digestion/absorption of fats

[km1865]

I was confused about some concepts about fat absorption:

So after the pancreatic lipases act on the the micelles to break them down into fatty acids and glycerol, the fatty acid and glycerols enter the epithelial cells of the small intestine lining (enterocytes?), right? ok so once they are inside the small intesine cells (not in the lumen anymore) the triacylglyerides combine with apoproteins like albumin to form chylomicrons.. so from here on im confused about how the chylomicrons actually end up in the bloodstream, and once they are in teh bloodstream where do they go, and how are they stored/metabolized? I read somewhere that the chylomicrons are directly absobred in the blood stream, but I thought they had to go through the lacteals first to the thoracic duct?

Can anyone clarify this, thanks!

And also, does anyone know if the process of the fatty acids/glycerol entering the enterocytes involves active or passive diffusion? And once the chylomicrons are transported out of the enterocytes either directly to the blood stream (if that is even possible) or into lacteals, does that involve diffusion?

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[Hotshy]

I was confused about some concepts about fat absorption:

So after the pancreatic lipases act on the the micelles to break them down into fatty acids and glycerol, the fatty acid and glycerols enter the epithelial cells of the small intestine lining (enterocytes?), right? ok so once they are inside the small intesine cells (not in the lumen anymore) the triacylglyerides combine with apoproteins like albumin to form chylomicrons.. so from here on im confused about how the chylomicrons actually end up in the bloodstream, and once they are in teh bloodstream where do they go, and how are they stored/metabolized? I read somewhere that the chylomicrons are directly absobred in the blood stream, but I thought they had to go through the lacteals first to the thoracic duct?

Can anyone clarify this, thanks!



And also, does anyone know if the process of the fatty acids/glycerol entering the enterocytes involves active or passive diffusion? And once the chylomicrons are transported out of the enterocytes either directly to the blood stream (if that is even possible) or into lacteals, does that involve diffusion?[/QUOT

Fats are broken down to glycerol and Fatty acids in the lumen. They enter the enterocyte and are put back together into a triglyceride in the smooth ER. They travel through the lacteal and are bound by a chylomicron and move through the lymph and into the blood stream through the thoracic duct. Think about lymph is aqueous (polar) solution so the nonpolar fatty acids need a carrier just like in blood.

 

[Diving Dog]

Yes, and the TAGS don't get all the way broken down into glycerol and fatty acids in the lumen of the intestine...the two outer fatty acids are liberated by pancreatic lipase, but it cannot cleave off the center fatty acid. Thus, the two fatty acids and a monoacyl-glyerol enters the intestinal cell to be repackaged into a TAG. Also the apoproteins don't include albumen...this is a free serum protein that chaperones free fatty acids from adipose tissue to other tissues in the body to use during beta oxidation.