PHIS 206 Lecture Notes - Lecture 27: Bile Acid, Micelle, Lecithin
2 May 2018
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Lecture 27: More Absorption, Large Intestine, Hormones
Fats
• Overall Goal
o Convert triglycerides from diet into free fatty acids and monoglycerides
The Issue With Fat
• The enzymes that digest fat are H2O-soluble and the general environment of the gut
lumen is an aqueous (watery) one.
• Without intervention, dietary fats would float on top of the watery gut contents,
separating them from the enzymes that digest them, and making their movement through
the gut difficult to regulate.
• An emulsion of fat and gut contents does occur in the stomach, but it’s not stable. More
help is needed to keep the fats where we want them.
Micelle Formation
• Micelles
o One arrangement of bile salts and ingested nutrients is the micelle, which allows
for an interior ”pocket” where enzymes can work upon the ingested lipid
products.
o Lecithin aids the bile salts in micelle formation.
o Micelle is quite stable in an aqueous environment
Fat Digestion and Absorption I
• Emulsion Stage
o Enzymes from the oral cavity and pancreas breakdown complex fats
(triglycerides) into simpler monoglycerides and free fatty acids.
o The emulsion created in the stomach (and stabilized by bile from the liver) allows
this.
Fat Digestion and Absorption II
• Micelles
o The monoglycerides and free fatty acids become contained in micelles (with help
of bile salt and lecithin).
o The micelles drift to the edge of the lumen, and their contents diffuse without
assistance into the cells that line the intestine.
o PASSIVE
Fat Digestion and Absorption III
• The Chylomicron
o Once inside the cells, these simple fats are repackaged into a more complex
structure, the chylomicron.
o These chylomicrons are released via exocytosis into the lacteals (lymphatic
vessels) for absorption (not into the veins that drain the gut)
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