30 - Carbohydrate Digestion, Absorption And Metabolism

Front 1

Oral CHO digestion in monogastrics: mechanisms and what they do

Back 1

Mastication - decreases particle size and increases area for enzyme digestion

Salivary amylase - Converts starch to maltose and smaller oligosaccharides

Front 2

In which species does Amylase has a minor role in CHO digestion?

Back 2

Pigs and Dogs

Front 3

Corpus and Fundus CHO Digestion for monogastrics: mechanisms and how they work

Back 3

Salivary amylase converts starch to maltose and smaller oligosaccharides (*important in pigs)

(amylase rapidly inactivated by low pH)

Front 4

Intestinal CHO digestion in monogastrics

Back 4

Pancreatic amylase converts remaining starch and polysaccharides to monosaccharides

Front 5

What percentage of starch breakdown occurs in the:

Oral cavity?

Corpus/Fundus?

Intestines?

Back 5

Oral: ~5%

Corpus/Fundus: ~30%

*Remainder in the intestines

Front 6

Phases of intestinal digestion

Back 6

Luminal phase

Membranous phase

Front 7

Luminal Phase:

-Where are the enzymes active?

-What occurs during this phase (overview)?

Back 7

Enzymes active in gut lumen

Large polymers like starch and protein digested

by digestive enzymes from salivary, gastric and pancreatic glands

Front 8

Membranous Phase:

-Where are the enzymes active?

-What occurs during this phase (overview)?

Back 8

Enzymes active at surface of gut

Small polymers like polysaccharides and peptides digested by digestive enzymes synthesized in enterocytes and attached to apical membrane

Front 9

Specific starch digestion phases in the intestine

Back 9

Pancreatic Phase

Mucosal Phase

Delivery Phase

Front 10

What occurs during pancreatic phase?

Back 10

alpha-amylase from pancreas breaks down starch into glucose (first goes through a-dextrine, maltotriose, maltose)

Lactase breaks down lactose into galactose and glucose

Front 11

What occurs during mucosal phase?

Back 11

Glucose is taken up into intestinal epithelium by the transporter: SGLT1 on brush border

Glucose can also move through paracellularly (paracellular diffusion)

Front 12

What happens in delivery phase?

Back 12

Glucose in the epithelial cell undergoes metabolism for cell functions

Glucose gets transported out of cell and into the portal circulation through the transporter: GLUT2

Front 13

Where does the energy for the SGLT1 come from?

Back 13

Na-K ATPase transporter

Front 14

Name sodium-glucose co-transporters

Back 14

SGLT1

SGLT2

SGLT3

Front 15

SGLT1:

-Found in which major tissues?

-Functions?

Back 15

Kidney, Intestine

Glucose reabsorption in intestine and kidney

Front 16

SGLT2:

-Found in which major tissues?

-Functions?

Back 16

Kidney**

Low affinity but high selectivity for glucose

Front 17

SGLT3:

-Found in which major tissues?

-Functions?

Back 17

Small Intestine, Skeletal muscle

Glucose activated Na+ channel

Front 18

Facilitative Glucose Transporters: name the important ones

Back 18

GLUT1, GLUT2, GLUT4, GLUT5

Front 19

GLUT1:

-Found in which major tissues?

-Functions?

Back 19

Ubiquitous: RBCs, Brain, Eye, Mammary

Basal glucose uptake and transport across blood tissue barrier

Front 20

GLUT2:

-Found in which major tissues?

-Functions?

Back 20

Liver, Kidney, Pancreas, Small Intestine

High capacity, low-affinity transport

Front 21

GLUT4:

-Found in which major tissues?

-Functions?

Back 21

Muscle, Fat, Heart

Insulin-regulated transport in muscle and fat

Front 22

GLUT5:

-Found in which major tissues?

-Functions?

Back 22

Intestine, Kidney, Testis

Fructose transport

Front 23

What are CHOs good for in Ruminants

Back 23

Major energy source

-50% of grain fed to animals

-60-70% total diet in dairy cattle

Front 24

Main functions of CHOs in ruminants?

