Lipids Hydrophobic vs. hydrophilic –For something to be soluble in water (and therefore hydrophilic) it must have a charge –Triglycerides don’t have any.

Lipids• Hydrophobic vs. hydrophilic

– For something to be soluble in water (and therefore hydrophilic) it must have a charge

– Triglycerides don’t have any charges (hence the name neutral lipids)

– Phospholipids have charge from the phosphate group so they have a hydrophilic end and a hydrophobic end

Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning

Phospholipids


Phospholipids


Hydrophilic (Charged) “Head”Including Glycerol part and charge from Phosphate and Nitrogen

Hydrophobic “Tails”

Phospholipids


Phospholipids• Phospholipids in foods

– Lecithin – Found in eggs, liver,

soybean, wheat germ and peanuts

• Roles of phospholipids– Plasma membrane– Emulsifiers


Membrane fluidity

Cholesterol(only in animal cells)

http://telstar.ote.cmu.edu/Hughes/tutorial/cellmembranes/

http://telstar.ote.cmu.edu/Hughes/tutorial/cellmembranes/

Sterols

Copyright 2005 Wadsworth Group, a division of Thomson Learning

Copyright 2005 Wadsworth Group, a division of Thomson Learning

Sterols• Sterols in foods

– Plant sterols• May help to reduce cholesterol when

eaten• Small quantities are present in many

plant products• Long term effects of taking extra plant

sterols are not known• http://www.ific.org/publications/factsheets/sterolfs.c

fm

– Animal Sterols• Cholesterol only comes from animals


http://www.ific.org/publications/factsheets/sterolfs.cfm

http://www.ific.org/publications/factsheets/sterolfs.cfm

Sterols• Roles of sterols in the body

– Bile acids– Sex hormones– Adrenal hormones– Vitamin D


Sterols• Cholesterol and atherosclerosis

– Liver makes cholesterol (800 to 1500 mg per day

– More than anybody eats– Atherosclerosis happens when

cholesterol is deposited on the walls of arteries


Fat Digestion• Hydrolysis

– Triglycerides monoglycerides, fatty acids, glycerol


Fat Digestion



Mouth MeltingLingual lipase Important in infants (short chain fatty acids from milk)Minor in adults

StomachChurning and mixingGastric lipase Needs acid condition to workDigests only a little bit of the fat in food

Small intestineCCKBile and emulsificationSmall intestinePancreatic lipasesIntestinal lipases

Large intestineSome fat and cholesterol trapped in fiber and lost

Fat Digestion


Soaps• Soaps clean by acting as emulsifying agents

– their long hydrophobic hydrocarbon chains cluster so as to minimize their contact with water

– their polar hydrophilic carboxylate groups remain in contact with the surrounding water molecules

– driven by these two forces, soap molecules spontaneously cluster into micelles

– http://www.chipola.edu/instruct/science/Breivogel/Powerpoint-bch3023/Chapter%2012%20Lipids.ppt#11

Fat Digestion


Fat Digestion

• Enterohepatic circulation



Lipid Transport• Lipoproteins

– Chylomicrons– VLDL = very-low-density

lipoproteins– LDL = low-density lipoproteins– HDL = high-density lipoproteins


Lipid Transport Animation

Lipid Transport• Lipoproteins and health

– LDL vs. HDL


Why are fats absorbed through the lymphatic system?

• To answer this lets go back to the fat absorption process in the enterocytes– The fats are absorbed in either as fatty acids or

monoglycerides– Then they are remade into triglycerides– (But remember fats started off as triglycerides

to begin with)– So why remake triglycerides?

– High concentrations of free fatty acids near the inner side of the cell membrane can be toxic to the cells

– Sodium-free fatty acids and soaps are used to dissolve oils on your skin

– Imagine what that would do cell membranes!– So inside the enterocytes the fatty acids are ferried

around by fatty acid binding proteins combined to form triglycerides which then coalesce together with cholesterol and proteins and form chylomicrons

• Chylomicrons belong to a group of compounds referred to as lipoproteins.

They all contain a core of lipids and a shell of protein, cholesterol and phospholipids. This outer shell acts as an emulsifier, allowing the lipid it is carrying to be transported in a water-based fluid such as blood or lymph

• The proteins associated with the chylomicrons direct the uptake and breakdown of the chylomicrons in tissues

• Chylomicrons are very large particles (Remember they can be visualized by electron microscopy)

• They average between 100-500 nm in diameter

• Because of their size they are excluded from entering the blood

• The lymph capillary cells also cannot allow chylomicrons is but..

• Lymphatic capillaries function in a slightly different way to bring lymph in.

• http://www.jdaross.mcmail.com/lymphatic_system.htm

http://www.jdaross.mcmail.com/lymphatic_system.htm

http://www.jdaross.mcmail.com/lymphatic_system.htm

Chylomicrons are big and reflect enough light that after a fatty meal you can see them in plasma (blood without the red blood cells). The tube on the left is without chylomicrons and the one on the right has chylomicrons in it. The pinkish material is a collection of chylomicrons.

Picture from: http://arbl.cvmbs.colostate.edu/books/pathphys/digestion/smallgut/absorb_lipids.html

• Besides chylomicrons, however, there are other types of lipoproteins which carry lipids in the blood.

The four major types of lipoproteins are:

• Chylomicrons

• VLDLs (Very Low Density Lipoproteins)

• LDLs (Low Density Lipoproteins)

• HDLs (High Density Lipoproteins)

Roles of Triglycerides• Fat stores

– Energy– Protection– Insulation


Lipids Hydrophobic vs. hydrophilic –For something to be soluble in water (and therefore hydrophilic) it must have a charge –Triglycerides don’t have any.

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