Carbohydrates Pt. 2

ANSC 311 - Lecture 6

do monosaccharides need hydrolysis before absorption?

no

do di- and polysaccharides need hydrolysis before absorption?

yes, they are hydrolyzed to monosaccharides

function of salivary amylase

• breaks starches down to maltose

• ruminants do not have this enzyme

• not all monogastrics secrete it in saliva

pancreatic amylase

• hydrolyzes alpha 1-4 linkages

• produces monosaccharides, disaccharides, and polysaccharides

• major importance in hydrolyzing starch and glycogen to maltose

how is digestion mediated in the small intestine?

it’s mediated by enzymes which are synthesized by cells that line the small intestine (brush border enzymes)

what animals do not have sucrase (enzyme that breaks down sucrose)?

ruminants

what enzyme breaks down maltose?

maltase

what animal does not have lactase (enzyme that breaks down lactose)?

poultry

__________ have a full complement of brush-border enzymes

newborns

what kind of animal has limited anaerobic fermentation?

carnivores and omnivores

what are examples of post-gastric fermenters?

horse and rabbits

in carnivores and omnivores, what does bacteria produce in the large intestine?

small quantities of cellulase

what can post-gastric fermenters utilize large quantities of?

cellulose

in post-gastric fermenters, where is the bacteria that produces cellulase located?

cecum and colon

how do newborns get their carbohydrates?

through mothers’ milk (lactose)

where are monosaccharides primarily absorbed in monogastrics?

the duodenum and jejunum (small intestine)

in monogastrics, how are monosaccharides taken up (absorbed)?

taken up by active transport or facilitated diffusion and carried to the liver

what cells is glucose transported to?

cells that require energy

what influences the transportation rate of glucose?

insulin

what kind of animal has pregastric fermentation?

ruminants

pregastric fermentation

most CHO fermented by microbes before they can be exposed to typical gastric and small intestinal enzymes

true or false: rumen fermentation is highly efficient considering the feedstuffs ingested

true

what are the 3 main VFA’s produced?

propionate, butyrate and acetate

in ruminants, where are most CHO fermented?

rumen

true or false: ruminants have salivary and pancreatic amylase

false, they only have pancreatic amylase

cellulolytic bacteria (fiber digesters)

• produce cellulase

• prefers 6-7 pH

• utilize N in form of NH3

• produce 3 main VFA’s and CO2

• predominate (main element) in animals fed roughage diets

amylolytic bacteria (starch, sugar digesters)

• digest starch

• prefer 5-6 pH

• utilize N as NH3 or peptides

• produce propionate, butyrate and sometimes lactate

• predominate in animals fed grain diets

function of microbes in the rumen

attach to (colonize) fiber components and secrete enzymes

what are polysaccharides broken down into in the rumen?

digested to yield sugars that are fermented to produce VFA

what is more rapidly fermented to VFA in the rumen?

starches and simple sugars

ruminant CHO digestion in the small intestine

• secretion of digestive enzymes

• digestive secretions from pancreas and liver

• further digestion of CHO

• absorption of H2O, minerals, amino acids, glucose and fatty acids

ruminant CHO digestion in the cecum and large intestine

• bacterial population ferments the unabsorbed products of digestion

• absorption of H2O, VFA and formation of feces

what provides 70-80% of ruminant’s energy needs?

VFA’s

in rumens, what are the primary byproducts of rumen fermentation?

gases (CO2 and methane)

bloat

severe distension of the rumen, typically on the left side

uses of VFA acetate

• energy

• fatty acid synthesis

uses of VFA propionate

• energy

• gluconeogenic - glucose synthesis

uses of VFA butyrate

• energy

• rumen epithelial cells convert to ketone

what do the proportion of VFA’s produced depend on?

diet

in rumens, where does VFA metabolism take place?

in the rumen wall

what VFA do cells use most of for their own energy needs?

butyrate

what VFA’s are exported to the blood?

acetate and propionate

in ruminants, what are the major energy sources?

acetate and butyrate

what is propionate reserved for?

gluconeogenesis

what is the major substrate for lipogenesis?

acetate

there is less fluctuation in blood/glucose in ruminants, why?

• eat more constantly than monogastrics

• continuous VFA production

• continuous digesta flow

• continuous gluconeogenesis