Back 24

Energy for microbes and host

Maintain a healthy GIT

Front 25

CHO fermentation productions in ruminants?

Back 25

VFAs: Acetate, Proprionate, Butyrate

Front 26

Ruminal digesta fractions and what they contain

Back 26

1. Fibrous raft - high density of microbes

2. Liquid fraction - shuttles saliva & fermentation end products in and out

3. Boundary layer against lumen surface - bidirectional fluid exchange

4. Soupy Material - provides cud and material for omasum

Front 27

Where is soupy material found?

Back 27

Ventral and cranial sacs

Front 28

Define: Fermentation

Back 28

A slow, digestive process of anaerobic digestion by microbial enzymes

Front 29

Synergy between host and microbes: what does each provide the other?

Back 29

Host provides environment (substrate, H20, pH, redox conditions, slow digesta flow)

Microbes convert indigestible material into useful products for host (VFAs, CH4, NH3, CO2, Microbial cells and LCFA)

Front 30

What are the requirements for fermentation?

Back 30

1. Substrate (regular supply of new feed)

2. Microbes (suitable numbers and types)

3. Mixing and propulsion (helps fermentation)

4. Fermentation end products (steadily removed)

5. Stable intraruminal conditions

Front 31

What are stable intraruminal conditions?

Back 31

Optimum temperature: 37'C

Osmolality: 300 mOsm

pH: 6.4

Anaerobic conditions: most microbes are strictly anaerobic; -ve oxidation reduction potential

Front 32

Rumen protozoa: digestion and fermentation

Back 32

-Engulf feed particles, digest and store CHO, proteins and fat

-Ingest bacteria

-Produce some VFAs and NH3

-Slow digestion of rapidly fermentable starches and proteins

Front 33

Rumen protozoa decrease significantly when?

Back 33

High grain diets are fed and pH <5.5

Front 34

Advantages of rumen protozoa

Back 34

1. Store starch particles, thereby preventing rapid degradation by amylolytic bacteria

2. Reservoir of microbial protein

3. Provide host with protein, stored starch and PUFA when digested

Front 35

Types of rumen bacteria based on location

Back 35

1. Free-living in the liquid phase

2. Loosely/firmly associated with feed particles

3. Associated with rumen epithelium

4. Attached to surface of protozoa and fungi

Front 36

Types of rumen bacteria based on fermentation

Back 36

1. Primary bacteria

2. Secondary bacteria

Front 37

Primary bacteria:

What do they do?

Examples?

Back 37

Directly break down digesta

-Cellulytic (18h doubling time, slow metabolism, Opt. pH ~6.5)

-Amylolytic (<4h doubling time, Opt. pH 5.5-6.8)

Front 38

Secondary bacteria:

What do they do?

Examples?

Back 38

Feed on by-products of primary bacteria (16h doubling time, Optimum pH 6.2-6.8)

Propionate bacteria - utilize lactate

Mathanogenic bacteria - utilize H2

Front 39

Process of rumen bacterial attachment to plants

Back 39

1. Free bacteria move to fibrous substrate

2. Initial non-specific adhesion on cut surfaces (electrostatic/ionic)

3. Specific adhesion (ligands/adhesins on bacterial surface)

*Proliferation and colonization on feed

Front 40

What happens to cellulose digestion if unsaturated fat is fed?

