Date post: | 24-Dec-2015 |
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Today’s Topics
• Lipids Digestion and Absorption• Lipids in the Body• Lipids in the Diet• Lipids and Health
Lipid Digestion
• Digestion of triglycerides (TG), cholesterol, and phospholipids (PL)– Mouth• Chewing + lingual lipase secreted by salivary glands
tiny fat droplets
– Stomach• 30% Triglycerides + gastric lipase FFA and DG
Lipid Digestion (cont.)
• Small Intestine– Emulsified by bile (bile salts and lecithin/PL in the body)– Rest of the “exposed” TG and DG are digested by
pancreatic lipase MG, glycerol and FFA– Phospholipids + pancreatic phospholipase
lysolecthicin/LsL and FFA– Cholesterol ester + cholesterol esterase FFA +
cholesterol– Bile salts surround MG, FFA, cholesterol, and
lysolecthicin forming micelles (tiny emulsified fat packets made up of phospholipids)
Lipid Digestion (cont.)
• Micelles carry MG, LyL, cholesterol, and long-chain FA through the watery environment to microvilli/small intestine– The lipid components are then absorbed into the
intestinal cells at the microvilli– Bile salts return to the liver to be used again
• Short-chain FA and glycerol are directly absorbed into your intestinal cells without the help of micelles.
Lipids Absorption
• To travel in the bloodstream, lipids are packaged into lipoprotein carriers
• How? – In your intestinal cell: MG + FFA rejoin TG
• Cholesterol esters and phospholipids form here also
– Then, TG, PL, cholesterol esters join protein carrier lipoprotein.
– Lipoprotein leaves the intestinal cell chylomicron goes to lymph system bloodstream.
Chylomicron Transport
• In the blood stream, chylomicrons are large, fatty lipoproteins (90% fat) circulate in the body while releasing TG
• When reaching capillaries, lipoprotein lipase “attacks” chylomicrons to remove TG FFA and glycerol:– FFA enter adipose cells reassembled into TG– OR FFA enter muscle cells used for energy– Glycerol liver or kidney
• Your liver picks up “left-over” chylomicron and uses them to build VLDL
Lipids in the Body1. Very-low-density lipoproteins (VLDL):– Deliver triglycerides to cells
2. Intermediate-density lipoproteins (IDL) – Returns to liver and is converted to LDL
3. Low-density lipoproteins (LDL)– Deliver cholesterol to cells, which body uses to
synthesize membranes, hormones, etc.– Returns to liver afterwards
4. High-density lipoproteins (HDL)– Pick up cholesterol for removal or recycling
Lipoprotein density
• Lipoproteins differ by size, density, and composition of their lipid cores– In general, larger the lipoprotein, the less dense it
is.– Size: HDL < LDL < IDL < VLDL < Chylomicron
Lipids in the Diet
• Recommended intake:– Reduce saturated fat and trans fat– Total fat: 20-35% of calories– Less than 10% of calories from saturated fat
Lipids in the Diet
• Essential FA requirements– Linoleic acid/omega-6 FA should provide about 2%
of calories– Requirements for omega-3 FA is less well-known
• Omega-6 and omega-3 FA balance– Ratio of 6:1 (omega-6 to omega-3 FA)– While omega-3 FA is good for you, consuming too
much of the omega-3 FA can suppress immune function and prolong bleeding time