Lipids – Part 2 McCafferty. LIPID DIGESTION & ABSORPTION Absorbable forms:
02 Digestion of Lipids
Transcript of 02 Digestion of Lipids
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Lipid Digestion
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Monogastric Digestion Challenges
Lipids are not water soluble
Triglycerides too large to be absorbed
Digestive solution
Triglycerides mix with bile and pancreatic
secretions Emulsification and digestion
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Bile Produced in liver, stored in gallbladder
Except horse
Alkaline solution composed of: Bile salts Cholesterol Lecithin Bilirubin
Responsible for fat emulsification Detergent action
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Mixed micelle formed by bile salts, triacylglycerols and pancreatic lipase.
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Digestion of Lipid Bile salts emulsify lipids
Pancreatic lipase acts on triglycerides
Triglycerides sn-2 monoglyceride + 2 fattyacids
Pancreatic colipase
Activated by trypsin
Interacts with triglyceride and pancreatic lipase
Displaces bile to allow recycling
Improves activity of pancreatic lipase
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Pancreatic Colipase Secreted from pancreas as
procolipase
Activated (cleaved) bytrypsin
Anchors lipase to the
micelle One colipase to one lipase
(i.e., 1:1 ratio)
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Dietary Fat
(large TG droplet)
Bile Salts
Lipid emulsion
Lipase 2-Monoglyceride
+ 2 FFA
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Emulsification Produces small lipid spheres
Greater surface area
Lipases attack TG at 1 and 3 positionsGly
cerol
Fatty Acid1
Fatty Acid2
Fatty Acid3
Lipase
Gly
cerol
Fatty Acid3
Fatty Acid1
Fatty Acid2
Triglyceride 2-Monoglyceride
+
2 Free Fatty Acids
2 H20
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Digestion of Lipid Phospholipase A1 and A2
Hydrolyzes fatty acids from phospholipids
Cholesterol esterase
Hydrolyzes fatty acids from cholesterolesters
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Micelle Formation Complex of lipid materials soluble in
water
Contains bile salts, phospholipids &cholesterol
Combines with 2-monoglycerides, free
fatty acids and fat-soluble vitamins toform mixed micelles
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Micelle Formation
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Nutrient Absorption - Lipids Fatty acids, 2-monoglycerides,
cholesterol, and cholesterol esters move
down concentration gradient (passivediffusion)
Repackaged in intestinal cell fortransport to liver Some is reformed into triglycerides
Chylomicrons
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In the Enterocyte... Newly formed triglycerides accumulate
as lipid droplets at the endoplasmic
reticulum Coated with a protein layer
Stabilizes lipids for transport in lymph and blood(aqueous environment)
Glycerol and short chain fatty acids directlyenter mesenteric blood
These protein-coated lipid droplets are called chylomicrons
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Lipid Absorption
Short andmedium
chain fattyacids
simple diffusion exocytosis
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Lipid Absorption (Chylomicrons)
Chylomicrons absorbed fromenterocytes into lacteals (lymph
vessels) Ultimately enter blood via thoracic duct
Most long chain fatty acids absorbed into
lymphatic system Exception is poultry
Blood lipids transported as lipoproteins
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Overview of Fatty Acid Uptake Short- and medium-chain fatty acids
Enter portal blood directly from enterocytes
Bound to albumin in blood AlbuminFFA complex
Oxidized in liver or elongated and used fortriglyceride formation
Long-chain fatty acids Form chylomicrons Drain into the lymphatics via the lacteal in
mammals (no lacteal in avian small intestinal villi)
Enter bloodstream at the thoracic duct
Upstream from liver Slow entry into the blood
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Overview ofLipid
Digestion inMammals
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Overview of Lipid Digestionand Absorption in Avians
Portal
blood
*
*Lymph in mammals
Fatty
acid
binding
protein
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Lipid Digestion - Ruminants
Microbes rapidly modify lipids:
Lipolysis
Triglycerides Glycerol + 3 free fatty acids
Biohydrogenation
Addition of H to unsaturated fatty acids
Saturation
If carried to completion, all double bonds becomesingle bonds
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Biohydrogenation
Weight percent of fattyacids
Fatty acid Diet Abomasaldigesta
16:0 (palmitic)
18:0 (stearic)18:2 (linoleic)
18:3 (linolenic)
26
617
31
29
454
6
Sheep fed alfalfa hay
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Biohydrogenation
Reduction of double bonds
Result: fatty acids that are more
saturated with hydrogen
Saturated
Unsaturated
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Biohydrogenation of Linoleic Acid
Linoleic acid (18:2)
cis-9, trans-11 CLA
trans-11 18:1
Stearic acid (18:0)
isomerase
reductase
reductase
Intermediate fat ty acids are conjug ated l in oleic acids
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Lipid Digestion and Synthesisby Microbes
Rumen microbes
Produce trans configured double bonds
Alter chain length Change position of double bonds
Produce odd-chain and branched-chain FA
Rumen adipose tissue varies greatly from
dietary fat Dietary fat must be rumen protected to affect
animal
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Effect of Lipid on RumenFermentation
Excess amounts of unsaturated fatty acidsand triglycerides Decrease methane production Impair fiber digestion Form soaps Alter rumen metabolism towards propionate
production less acetate Decrease milk fat
Produce trans fatty acids Inhibit lipid synthesis in mammary gland
Decrease milk fat
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Lipid Digestion - Ruminant
Digestion and absorption of lipids issimilar to monogastrics except
Fat enters small intestine in different formthan was presented to animal in diet
Lipids absorbed more slowly