10 Digestion de Carbohidratos.unlocked

7/30/2019 10 Digestion de Carbohidratos.unlocked

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Carbohydrate Digestion


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Digestion and Absorption

Non-ruminant RuminantCHO in feed

digestive

enzymes

Glucose in

small intestine

Absorption into

blood circulation

microbial

fermentation

Volatile fatty acids

in rumen


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Digestion of Carbohydrates

Monosaccharides

Do not need hydrolysis before absorption

Very little (if any) in most feeds Di- and poly-saccharides

Relatively large molecules

Must be hydrolyzed prior to absorption

Hydrolyzed to monosaccharides

Only monosaccharides can be absorbed


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Non-Ruminant Carbohydrate

Digestion Mouth

Salivary amylase

Breaks starches down to maltose Plays only a small role in breakdown becauseof the short time food is in the mouth Ruminants do not have this enzyme Not all monogastrics secrete it in saliva


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Carbohydrate Digestion Pancreas

Pancreatic amylase

Hydrolyzes alpha 1-4 linkages Produces monosaccharides, disaccharides,

and polysaccharides Major importance in hydrolyzing starch and

glycogen to maltose

Polysaccharides DisaccharidesAmylase


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Digestion in Small Intestine Digestion mediated by enzymes

synthesized by cells lining the small

intestine (brush border)

Disaccharides MonosaccharidesBrush Border Enzymes

* Exception is -1,4 bonds in cellulose


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Digestion in Small Intestine

Maltose Glucose + GlucoseMaltase

Lactose Lactase Glucose + Galactose

* Poultry do not have lactase

Sucrose Glucose + FructoseSucrase

* Ruminants do not have sucrase


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Digestion of Disaccharides

Newborns have afull complement of

brush-borderenzymes

Miller et al. (eds.), 1991


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Digestion in Large Intestine Carnivores and omnivores

Limited anaerobic fermentation Bacteria produce small quantities of cellulase SOME volatile fatty acids (VFA) produced bymicrobial digestion of fibers

Propionate Butyrate Acetate


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Digestion in Large Intestine Post-gastric fermenters (horse and

rabbit)

Can utilize large quantities of cellulose Cecum and colon contain high numbers ofbacteria which produce cellulase

Cellulase is capable of hydrolyzing thebeta 1,4- linkage


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Overview Monogastric

Carbohydrate DigestionLocation Enzymes Form of Dietary CHO

Mouth Salivary Amylase Starch Maltose Sucrose Lactose

Stomach (amylase from saliva) DextrinMaltose

Small Intestine Pancreatic Amylase Maltose

Brush Border Enzymes Glucose Fructose Galactose+ + +

Glucose Glucose Glucose

Large Intestine None Bacterial Microflora Ferment Cellulose


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Carbohydrate Absorption in

Monogastrics With exception of newborn animal (first

24 hours), no di-, tri-, or

polysaccharides are absorbed

Monosaccharides absorbed primarily in

duodenum and jejunum

Little absorption in stomach and largeintestine


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Carbohydrates Monosaccharides

Small Intestine

Active

Transport

Liver

Portal Vein

Distributed totissue throughcirculation


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Nutrient Absorption - CarbohydrateActive transport for glucose and

galactose

Sodium-glucose transporter 1 (SGLT1)

Dependent on Na/K ATPase pump

Facilitated transport for fructose


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Carbohydrate Digestion

in Ruminants Ingested carbohydrates are exposed to

extensive pregastric fermentation

Rumen fermentation is highly efficientconsidering the feedstuffs ingested

Most carbohydrates fermented by microbesbefore they can be exposed to typical gastricand small intestinal enzymes


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Microbial Populations Cellulolytic bacteria (fiber digesters)

Produce cellulase - cleaves 14 linkages

Primary substrates are cellulose and hemicellulose Prefer pH 6-7 Produce acetate, propionate, little butyrate, CO2 Predominate in animals fed roughage diets


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ADP

ATP

NADP+

NADPH

Sugars

C

atabolism

Growth

Maintenance

Replication

Microbial Metabolism

VFACO2

CH4

Heat

in rumen:


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a


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VFA Formation2 acetate + CO2 + CH4 + heat

2 propionate + water

1 butyrate + CO2 + CH4

1 Glucose

VFAs absorbed passively from rumen to portal blood

Provide 70-80% of ruminants energy needs


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VFA Production Molar RatiosForage:Grain Acetate Propionate Butyrate

100:0 71.4 16.0 7.9

75:25 68.2 18.1 8.0

50:50 65.3 18.4 10.4

40:60 59.8 25.9 10.2

20:80 53.6 30.6 10.7


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Metabolism of VFA

OverviewAcetate and butyrate are the major energy

sources (through oxidation) Propionate is reserved for gluconeogenesis

Acetate is the major substrate forlipogenesis

Propionate is also lipogenic (though glucose)


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Overview of Carbohydrates and Ruminants

Diet Protein Carbohydrate Fat_____________________________________________

Rumen

_____________________________________________Blood_____________________________________________

Tissue

BacterialProtein

Amino Acids

Protein

Starch VFA

Propionate AcetateButyrate

Glucose

Lactose

Fatty Acids

Fatty Acids

Fat


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