Digestion And Absorption Of Lipids(Week 2) Flashcards
Give an overview of lipid digestion and explain why lipids may be more difficult to digest.
Lipids are hydrophobic molecules and need to be solubilised to ensure adequate mixing. The digestion starts in the mouth and moves to the stomach but most of the work occurs in the small intestine. Bile salts produced from cholesterol in the liver and secreted by the gallbladder surround and emulsify lipids so the pancreatic lipases can interact with the lipids
What role does the liver have in lipid digestion?
Bile acids are synthesised from cholesterol in the liver.
How do bile salts work to digest lipids?
They act as detergents assisting the emulsification of ingested dietary lipids into very small globules.
How are gall stones formed?
When there is excess cholesterol which crystallises
Which enzyme digests triacylglycerols into fatty acids and monogylcerides?
Triacylglycerol lipase
Which enzyme breaks down phospholipids into fatty acids and lysolecithin?
Phospholipids A2
Give an overview of how lipids are transported.
Long chain fatty acids (above 12 carbons) concentrate into micelles in the lumen of the small intestine. Close to the surface of the apical membrane the micelles disperse, and these long chain fatty acids diffuse across the apical membrane. In the cytoplasm, long chain fatty acids are attached to monoacylglycerol to form triacylglycerol. These are packages with cholesterol to form chylomicrons. These are exocytosedthrough the base lateral membrane into the interstitial space where they enter the bloodstream via the lymphatic system.
Describe the structure of a lipoprotein
Lipoproteins have a central core of cholesterol esters and triacylglycerols surrounded by a single layer of phospholipid, free cholesterol and proteins.
Give three uses of cholesterol
Bile acids
Steroid hormones
Vitamin D
How do humans get cholesterol?
It is obtained in the diet through meat,eggs and dairy products.
It can also be synthesised, mainly in the liver.
What are the dangers of cholesterol levels getting too high?
Fatty deposits in the arteries which lead to reduced blood flow, increased blood pressure and atherosclerosis
What is the most effective way of reducing cholesterol levels?
Statins
How do statins work?
Inhibiting HMG-CoA reductase (an enzyme in the biosynthetic pathway of cholesterol)
What is the role of chylomicrons?
Move dietary triacylglycerols from the intestines to the peripheral tissues
Which type of lipoprotein is the ‘bad’ kind and which is the ‘good’ kind of cholesterol?
Low density lipoproteins are known as the bad kind of cholesterol as they can deposit in the arteries and form plaques.
High density lipoproteins, by contrast return excess cholesterol to the liver where it can be converted to bile and excreted
