Lipid digestion

Question 1

Describe the composition of large fat drops

Answer 1

made of dietary fat as tracylglycerol (TAG)
TAG = formed by condenssation reaction between glycerol ester and 3 fatty acids

Question 2

How does bile acid reduce fat drop size?

Answer 2

CCK (from stretched duodenum and low pH) stimulates bile acids to be secreted from gall bladder into SI
Bile acids start the emulsion process
Phospholipase A2 (from pancreas) transforms lecithin (in bile) into hysophospholipids which acts as strong detergents
Lingual lipase and pancreatic lipase catalyse the hydrolysis of triaglycerols (catalysed by colipase)

Question 3

What happens to lipids in intestinal epithelium?

Answer 3

Accumulate in endoplasmic reticulum and TAGs molecules are reformed via an intracellular fatty-acid binding protein
Cholesterol transformed into cholesterase
TAGs/lipids/cholesterol/cholesterase gather to form lipoproteins/chylomicrons

Question 4

What is the major protein component of chylomicrons?

Answer 4

apolipoprotein B
forms a hydrophilic shell around lipid layer and allows it to form a stable structure in the blood

Question 5

How do chylomicrons enter the blood?

Answer 5

Too big to enter systemic circulation via capillaries
Exti via exocytosis into lymphatic system
Lymph drains into circulation via thoracic duct to bypass hepatic metabolism

Question 6

How do chylomicrons produce energy?

Answer 6

Apoprotein on surface activates lipoprotein lipase which catalyses hydrolytic cleavage of fatty acids from TAGs of chylomicrons
Released fatty acids and monoacylglycerols are picked up by body cells for use as energy sources

Question 7

Describe the change in chylomicrons as they travel through the ciculation

Answer 7

Become more dense as they travel through and TAGs are taken up by cells
Chylomicron
VLDL - very low density lipoprotein
IDL - intermediate density lipoprotein
LDL - low density lipoprotein
HDL - high density lipoprotein