Topic 57 - Catabolism and absorption of lipids

Question 1

Words to include in general about lipids

Answer 1

• Lumen
• Triglycerides
• Sterine
• Sterine-ester
• Phospholipids
• Emulsification
  
  • Bile acids
  • Lecithin
  • Cholesterol
• Fstty acids
• 2-monoglycerides
• Micelle
• Bile salts
• Brush border
• Enterocyte
• Smooth endoplasmic reticulum
• Re-esterified

Question 2

Words to include in lipid catabolism

Answer 2

• Stomach
• Small intestine
  
  • Lipid emulsification
  • Bile acids
  • Lecithin
  • Cholesterol-ester
  • Lipase digestion
  • Triglycerides
  • Phospholipids
    
    • Phosphatidylcholine
    • Lecithin
  • Cholesterol ester
  • Foodstuff
  • Bile
  • Epithelial cells of the intestinal mucosa
  • Bile salts
    
    • Stable emulsification
    • Amphipathic
• Large intestine
• Pancreatic lipase
  
  • Ester bonds
  • Triglycerides
  • 2 Fatty acids
  • 2-monoglycerides
• Phospholipase A2
  
  • Ca²⁺
  • Co-lipase
• Cholesterol esterase
  
  • Cholesterol-ester
  • Triglycerides
  • Ester bonds
• Bile salts

Question 3

Words to include in micelle formation

Answer 3

• Micelle
• Lipid catabolism
  
  • Bile salts
  • Cholesterl
  • Phospholipids
• Spherical components
  
  • Hydrophilic
  • Hydrophobic

Question 4

Words to include in absorption of lipids

Answer 4

• End of jejunum
• Free fatty acids
• Microclimate
• Charge
• Neutral
• Phospholipid bilayer
• Cytoplasm
• Bile salts
• Micelle
• Reabsorbed
• Lipoprotein metabolism
  
  • Cholesterol
  • Triglycerides
  • Absorbed
  • Lipoprotein
  • Chylomicron

Question 5

Topics to include in the essay

Answer 5

1. General about lipids
2. Lipid catabolism
   
   • Stomach
   • Small intestine
   • Large intestine
   • Pancreatic lipase
   • Phospholipase A2
   • Cholesterol esterase
   • Bile salts
3. Micelle formation
4. Absorption of lipids
5. Lipoprotein metabolism

Question 6

Location of lipid digestion

Answer 6

Occurs only in the lumen

Question 7

Give the lipids found in food

Answer 7

• Triglycerides
• Sterine
• Sterine-ester
• Phospholipids

Question 8

Emulsification

Answer 8

• Increases SA
• Enabled by:
  
  • Bile acids
  • Lecithin
  • Cholesterol

Question 9

What does fat digestion results in?

Answer 9

• 2 fatty acids
• 2-monoglycerides
  
  • Forms micelles with bile salts → digested product get to the brush border → go trough the fat-soluble membrane → enters enterocyte → smooth endoplasmic reticulum (SER)
• Fatty acids in SER are re-esterified

Question 10

Lipid catabolism

Lipid catabolism in the stomach

Answer 10

Lipids are emptied from the stomach later than the rest of the gastric content (due to oily phase)

Question 11

Lipid catabolism

Lipid catabolism in the small intestines

Answer 11

• Lipid emulsification occurs in the small intestines due to:
  
  • Bile acids
  • Lecithin
  • Cholesterol-ester
• Lipase digestion occurs at the border of the water-lipid phase
• Fats in the intestines contains:
  
  • Triglycerides
  • Phospholipids
  • Cholesterol ester
• These substances enter the intestinal canal with:
  
  • Foodstuff
  • Excreted by bile
• Bile salts are able to keep the digested fat components in a stable emulsion
  
  • Bile salts are amphipatic

Question 12

Lipid catabolism

Lipid catabolism in the large intestines

Answer 12

• Lipid content of duodenum inhibits gastric motility
  
  • Helps digestion and emulsification

Question 13

Lipid catabolism

Which substances takes part in lipid catabolism

Answer 13

• Pancreatic lipase
• Phospholipase A2
• Cholesterol esterase
• Bile salts

Question 14

Lipid catabolism

Pancreatic lipase

Answer 14

• Water-soluble molecule which can digest lipids at the lipid-water interphase
• Cleaves ester bonds in 1^st and 3^rd position of the triglycerides, and results in:
  
  • 2 fatty acids
  • 2-monoglycerides

Question 15

Lipid catabolism

Phospholipase A2

Answer 15

• Cleaves phospholipids in presence of:
  
  • Ca²⁺
  • Co-lipase

Question 16

Lipid catabolism

Cholesterol esterase

Answer 16

• Hydrolyses:
  
  • Cholesterol-ester
  • 2^nd bond of triglycerides
  • Ester bonds of other lipids

Question 17

Lipid catabolism

Bile salts

Answer 17

Stabilize digested lipid emulsion

Question 18

Micelle formation

Answer 18

• Micelles are formed in a combination from:
  
  • Substances produced from lipid catabolism
  • Bile salts
  • Cholesterol
  • Phospholipids
• Spherical components:
  
  • Hydrophilic part
  • Hydrophobic part
  • Apolar (lipophil) molecules found inside micelle

Question 19

Absorption of lipids

Answer 19

• Terminates in the end of jejunum
• Free fatty acids protonated at superficial microclimate → charge disappears
• Neutral molecules diffuse through phospholipid bilayer and absorbed into cell cytoplasm
• Bile salts at border phase of micelle reabsorbed by specific transport

Question 20

Lipoprotein metabolism

Answer 20

When cholesterol and triglycerides are absorbed in the intestines, they form the largest lipoprotein, chylomicron

Question 21

Chylomicrons

Answer 21

• Resynthesized lipids and cholesterol appear in the cell and form chylomicrons, in which apolipoproteins are embedded
  
  • Makes it possible for blood to transport hydrophobic substances
  • Capillaries can regulate lipid uptake from chylomicrons via their specific receptors
• On the surface of chylomicrons:
  
  • C-type apolipoprotein
    
    • ​Activator of the lipoprotein lipase present in the capillary wall, through which it binds to the endothelial receptor of the capillary and facilitates its activity
  • B-48-type apolipoprotein
    
    • ​Takes part in the structure and secretion of the chylomicrons
  • E-type apolipoprotein
    
    • ​Takes part in the binding of chylomicron remains (remnant) to liver-like receptors
• Chylomicrons are transformed due to the effect of lipoprotein lipase (LPL) in the capillaries: FFA are released, which are transported by albumin to the target organs (muscle, liver, adipose tissue)
• Chylomicrons in capillaries are bound with the help of the C-type apolipoprotein
  
  • ​Disappear from the surface of the chylomicrons after destruction

Figure: lipoprotein metabolism