Carbohydrates Part 2- Digestion o Only monosaccharides can be absorbed from the GI tract Except in newborn animals which are capable fo absorbing larger molecules early in their life Have to digest this down or it will end up in the lower digestion and the microbes will use it. We wont get out of it what we need to. o For absorption to occur, di-, tri-. Oligo- and polysaccharides must be hydrolyzed by digestive enzymes from the host or microflora inhabiting the GI tract of host. - Digestion and absorptiono Monogastric Acted upon by enzymes and converted to sugars (primarily glucose) and absorbed across the epithelial cells Carbohydrate utilized starch o Ruminant Cellulose and hemicellulose are utilized - Principle Carbohydrate digestive Enzymes o Maltase, isomaltase, lactase, sucrose Disacchridases Typically gets broken down in to the short chains When it reaches the small intestine (any starch) is acted on by pancreatic amylase Lactase is higher in younger animals- Digestion o Rumen Anaerobic fermentation of carbohydrates by microbes in rumen Almost all carbohydrate is fermented in the rumen - Some “bypass” starch may escape to small intestine- Do not have salivary amylase but has pancreatic amylase to digest starch o Production of Volatile fatty acids (VFA) Mainly acetate, propionate and butyric acids primary Provides a large portion of total energy supply - Can provide 2/3 of energy- propionateo Highly efficient process considering the feedstuffs ingested Cellulose produced by microbes for hydrolysis of cellulose - Breaks the B1-4 glycosidic bond Taking something we could almost not digest on our own to something that we use in a big way. - Microbial populationso Cellulolytic bacteria (fiber digesters) Produce cellulose- cleave B1-4 linages- Cellulose glucose Prefer pH 6-7 (diet mainly forages) Utilize N in form of NH3 Require S for synthesis of sulfur- containing amino acids (cysteine andmethionine) Produce acetate, propionate, little butyrate, CO2- The outcome Predominate in animals fed forage (high fiber diets) o Two groups of bacteria in the rumen o When you feed a diet tailored to this you are enhancing these microbes and selecting for themoo Amylolytic bacteria (starch, sugar digesters) Digest starch Prefer pH 5-6 (we see this in a higher grain level diet) Utilize N as NH3 or peptides Produce propionate, butyrate and sometime lactate Predominate in animals fed grain diets Rapid change to grain diet causes lactic acidosis - Rapid decrease in pH - Streptococcus bovis The starch breakdown - This is why you have to switch from a grain diet to a forage diet easily the change in pH is significant enough - Microbial digestion of carbohydrateso Bacteria attach to (colonize) fiber components and secrete enzymes Cellulose, hemicellulose digested by cellulases and hemicellulases Complex polysaccharides are digested to yield sugars that are fermented to produce VFAso Protozoa engulf starch particles prior to digesting them - Digestion (large intestine) o Carnivores Limited anaerobic fermentation Bacteria produce small quantities of cellulose- Suite of enzymes (also produced by fungi/protozoa)- Cellulose-cellulose glucose Volatile fatty acid (VFA) produced from - Acetate (2C)- Propionate (3C)- Butyrate (4C) There is some production of VFA in small amounts in the large intestine of monogastric animals - Digestion (large intestine/cecum) o Hindgut fermenters - Examples: horse, rabbit (also practices coprophagia) Can utilize large quantities of cellulose Cecum and colon (large intestine) contain bacteria that produce cellulase (cecum and such are very large so time for breakdown and digestion is longer) Increased VFA production Hindgut fermenters have increased capacity to utilized VFA’s for energy - Absorptiono With exception of newborn animal (1st 24 hours), no di-, tri-, or polysaccharides are absorbedo Monosaccharides absorbed primarily in duodenum and jejunum o Limited absorption in the stomach and large intestine - Absorption o Three types of transport systems for nutrients Passive diffusion- simply moving down in concentration gradient (water) - Some lipids more this way Active transport- moves against the gradient - The big one for this - Sodium glucose- cotransporters Facilitated transport- needs a carrier (kind of like a door)- Needs something to literally pick it up and move it- Then it acts like passive diffusion - This is what glucose transporters areo Active transport for glucose and galactose Sodium-glucose co-transporters (SGLT)- Active transport - Glucose is transported against its concentrations gradient by coupling with sodium transport- 6 different SGLT (SGLT-1 to SGLT-6) Glucose transporter (GLUT) - Facilitated diffusion - Present in nearly all mammalian cells - 13 different GLUT (Glut1-Glut12, HMIT)- Sodium- Glucose Co-transporter (SGLT)o What types of energy are we burning are we burning Maintenance Very cell in the body uses this transportation o Facilitated transport Glucose high in the cytosol moves down concentration gradient in to the basolateral membrane (or the blood)---- Absorption/Distribution Overviewo Portal vein or the bloodo First pass through the liver Gives the liver the opportunity to redirect how the excess glucose will be used in the
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