Back 40

It leads to decreased cellulose digestion due to interference of bacterial attachment to substrate

Front 41

Benefits of bacterial attachment to plants

Back 41

1. Brings enzyme & substrate together

2. Protects enzymes from proteases in rumen

3. Allows bacteria to colonize the digestible surface of feed particles

4. Retention in the rumen to prolong digestion

5. Reduces predatory activity of protozoa

Front 42

Function of protozoa

Back 42

Ingest and digest feed particles producing VFA, CO2 and NH3

Also keeps bacteria in check

Front 43

Protozoal storage

Back 43

Feed particles like CHO, fat and protein to prolong digestion

Front 44

Location of protozoa

Back 44

Both liquid and solid phases

Front 45

Number and size of protozoa

Back 45

10^4 - 10^6 cells/gm of rumen contents

~51% of microbial volume

Front 46

pH sensitivity of protozoa

Back 46

Highly pH sensitive so they decreases in number on high grain diets

Front 47

Function of bacteria

Back 47

Ferment CHO, fat and protein to produce VFA, CO2 and NH3

Front 48

Bacterial storage

Back 48

Very limited/no storage capacity

Front 49

Location of bacteria

Back 49

Free living in rumen fluids, or

Loosely/firmly attached to feed particles, or

Attached to rumen epithelium (mainly fungi for fibre digestion)

Front 50

Number and size of bacteria

Back 50

10^10 - 10^12 cells/gram of rumen contents

~40% of microbial volume

*much smaller in size than protozoa

Front 51

pH sensitivity of bacteria

Back 51

Some strains are pH resistant

Front 52

In a high forage: low concentrate diet, which VFAs are produced and relative quantity?

In a low forage: high concentrate diet, which VFAs are produced and relative quantity?

Back 52

Mainly acetic acid, some acetic acid, the least butyric acid

Mainly propionic acid, some acetic acid, the least butyric acid

*butyric acid stays constant

Front 53

Which VFA is the gluconeogenic one?

Back 53

Propionate

Front 54

How are VFAs transported from rumen fluid into the epithelial cells?

Back 54

1. Simple diffusion (butyrate)

2. HCO3-/SCFA- antiporter

3. Lactate/H+ symporter

Front 55

What happens in the rumen epithelial cell after VFAs enter?

Back 55

Some HSCFA get broken down into SCFAs and then into KETONES

Front 56

Main transporter for ketones from rumen epithelial cell into the blood?

Back 56

MCT1

Front 57

Methods of VFA absorption into the blood (across basolateral membrane)?

Back 57

1. Simple diffusion (HSCFAs)

2. Cl-/SCFA- antiporter

3. HCO3-/SCFA- antiporter

4. MCT1

Front 58

VFA disassociation curve

Back 58

Front 59

4 stages of VFA synthesis

Back 59

Hydrolysis

Glycolysis

VFA synthesis

Microbial protein synthesis

Front 60

Precursors for:

Acetate

Butyrate

Propionate

Back 60

Phosphenol pyruvate

Acetyl CoA

Oxaloacetate & Lactate

Front 61

Amount of Ruminal epithelial metabolism of VFAs and what it produces

Back 61

90% Butyrate --> Ketone bodies (alimentary ketogenesis)

70% Prpionate --> lactate + CO2 + amino acids

30% acetate

Front 62

Energy production, in ATP/mol, for each VFA

Back 62

Acetate: 10

Propionate: 18

Butyrate: 27

Front 63

Which VFAs are not used for net glucose synthesis?

Back 63

Acetate and Butyrate

Front 64

What does acetate provide?

Back 64

Carbon source for fatty acids in adipose and mammary gland

Front 65

What does propionate provide?

Back 65

Glucose

Stimulates INSULIN secretion

5% converted to lactate

Front 66

What does butyrate provide?

Back 66

Carbon source for fatty acids in mammary gland

Stimulates INSULIN and GLUCAGON secretion

Critical for rumen papillae growth

Front 67

What is Parakeratosis?

What are events leading up to it?

Back 67

Excessive keritinization of the epithelium

Increase in fermentable CHO feeding initially causes sloughing of stratum corneum leading to parakeratosis and formation of stellate ulcers

Front 68

Major type of bacterium in animals fed high grain diets

Back 68

Amylolytic

Front 69

Examples of Ruminal bacteria that rapidly ferment starch/soluble sugars

Back 69

Selenomas ruminantium

Streptococcus bovis

Lactobacillus species

Front 70

Describe S. ruminantium

Back 70

Dominant organism that makes up 22-51% of culturable bacteria in the rumens of high-grain diet animals

Front 71

Describe S. bovis

Back 71

A facultative anaerobe that has explosive growth in response to availability of fermentable CHO especially when animal unadapted to high grain

Has a rapid growth rate and rapidly degrades cereal grain starches

Front 72

Lactic acid production by S. bovis causes what?

