nutrition - lipids

Lipids - General information

• Generally insoluble in water

• Important source of energy (diet, energy storage)

• Cell membrane (lipid bilayer)

  • Microbial phospholipids, mpl, more in abomasum than consumed

• Supply essential FA

  • For synthesis of hormones

Lipids - General information Pt 2

• Used for abs for fat soluble vitamins (ADEK)

• Increase palatability of feed

  • Too much fat decreases palatability (ruminants dislike too much added fat)

• Condition feed (decrease dust, decrease fines as they will clump together → decrease in sorting)

Lipid structure

• Fatty acids: straight chained hydrocarbons

  • Terminate in a methyl group, CH3-(CH2)n-, and in a carbonyl group, -COOH

  • Even number of carbons

• Saturated fatty acids

• Unsaturated fatty acids

Saturated FA (SFA)

• No carbon double bonds (c=c)

• Contain all hydrogens they can contain

  • All the energy they can contain

Unsaturated fatty acids (UFA)

• One or more carbon double bond

• Monosaturated fatty acids (MUFA): 1 c=c, missing 2 hydrogens

• Polyunsaturated fatty acids (PUFA): contain more than 1 c=c, missing 2 hydrogens per double bond

Double bonds determine fluidity

• Increase number of double bonds, decrease melting point (becomes liquid), liquid has more c=c

• Oil= liquid @ room temperature, many double bonds

• Fat= solid @ room temperature, few double bonds

Triacylglycerol = triglyceride (TAG)

• 95% of fat consumed

• 3 position for each glycerol

  • Sn1, Sn2, Sn3

• 3 ester bonds

• Lipase hydrolysis with water TAG to 3 fatty acid and glycerol backbone

• TAG synthesis, expels 3 water and remakes TAG

Phospholipid

• Glycerol backbone

• Hydrophobic section

  • Sn1, Saturated fatty acid, no c=c and 4 carbons entirely

  • Sn2, Unsaturated fatty acid, 1 c=c, 12 carbons in total

• Hydrophilic section

  • Sn3, polar head group with phosphorus

Non ruminant lipid digestion

• TAG(Triacylglycerol) with lipase + H2O → DAG (diacylglycerol) + FFA

• DAH with lipase + H2O → MAG (monoacylglycerol) + FFA

• Small intestine absorbs FFA (free fatty acids)

Non ruminant lipid digestion - stomach activity

• Lingual lipase: produced by salivary glands, active in stomach

• Gastric lipase : produced by chief cells in stomach

• Shared characteristics of LL and GL

  • Produced continuously, production increases with increased fat intake

  • Both are stable and active at low pH of stomach

  • Prefer Hydrolyzes short to medium chain FA

  • Act on FA at sn3 position

Emulsification and 2 types

• Increase surface area of fat droplets by making many small fat droplets

• Physical emulsification: takes place in stomach and small intestine

  • Mixing of food/digesta and movement of food/digesta into SI

• Chemical emulsification: takes place in SI, maintains small fat droplets

  • Facilitated with bile (made of cholesterol, stored in gallbladder, synthesized in liver) coats fat droplet to stabilize it

  • Bile is amphipathic, hydrophobic and hydrophilic

Non ruminant lipid digestion - Proteins in Si to digest TAG

• Pancreatic lipase: Hydrolyze FA from TAG at sn1 and sn3 position

• Procolipase: not an enzyme, produced by pancreas, activated to colipase by trypsin

  • Procolipase with trypsin → colipase

• Colipase: has hydrophobic region that can interact with fat droplet

  • Creates binding site for pancreatic lipase

Non ruminant lipid digestion - mouth digestion of TAG

• Mouth, minimal digestion (TAG)

  • Lingual lipase in mouth (sn3 position on TAG)

  • Decreases particle size

  • Hydrolyzes TAG into DAG with LL and water

Non ruminant lipid digestion - stomach digestion

• Mostly TAG, some DAG, FFA

• Gastric lipase sn3, physical emulsification

• TAG hydrolyzed with lingual lipase and gastric lipase with water to produce DAG

Non ruminant lipid digestion - small intestine

• Mostly TAG, some DAG and FFA

• 3 phases

  • 1. Emulsification: physical (mixing), chemical (bile)

  • 2. Enzymatic: pancreatic lipase (sn1 and sn3 position), procolipase with trypsin → colipase

    • TAG is hydrolyzed with pancreatic lipase with water to produce FFA and DAG, and the again to produce FFA and monoacylglycerol

      • Sn2 position left with FA

  • 3. Absorption, MAG + 2FFA (diffuse into enterocyte, no transporters)

    • Bile absorbed in ileum

    • Li/cecum, undigested lipids and acted on by microbes

    • Almost all lipid absorb in small intestine

    
    

Lipid digestion in enterocyte - FA

• FA less than or equal to 10 carbons, move through enterocyte and directly enter the blood

