3. In Pancreatitis, the pancreas becomes inflamed, reducing lipase secretion into the gut and leads to accumulation in the pancreas
4. Leads to lipase leaking into the bloodstream, causing serum lipase to increase
5. Because 90% is secreted by pancreas, elevated lipase level largely indicates defect in the pancreas than any other GIT organ
6. Has a prolonged elevation in blood in comparison to amylase + higher sensitivity
7. Has an acute elevation that can be detected before symptoms are shown
8. Technically simple and less time consuming
9. Used to assess response to medication and progression of the disease
10. Disadvantage: cannot come to a diagnosis with serum lipase essay alone + unsuitable to assess disease severity/outcome

Question 3

Name the end products of digestion of major dietary lipids

Answer 3

1. Short, medium and long chain fatty acids
2. Glycerol
3. 2- monoacylglycerol
4. 1- monoacylglycerol

Question 4

Explain the role of bile in the digestion and absorption of dietary lipids

Answer 4

1. Is produced by the liver (contains 80% water and 10% bile salts)
2. Bile acids are extremely important in fat digestion and absorption
3. Bile salts are produced by using cholesterol as a precursor
4. They are amphiphatic molecules with the presence of both hydrophobic and hydrophilic components
5. 2 main functions in dietary fat metabolism:
   → emulsification of fat
   → absorption of certain fat digestion products
6. Bile salts have a detergent quality used to reduce surface tension
7. Surrounds large fat globules with the peristaltic movements of the intestine and breaks them into small lipid droplets (emulsification)
8. ↑ SA for which lipolytic enzymes may act on + increases efficiency of fat digestion
9. Bile salts bind to lipid digestion products, such as glycerol, fatty acids, cholesterol and other lipids to form complexes called micelles
10. Dietary end products may only be absorbed in soluble form
11. Bile salts contain electrical charges, so renders the complexes semi soluble in chyme and carries them to intestinal mucosa for efficient absorption

Question 5

Explain the derangements in fat digestion and absorption that are likely to occur in immune mediated mucosal destruction of the terminal ileum (Crohn’s disease)

Answer 5

1. Bile salt depletion:
   → Bile salts are critical for emulsifying dietary fats in the SI (breaking them down into smaller droplets so that pancreatic lipases can act upon them)
   → ↓ Bile salt availability for fat emulsification so compromises fat digestion
2. Pancreatic enzyme dysfunction:
   → Pancreas secretes lipases and other digestive enzymes into the SI to breakdown fats into absorbable components
   → Can disrupt the release and activation of pancreatic enzymes
   → Leads to inadequate fat digestion, resulting in increased fat content in the stool (steatorrhoea)
3. Disruption of micelle formation:
   → Bile salts and digested fats form micelles in the intestinal lumen which facilitate the absorption of lipids
   → Can disrupt micelle formation due to bile salt depletion so impairs fat digestion
   → Without micelles, the absorption of fatty acids and fat soluble vitamins (K,A,D,E ) is compromised
4. Malabsorption of fat soluble vitamins:
   → Vit. K,A,D,E requires bile salts and intact micelle formation for efficient absorption
   → Absorption of these vitamins↓ due to impaired micelle formation and disrupted bile salt availability
   → Leads to deficiencies of these vitamins, affecting various physiological processes and leading to clinical manifestations
5. Altered gut microbiota:
   → Terminal ileum plays a role in maintaining gut microbial balance and function
   → Can disrupt the normal gut microbiota composition and function, which in turn can impact fat digestion and absorption
   → May also affect bile salt metabolism and further exacerbate fat malabsorption