Fat digestion

[pm1]

Brain fart..

In regards to fat digestion, triglycerides are broken down to fatty acids by action of lipase assisted by bile. Then due to the fact that FAs are lipid soluble it can go through the cell membrane of the interstitial cells.

Do they have to be transported by Miscelles?

When do they become chylomicrons? And why?

Is there any reason why you want your fat to go through lacteals - lymphatic system - before being dumped into circulatory system?

And, at last, why does the thoracic duct dumps it into veins and not arteries?

I remember there were reasons for all this.. but I can't quite make ordered reasoning..
If someone could clarify these concepts for me it would be GREATLY appreciated.

Thank you!!

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[oOKawaiiOo]

I asked my body this question every day.......

 

[Trayshawn]

I'll try my best.

I dont belive they are transported across the membrane as micelles if thats what you're asking. I think each fatty acid can get through by passive diffusion.

Once inside the enterocyte, the fatty acids are recombined into triacylglycerides and then combine with proteins and other fats (like cholesterol) to make chylomicrons.

The chylomicrons are necessary to transfer the lipids through the aqueous blood. Fats do not dissolve in blood, and thus would not be able to traverse the vascular system on their own. Rather, hydrophylic proteins enclose them within chylomicrons and help the lipids get to wherever they need to go.

The lacteal thing is tougher. The way I rationalized it was that the chylomicrons were simply too big to enter into the very thin capillaries straight from the small intestinal cells. So, rather, they enter the larger lacteals. From there they reach the thoracic duct where, I suppose after a bit of shrinking, they can fit into the normal blood vessels.

Lastly, I dont know if there is a particular reason why the thoracic duct dumps into veins instead of arteries. It is probably just because thats how the organ is designed.

 

[pm1]

I'll try my best.

I dont belive they are transported across the membrane as micelles if thats what you're asking. I think each fatty acid can get through by passive diffusion.

Once inside the enterocyte, the fatty acids are recombined into triacylglycerides and then combine with proteins and other fats (like cholesterol) to make chylomicrons.

The chylomicrons are necessary to transfer the lipids through the aqueous blood. Fats do not dissolve in blood, and thus would not be able to traverse the vascular system on their own. Rather, hydrophylic proteins enclose them within chylomicrons and help the lipids get to wherever they need to go.

The lacteal thing is tougher. The way I rationalized it was that the chylomicrons were simply too big to enter into the very thin capillaries straight from the small intestinal cells. So, rather, they enter the larger lacteals. From there they reach the thoracic duct where, I suppose after a bit of shrinking, they can fit into the normal blood vessels.

Lastly, I dont know if there is a particular reason why the thoracic duct dumps into veins instead of arteries. It is probably just because thats how the organ is designed.

Thank you!!!

yea, in regards to the micelles I read that it just keeps breaking and reforming itself because it doesn't go through the enterocyte once it is hydrophilic. Only FAs go through it.

thank you very much!

 

[mehc012]

I'll try my best.

I dont belive they are transported across the membrane as micelles if thats what you're asking. I think each fatty acid can get through by passive diffusion.

Once inside the enterocyte, the fatty acids are recombined into triacylglycerides and then combine with proteins and other fats (like cholesterol) to make chylomicrons.

The chylomicrons are necessary to transfer the lipids through the aqueous blood. Fats do not dissolve in blood, and thus would not be able to traverse the vascular system on their own. Rather, hydrophylic proteins enclose them within chylomicrons and help the lipids get to wherever they need to go.

The lacteal thing is tougher. The way I rationalized it was that the chylomicrons were simply too big to enter into the very thin capillaries straight from the small intestinal cells. So, rather, they enter the larger lacteals. From there they reach the thoracic duct where, I suppose after a bit of shrinking, they can fit into the normal blood vessels.

Lastly, I dont know if there is a particular reason why the thoracic duct dumps into veins instead of arteries. It is probably just because thats how the organ is designed.

I'll see if I can expound, not because this is incomplete or inaccurate, but to test my own knowledge and also because I always find it helpful to hear things 2 ways in case 1 doesn't work for me.

The fats in chyme glob up into large, hydrophobic bubbles which are difficult for enzymes to penetrate. Bile salts aid in digestion by surrounding these fats and breaking up the BIG fatty globs into much smaller micelles. Fats can then be acted on by enzymes as they shift between the smaller globes.

The fatty acids resulting from this digestion are taken up by the intestinal villi. Once inside the cells, they are reorganized into triglycerides and packaged into chylomicrons along with any other lipids or nonpolar substances. These chylomicrons are dumped into the lacteals because they are too large to diffuse into the capillaries.

The thoracic duct empties into a vein because entering BEFORE the heart enables the contents to be immediately distributed throughout the body, rather than preferentially migrating to the tissues supplied by a single artery. Also, opening a low-pressure system like the lymphatics into a high-pressure major artery would compromise both systems...it would be a weakness in the arterial wall and there would be a lot of back-pressure on the valves in the lymphatic system (and therefore the flow would be compromised, as pressure/valves are the only real impetus for circulation there). Much better to connect to a similarly-low-pressured vein.