Lipid digestion and absorption
From Iusmphysiology
- started here on 02/23/11 at 11AM
Contents |
[edit] Lipid digestion and absorption
[edit] Formulas of some common lipids
- Lipids are anthrophilic
- In bulk amounts, bilayers and micells are formed.
- Most dietary lipids are TAGs
- Some include vitamins
- Typical western diet includes 100 g of fat which provides 40% of our diet.
- Less than 70 g is healthy, less than 30%
- Most of our diet is TAGs
- Fat is important for postprandial satiety; it tells us we are full.
[edit] Dietary lipids
- 90% from TAGs
- The other 10% of fats:
- Phospholipids from meat (like lesothin) is 5%
- Sphingolipids about 5%
- Cholesterol makes up less than 0.5 grams
- Comes in esterified and unesterified
- Comes from liver and things made with blood products
- Lipovitamins and provitamins
- Skin lipids; difficult to digest
[edit] Endogenous lipids
- Mostly lecithin, cholesterol, from bile
- Also membrane lipids from disquamated intestinal epith.
- Bile:
- Lots of lipids in the bile
- Membrane lipids:
- From shedd epithelial cells
- ?
[edit] Emulsification of dietary fats
- Key / preliminary step is transforming solid fats into emulsified droplets.
- This begins with food prep as the hamberger is pounded out.
- Then chewing helps break it up
- Then gastric churning
- Then instestinal peristalsis mixing
- All these mechanical processes increase the ratio of surface area.
- Generates lipid droplets = micelles
- Emulsion droplets are covered with proteins, polysacchs, fatty acids, monoglicerides, biliary stuff, etc.
- This keeps the lipis from coalescing
[edit] Lingual and gastric lipases
- Lipase is water soluble, hydrolyzes ester bonds in the lipid.
- First lipase is lingual lipase
- From Ebner's grlands on dorsal side of the tongue
- Starts in mouth, most active in stomach.
- Gastric lipase
- From gastric chief cells
- Lipases have four properties:
- Acidic pH optimal activit
- stable at low pH
- resistant to pepsin digestion
- ?
- Lipases release single fatty acid from TAGs
- Carboxy terminal of long chain FAs are hydroxylated and therefore not absorbed.
- Medium and short chains are solubleized at pH 4 so they can be absorbed in the stomach
- 15% of the fat digestion occurs in the stomach in adults
- Much more in infants b/c of high milk fat
- In infants, gastric lipase much more important b/c lingual is expressed yet.
[edit] Pancreatic enzymes
- Fat digestion fisished in proxmial si.
- CCK stimulated in stomach, CCK stimulates release of Bile
- Pancreatic enzymes are released in 1000 fold excess.
- Pancreatic lipase is only active at water-lipid interface
- But emulsifiers inhibit pancreatic lipase
- Colipase reverses this inhibition by helping anchor it to the lipid
- Por-colipase is cleaved by trypsin
- Enterostatin decreases appetite
- Pancreatic lipiase cuts TAGs into monoglyceride and diglyceride with glycerol backbone
[edit] Milke lipase and others
- Missed this slide
[edit] Products of lypolysis
- Several small vesicles come off of micelles
- Multicellular vesicles
- Lipases cut off chunks of the micelles.
- ...
[edit] Micellar transport
- Three phases:
- Bulk phase: lipase works on surface and releases monoglyc and diglyc
- Making mixed micilles
- Acid microclimate dissequilibirum zone phase
- Driven by exchange of Na and hydrogen
- Protons protonate the lipids
- Lipids then diffuse accors via non-ionic diffusion or coallesce with the bilayer to enter the enterocyte
- 3rd:
- Long chain fatty acids put back together as TAGs
- Apoproteins are made in enterocyte, moved to reticulum, associate with lipid droplets.
- Then VLDLs and chylomicrons are made
- These two vesicles get glycosylated in golgi
- Then go to membrane and get exported
- 5 different lipoprotiens:
- Chylomicrons are large
- VLDL are pretty big too, so they go to the lymphatics
- Bulk phase: lipase works on surface and releases monoglyc and diglyc
[edit] Summary
- stopped here on 02/23/11 at 11:45AM.
