1. Lipids: Not Just Fat
BIOL 103, Chapter 6-2

2. Today’s Topics Lipids Digestion and Absorption Lipids in the Body
Lipids in the Diet
Lipids and Health

3. 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

4. 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)

5. 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.

6. 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.
Bloodstream is a water-based environment
Cholesterol esters = cholesterol + FA attached via ester bond (O=CO-)

7. Lipid Digestion and Absorption (Figure 6.21)
I am not covering digestion and absorption of cholestrol

8. 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

9. Lipids in the Body Very-low-density lipoproteins (VLDL):
Deliver triglycerides to cells
Intermediate-density lipoproteins (IDL)
Returns to liver and is converted to LDL
Low-density lipoproteins (LDL)
Deliver cholesterol to cells, which body uses to synthesize membranes, hormones, etc.
Returns to liver afterwards
High-density lipoproteins (HDL)
Pick up cholesterol for removal or recycling

10. 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

11. 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

12. 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
Lip