  • In the blood, albumin binds FA and takes it to liver

• FA more than or equal to 12 carbons, subjected to intracellular TAG reformation

  • MAG + FFA → releases H2O → DAG + FFA → releases H2O → TAG

  • Done by acylCOAsynthetase

Endoplasmic reticulum

• Accumulate TAG, ADEK, cholesterol into fat particle

• Add protein, B48, to particle

  • B48: apolipoprotein that stabilizes lipoprotein (fat particle), confers specificity (name tag, exogenous lipid), and enables lipoprotein lipase to hydrolyze TAG into DAG and FFA

  • Lipoprotein lipase: located on surface of muscle and adipose tissue

Lipid digestion in enterocyte - Golgi apparatus and chylomicron

• Lipoprotein is pinched off as lipid vesicle

• Golgi apparatus, CHO attached to lipoprotein → chylomicron

• Chylomicron: complete fat particle (82% TAG, 7% phospholipid, 2% cholesterol, ADEK, 9% protein)

  • Exocytosed into lymphatic circulation into blood slowly

• Lipoprotein lipase takes TAG and makes it into DAG and FFA in muscle and adipose tissue

  • Used for energy and storage

• Chylomicron remnant: devoid of TAG, removed by liver and metabolizes it

Proteins summary

• Lingual lipase: is in stomach, breaks ester bond and does TAG digestion

• Gastric lipase: stomach, breaks ester bond and does TAG digestion

• Pancreatic lipase: in small intestine, breaks ester bond and does TAG digestion

• Procolipase (not enzyme): small intestine, activated to colipase by trypsin and helps PL

Proteins summary Part 2

• Trypsin: small intestine, activates Procolipase to colipase

• AcylCOAsynthetase: in enterocyte, synthesizes TAG to in enterocyte

• B48 (not enzyme): in chylomicron; stabilizes, names, and allows lipoprotein lipase to work

• Lipoprotein lipase: in muscle and adipose tissue, takes TAG and hydrolyzes it to DAG and FFA

• Albumin: not an enzyme, in blood and transports FA less than 10 carbons to liver

Pig digestion lipids - mouth and stomach

• In mouth TAG is consumed, mouth reduces particle size and produces lingual lipase (attacks sn3 position of TAG)

• Gastric lipase produced in stomach, attacks sn3 position of TAG

• In stomach, through lingual lipase or gastric lipase and water, TAG is hydrolyzed to mostly TAG but some DAG and FFA

• In stomach, physical emulsification occurs

Pig digestion lipids - liver, pancreas, duodenum

• Bile is produced in liver which is stored in gallbladder, then goes to duodenum

  • Enterohepatic recycling of bile from ileum (absorbed ) and sent back to liver

• Pancreas produces pancreatic lipase and procolipase

• Fat droplet in duodenum (TAG, DAG, and FFA), CL and PL attached to fat droplet

• In duodenum, there is physical and chemical emulsification (bile)

Pig digestion lipids - jejunum

• Through absorption and digestion of lipids, 2FFA and MAG released in jejunum

• In jejunum, procolipase to colipase by trypsin

• In enterocyte, fatty acids with less than or equal to 10 carbons and transported into blood by albumin

• Also in enterocyte, fatty acids with more than or equal to 12 carbons and MAG are converted into TAG by acylCOAsynthetase, which turns into chylomicron

  • Exocytosed into lymphatic and then enters blood

  • Chylomicron through blood is sent to muscle and adipose tissue for energy or fat synthesis

  • Chylomicron is also hydrolyzed into DAG and FFA through lipoprotein lipase

  • Chylomicron remnant is sent to liver

Pig digestion lipids - ileum and large intestine

• Bile from ileum used for enterohepatic recycling to liver

• In large intestine mpl synthesis is excreted

• In large intestine, after digestion and absorption of lipids, two things occur:

  • 1. Hydrolysis, making ester bonds, produces glycerol which produces VFA (B) is then absorbed

  • 2. UFA → SFA through hydrogenation (addition of H2), excreted

Enterocyte - lipid digestion

• Fat droplet with TAG, FFA, and MAG

• FA with less than or equal to 10 carbons diffused into enterocyte and then goes into blood (binded with albumin) to liver

• FA with greater than or equal to 12 carbons and MAG converted to TAG with acylCOAsynthetase

  • Produces release of 2H2O, helps produce 2 ester bonds for TAG

• TAG goes to endoplasmic reticulum and accumulates, B-48 bound to TAG

• TAG goes to Golgi apparatus and now has carbohydrates attached to it, becomes Chylomicron

• Chylomicron is Exocytosed from enterocyte and enters lymphatic and into blood with time

• Chylomicron enters muscle and adipose tissue and then becomes Chylomicron remnant (devoid of TAG) and goes back to liver

• With lipoprotein lipase and water, TAG from Chylomicron is hydrolyzed into DAG and FFA and absorbed into muscle and adipose tissue