Lipids Flashcards
Describe the physical properties of fats
Hydrophobic
Floats in water, dissolves in alcohol
Does not evaporate
Can be solid or liquid at room temperature
Discuss the essential fatty acids and their major roles
Cannot be synthesized in animal cells and must be obtained in diet.
Linoleic acid and alpha-linoleic acid
Deficiency: retarded growth, dermatitis, KD skin lesions, death
–reversed with linoleic, alpha-linoleic and arachidonic acids
Functions: Formation of longer, more highly unsaturated fatty acids -formation of cell membranes -production of eicosanoids ---prostaglandins ---thromboxanes ---leukotrienes
Describe the digestion of dietary lipids
Stomach: 10-30% of fat digestion - minor Lingual and gastric lipases - Activated by acidic environment - Break apart lipids - Act on TGs containing short and medium chain FAs Presence of fats in stomach slows gastric emptying High satiety values
Small intestine:
70-90% of fat digestion - primary site
Cholecystokinin (CCK)
- Hormone produced by epithelial cells of SI
- Stimulate release of:
– Bile, from gallbladder, emulsifiers fats creating micelles
– Bicarbonate and pancreatic lipases, from pancreas, break down fats into monoglycerides and free FAs
Describe the absorption of dietary lipids
Micelles:
Formed by a combination of monoglycerides and FAs with bile salts
Interact with brush border
Monoglycerides and FAs diffuse into enterocytes
Short and medium chain FAs:
Enter the portal blood
Bind to albumin
Transported to liver
Long chain FAs:
Reform into TGs in intestinal cells
Converted into chylomicrons
Enter the lymphatic system
Describe the transport of dietary lipids
Chylomicrons:
Enter blood stream via lymphatic thoracic duct
Deliver dietary lipids to tissues other than liver
- Mainly muscle and adipose
- Cells that need them can use the TGs from chylomicrons by breaking it down with lipoprotein lipases found in the blood vessels
Chylomicron remnants are delivered to liver
VLDL:
Transport TGs from liver to circulation
Cells that need it can use the TGs in VLDL by breaking it down with lipoprotein lipases
Left over protein and cholesterol shell is called LDL
LDL:
Delivers cholesterol to cells for
- plasma membrane construction
- conversion into other metabolites i.e. hormones, steroids, vit D
Taken up by LDL receptors on cell membranes
Evaded levels of LDL can cause fatty plaque formation and increase risk of blood clots
Explain the importance of cholesterol
Essential component of cell membranes Precursor of other important steroids - bile acids - sex hormones - adrenocortical hormones - vitamin D3
Discuss the role of fat in the diet
Palatability - contribute to smell and taste - stimulate appetite - "mouth feel" feels better in your mouth Feeling satiety - increase food time in stomach Concentrated source of energy - 9kcal/g Source of essential FAs Carries fat soluble vitamins
Discuss the role of fat in the body
Energy reserve - main form of stored energy (main for muscle)
Main component of cell membranes
Thermal insulation
Pad internal organs - protect them from shock and trauma
Converted to many other compounds - prostaglandins, thromboxanes, leukotrienes etc.
Outline the dietary requirements of fat
Canadian guidelines:
20-35% of total kcal should come from fat
Include 2-3 tablespoons of unsaturated fats each day
Minimize saturated and trans fats
Eat at least two servings of fish a week
Discuss the role of fat in heart disease
Positive correlation:
Cholesterol is a major component of fatty plaques LDL:HDL ratio
Total fat
Saturated FAs - increase total cholesterol and LDL
Trans fats - raise total cholesterol and LDL levels, lower HDL levels
Negative correlation:
MUFAs & PUFAs (n-3 & n-6) - reduce LDL and triglyceride levels
Omega-3 FAs
- prevent platelet aggregation
- reduce release of cytokines
- reduce serum triglyceride concentrations - 25-30% reduction in TGs with the use of fish oil
