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Lipid Absorption

Right so I am a little confused because the way I have been taught about lipid diffusion is as follows:

Bile emulsifies lipids into micelles

Lipase acts on Micelles to form predominantly fatty acids and monoglycerides

These all diffuse into cells via simple diffusion

These reform in the SER

Go to the Golgi and for with a protein and cholesterol to form chylomicron

Enter lacteal


But in my A Level book and on certain websites it says that the Miscelles diffuse into the epithelial cells first and then lipase acts on it. Which way round is it?

Thanks
(edited 2 years ago)
@chris01928

Hi,

Most digestion [of all types of food] takes place in the lumen of the alimentary tract - emulsification does involve formation of micelles, yes, but the best way to look at this process, which is aided by bile secreted by the liver] is that the lipid mixes with water and because neither is soluble in the other, the fat breaks up into numerous minute globules [micelles] that are spread out "and mix" with the water.

The whole point of digestion, be it fats or other foods [proteins + carbs mainly] is to make the molecules smaller so that they can be absorbed into the [here] intestines - large molecules like whole fats, proteins and complex carbs [polysaccharides] are too large to be absorbed.

Therefore, the answer to your Q is that digestion into fatty acids and monoglycerides [as you correctly say] OCCURS IN THE LUMEN OF THE INTESTINE SO THAT THE PRODUCTS CAN BE ABSORBED through the cell membrane of the endothelial cuboidal/columnar cells lining the villi.

In addition, the main enzyme that catalyses this decomposition [chemically] is pancreatic lipase, which is secreted via the pancreatic duct and sphincter of Oddi into the duodenum - it is virtually absent from the endothelial cell cytoplasm, although oc some enzyme will be needed to reconstitute the lipids later, as again, you correctly say [remember: enzymes can drive a reaction in either direction, depending on temp, pH, etc].

Be safe!
M.

Sorry but your book is incorrect!
(edited 2 years ago)
Original post by macpatgh-Sheldon
@chris01928

Hi,

Most digestion [of all types of food] takes place in the lumen of the alimentary tract - emulsification does involve formation of micelles, yes, but the best way to look at this process, which is aided by bile secreted by the liver] is that the lipid mixes with water and because neither is soluble in the other, the fat breaks up into numerous minute globules [micelles] that are spread out "and mix" with the water.

The whole point of digestion, be it fats or other foods [proteins + carbs mainly] is to make the molecules smaller so that they can be absorbed into the [here] intestines - large molecules like whole fats, proteins and complex carbs [polysaccharides] are too large to be absorbed.

Therefore, the answer to your Q is that digestion into fatty acids and monoglycerides [as you correctly say] OCCURS IN THE LUMEN OF THE INTESTINE SO THAT THE PRODUCTS CAN BE ABSORBED through the cell membrane of the endothelial cuboidal/columnar cells lining the villi.

In addition, the main enzyme that catalyses this decomposition [chemically] is pancreatic lipase, which is secreted via the pancreatic duct and sphincter of Oddi into the duodenum - it is virtually absent from the endothelial cell cytoplasm, although oc some enzyme will be needed to reconstitute the lipids later, as again, you correctly say [remember: enzymes can drive a reaction in either direction, depending on temp, pH, etc].

Be safe!
M.

Sorry but your book is incorrect!

Oh, my book did get it right! Maybe I worded it poorly but I said that monoglycerides and fatty acids are made (didn't say in the lumen but that is what I want) and then diffuse into the epithelial cells. - this is what you said right?

The stuff about the sphincter of Oddi is something I have no idea about:lol: far too high brow for me.

Thank you for taking the time to write this:smile:
Original post by chris01928
Oh, my book did get it right! Maybe I worded it poorly but I said that monoglycerides and fatty acids are made (didn't say in the lumen but that is what I want) and then diffuse into the epithelial cells. - this is what you said right?

The stuff about the sphincter of Oddi is something I have no idea about:lol: far too high brow for me.

Thank you for taking the time to write this:smile:

P-graph 1: Yes correct.

P " 2: dw you don't need this for A level [tho knowing it might help you get superb marks in synoptic Q]

P " 3: No probs!

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