Back 72

Decrease in ruminal pH which inhibits growth rates of most ruminal bacteria

This causes acid-tolerant Lactobacilli to predominate

Front 73

Describe lactobacilli

Back 73

Predominant organism in acidotic rumens

Lactic acid producing!

Front 74

Sequellae of rumen acidosis

Back 74

Rumenitis (stellate ulcers)

Liver abscesses (F. Necrophorum)

Diarrhea due to increased osmolality of fluids

Laminitis

Sudden death from dehydration, acidosis, endotoxemia

Front 75

Glycogenesis - Glycogenolysis: Liver vs. Muscle

Back 75

Liver has glucose-6-Pase enzyme to produce glucose

Muscles don't have enzymes to sythesize glucose from lactate so glycolysis occurs and lactate then transported into liver

*Liver takes up lactate and undergoes gluconeogenesis to produce glucose

Front 76

Rate limiting enzymes for glycogenesis

Back 76

Glycogen synthetase

Front 77

Rate limiting enzymes for glycogenolysis

Back 77

Glycogen phosphorylase

Glucose-6-Phosphatase (G-6-Pase_

Front 78

What happens during Cori cycle?

Back 78

Lactate from muscle is transported into liver via blood - Gluconeogenesis from lactate in liver - glucose returned to muscle via blood

Front 79

Sources for gluconeogenesis for ruminants

Back 79

Propionate

Amino acids

Lactate

Glycerol

Front 80

In ruminants, gluconeogenesis meets ________ of total glucose needs

Back 80

75-90%

Front 81

Gluconeogenesis sources in carnivores

Back 81

Amino acids

Front 82

Gluconeogenesis sources during anaerobic exercise

Back 82

Muscle lactate (Cori cycle)

Front 83

Plasma glucose differences between ruminants and carnivores

Back 83

50-60mg/dl in ruminants (very stable levels)

100mg/dl in carnivores (fluctuations after meals)

Front 84

Principle types of Hypoglycemia

Back 84

1. Insufficient gluconeogenesis & glycogen stores

2. Mesenchymal tumors

3. Glycogen storage diseases

4. Hyperinsulinemia

Front 85

Insufficient gluconeogenesis and glycogen stores most common in? why?

Back 85

Ruminants during pregnancy and lactation

Neonatal pigs

Adrenal cortex/anterior pituitary deficiency

Liver diseases

Front 86

Why do Mesenchymal tumours cause hypoglycemia?

Back 86

Inhibits glucagon

Front 87

Hyperinsulinemia: how does it occur (pathway)? Name phenomenon?

Back 87

Somogyi overswing

Insulin overdose - hypoglycemia - increase glucagon and cortisol secretion - hyperglycemia and glucosuria

Front 88

Hyperinsulinemia in dogs

Back 88

Organic: Islet tumours

Functional: Insulin secretion normal at fasting, but hypersecretion after CHO ingestion

Front 89

Principle types of hyperglycemia

Back 89

Diabetes Mellitus

-Type 1: juvenile or IDDM

-Type 2: adult onset or NIDDM

-Other types

Front 90

What causes Type 1 DM

Back 90

Primary insulin deficiency

Beta-cell failure (autoimmune disorder)

Common in dogs and cats

Front 91

What causes Type 2 DM

Back 91

Primary insulin resistance

Beta-cell exhaustion and atrophy

Typical in humans, less common in dogs and cats

Early lactation cows can have it too

Front 92

Other types of DM

Back 92

Gestational diabetes

Diestrus diabetes