Topic 56 - Catabolism and absorption of carbohydrates

Question 1

Words to include in catabolism of carbohydrates

Answer 1

• Starch
  
  • Enzyme
  • Glucose molecules
  • α-1-4 glycosidic bonds
  • α-1-6 glycosidic bonds
  • Oral cavity
    
    • Saliva ptyalin
    • Maltose
    • Maltotrase
    • Dextran
  • Stomach
  • Small intestines
    
    • Bi-phasic process
    • α-amylase
    • Pancreatic juice
    • Disaccharides
    • Oligosaccharides
    • Brush border digestion
    • Enterocyte
    • Monosaccharides
    • Absorption
• Cellulose
  
  • Microbial fermentation
  • Fibrous carbohydrate
  • Cleaved
  • Microbial enzymes
  • Volatile fatty acids
    
    • Acetic acid
    • Propionic acid
    • Butyric acid
  • Osmotic pressure
  • Colon
  • Ruminant:
    
    • Microflora of rumen
      
      • Protozoa
      • Bacteria
    • Fermentation
      
      • Volatile fatty acids
    • Deaminate amino acids
      
      • Branched fatty acids
    • Urease
    • Carbamine
    • NH₃^-
• Microbial digestion
• Auto-enzymatic digestion

Question 2

Words to include in absorption of carbohydrates

Answer 2

• Fructose
  
  • GLUT-5 transporter
  • Luminal membrane
  • Basolateral membrane
• Glucose / galactose
  
  • Secondary transport mechanism
  • Luminal receptor
  • Na⁺
  • Conformational change
  • Cytoplasm
  • GLUT-2 transporter
  • Basal membrane
  • Interstitium
  • Facilitated transport

Absorption from ruminant stomach:

• Volatile fatty acids
  
  • Carbohydrate fermentation
  • pH
  • Rumen
• Lactic acid
  
  • Acidosis
  • Rumen
• Ammonia
  
  • Urea
  • Protein
  • Rumen
  • Liver
  • V. porta

Question 3

Topics to include in the essay

Answer 3

1. Catabolism of carbohydrates
   
   • Microbial digestion VS auto-enzymatic digestion
   • Starch
   • Cellulose
   • Digestion of carbohydrates in ruminants
     
     • Microflora in rumen
     • Fermentation
2. Absorption of carbohydrates
   
   • Fructose
   • Glucose / galactose
   • Absorption from ruminant stomach
     
     • Volatile fatty acids
     • Lactic acid
     • Ammonia

Question 4

Catabolism of carbohydrates

General

Answer 4

• Eg. starch, can be digested by the enzymes produced by the animal
• Eg. cellulose, can only be digested by microbial fermentation
• Difference between microbial and auto-enzymatic digestion:
  
  • Fibrous carbohydrates which can not be digested by mammalian enzymes can be cleaved by microbial enzymes

Question 5

Carabolism of carbohydrates

Starch

Answer 5

• Composed of glucose molecules bould together by:
  
  • α-1-4 glycosidic bonds (straight chains)
  • α-1-6 glycosidic bonds (branched chains)
• Oral cavity:
  
  • Saliva ptyalin will cleave the straight chains of the starch
  • Smaller and branched molecules are produced:
    
    • Maltose
    • Maltotrase
    • Dextran
• Stomach
  
  • The effect of salivary amylase last until the gastric content is mixed
  • Amylase is denaturated
• Small intestines
  
  • Bi-phasic process
  • α-amylase of the pancreatic juice hydrolyses starch to:
    
    • Disaccharides
    • Oligosaccharides
  • Brush border digestion

Question 6

Catabolsim of carbohydrates

Cellulose

Answer 6

• Fibrous carbohydrates
• Can not be digested by mammilian enzymes
  
  • Must be cleaved by microbial enzymes
• Herbivore (eq):
  
  • End product: volatile fatty acids (about 75% of energy in eq)
  • Location: colon
• Carnivores:
  
  • Not much cellulose, but microbila fermentation in colon is important (non-digested carbohydrates would be lost if not)
  • Unabsorbed carbohydrated in colon → osmotic pressure → loss of water

Question 7

Catabolism of carbohydrates

Ruminants

Answer 7

• Microflora in rumen:
  
  • Competition between protozoa and bacteria
• Fermentation:
  
  • End product: Volatile fatty acids
  • Some microbes deaminate amino acids → producing fatty acids
  • Some microbes produces urease by hydrolyzing carbamine, and releases NH₃^-

Question 8

Absorption of carbohydrates

Fructose

Answer 8

• Facilitated by GLUT-5 transporter
  
  • No energy is needed
  • GLUT-5 transporter are found on the luminal membrane and the basolateral membrane
  • Transport until the concentration is equal on both sides of the membrane

Question 9

Absorption of carbohydrates

Glucose / galactose

Answer 9

• Secondary transport mechanism
• Luminal receptor take up glucose /galactose only if Na⁺ binds before
  
  • Molecules binds → conformational change → turns into IC space
• Glucose / galactose and Na⁺ diffuses into the cytoplasm
  
  • Glucose / galactose is taken up by GLUT-2 transporter
  • Transported to basal membrane
  • Enters interstitium by facilitated transport

Question 10

Absorption of carbohydrates

Absorption from runinant stomach

Answer 10

• Volatile fatty acids
  
  • End product of carbohydrate fermentation
  • Decreased pH in rumen = increased absorption of VFAs
    
    • To maintain optimal pH in rumen
• Lactic acid
  
  • Product of easily digestible carbohydrates (grains)
  • Usually low concentration in rumen, but a sudden increase can cause acidosis
• Ammonia
  
  • Released from fermentative digestion of urea and protein
    
    • Absorbed in rumen
  • Ammonia goes to liver via v. porta
    
    • Urea is synthesized from ammonia
  • Low pH = decreased ammonia absorption
  • High pH = significant absorption (toxic)

Question 11

Carbohydrate digestion in small intestine, figure

Answer 11