2 Nut: Lipids

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gen

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definition:
- organic compounds in plants and animals that are insoluble in water, but soluble in ether, chloroform, or benzene
- contain more H than CHO
- also P and some N
- fats, oils, sterols, phospholipids, waxes

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fx

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1. concentrated form of E: 9kcal/g
2. insulation
3. organ padding
4. structural cellular and subcellular components
5. hormones, precursors for prostaglandin synthesis
6. added to diets: inc abs of fat soluble nutrients (sterols, vitamins), reduce dustiness of feed

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levels of fat in typical diets

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levels of fat in typical diets:
1. R: very low, <5%
2. pigs, poultry: < 10%
3. cats and dogs: 20-30%
4. humans: 10-25%

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essential fatty acids

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essential fatty acids:
- needs met with little dietary fat: <1%
1. linoleic acid: 18:2 (o6)
- grains, plants, animals
2. linolenic acid: 18:3 (o3)
- plants, low in animals
3. arachadonic acid: 20:4 (o6)
- animal tissues only

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signs of EFA deficiency

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signs of EFA deficieny:
- not seen in R because EFA made by bigs
1. skin lesions
2. repro failure
3. edema
4. subcutaneous hemorrhage

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solubility

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solubility:
- key requirement for fat digestion
- enhanced by micelles, chylomicra, lipoproteins

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bile

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bile:
- allows for solubility
- contains: bile salts, phospholipd, cholesterol, and bicarbonate
- stored in gall bladder, secreted into duodenum and recycled into liver via enterohepatic circulation
- increases pH
- bile salts act as detergents to emulsify lipids for lipase action

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absorption

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absorption:
- primarily in jejunum
- largely passive
- most SCFA directly into portal blood

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reassembly of TG

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- re-assembly of TG:
into enterocyte and formation of chylomicron into lymphatic vessels

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bile acid and cholesterol excretion

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bile acid and cholesterol excretion:
- 1-5% ba and cholesterol are not absorbed in jejunum or ileum
- high fiber diets promote

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secretions that aid lipid digestion

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secretions that aid lipid digestion:
1. salivary and gastric lipase (mammals only): TG + H2O --> DG + FA --> MG + FA
2. pancreatic juice: lipase, phospholipase, cholesterol esterase, bicarbonate
3. intestinal lipase: from enterocytes
TG + H2O --> 2MG + 2FFA

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lipoprotein structure

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lipoprotein structure:
- hydrophobic core of triglyceride and cholesterol esters (non-polar)
- hydrophilic (charged) outside

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lipoprotein classification

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lipoprotein classification:
1. chylomicron
2. VLDL
3. LDL
4. HDL
- fx: transport lipids to tissues

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chylomicron

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chylomicron (lipoprotein):
- made in intestine, very TG rich
- called portomicron in birds

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VLDL, LDL and HDL

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lipoproteins: transport lipid to tissues
1. VLDL: TG rish
2. LDL: less TG
3. HDL: much less TG, takes cholesterol from tissue to liver
- all from liver

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lipogenesis

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lipogenesis:
- series of pathways required for triglyceride synthesis
- need FA + glycerol
- anabolic

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beta oxidation

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beta oxidation:
- pathway for oxidation of FAs
- 2 carbon units are liberated at a time to generate acetyl-CoA
- further oxidation in the TCA cycle
--> CO2

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fatty liver syndrome

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fatty liver syndrome:
- abnormal accumulation: normal 5% fat vs FLS >30%
1. high fat or carb diets
2. excessive lipid mobilization
3. impaired lipid transport from liver
4. liver damage: infection, poisons, cirrhosis

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abnormalities in lipid metabolism

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abnormalities in lipid metabolism :
1. genetics
2. behavior
3. caloric intake
4. endocrine system
5. lack of exercise

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simple lipids

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simple lipids:
- esters of fa's with vario`us alcohols
- eg triglycerides

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complex lipids

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complex lipids:
- esters of fa's containing groups in addition to alcohol
1. phospholipids: phosphoric acid residue and N-containing bases
2. glycolipids: sphingosine and carb
3. others: sulfolipids, aminolipids, lipoproteins

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sterols

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sterols:
- lipids with phenanthrene type ring stuctures
- cholesterol: substrate to make: bile, vit D, steroid hormones

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Fa's

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fa's:
- hydrocarbon chains of 2-24C
- most even #C, but bacteria odd #C and even branched
- saturated or unsaturated
- acetic: CH3COOH C2:0
- myristic: CH3(CH2)12COOH, C14:0

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fa examples

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fa examples:
- abbrev: #C: #double bonds
- following are all octadecanoic
1. stearic acid: C18:0
2. oleic acid: C18:1
3. linoleic: C18:2
4. linolenic: C18:3

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fas in plants vs animals

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fa's:
1. plants: unsaturated
- grain: high C18:2
- hay: high C18:3
2. animals: monunsaturated and saturated
- high C16:0 and 18:1

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lipid digestion in R

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lipid digestion in R:
1. bugs hydrolyze TG and forage galactolipids, releasing ffa's
2. glycerol and galactose converted to VFA
3. rumen reducing environment, bugs hydrogenate fa's to more saturated state
4. new fa's made by bugs
5. compared to NR, fa's arriving in SI are very different from that of their diet

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factors influencing absorption

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factors influencing absorption:
1. saturation: decreases digestibility
2. chain length: >18C dec dig
3. amount: high dec dig and abs
4. overheating and autooxidation: rancidification of double bond
5. Ca: optimal level= optimal abs, but high Ca dec abs

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fat synthesis

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fat synthesis:
1. fa and tg syn: adipose of mammals, liver of birds (then transp to adipose)
2. fa in adipose tg: from blood lipoprotein de novo synthesis
3. liver, muscle and other tissues: oxidize fa

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substrate for triglycerides

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substrate for triglycerides:
1. NR: glucose
2. R: acetate

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post meal

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post meal:
1. high fat: numerous chylomicrons in blood
- low ffa, lipogenesis primarily from dietary fa's
2. high carb: lipogenesis from glc or acetate, less chylomicrons in blood
3. post-absorbative state: chylomicrons low
- lipolysis begins: inc ffa in blood to supply tissues E
- LDL synthesis

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changing body lipids

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changing body lipids
- genes more than diet control types of fa's synthesized
- can easily change amount of fat
1. NR: alter body fat composition somewhat, genes limit
2. R: need to feed "protected lipids" to avoid rumen hydrogenation, allows modest change in proflie

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lipid metabolism

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lipid metabolism:
- liver central organ, lipoproteins important
1. lipolysis and beta oxidation
2. lipogenesis and esterification of fa to glycerol