Topic A9

Question 1

Blood sugar levels and its regulation

Define blood sugar

Question 2

Blood sugar level and its regulation

Give the special case of ungulates

Answer 2

• Normally the blood glucose concentration does not differ significantly from the concentration of the monosaccharides, except from ungulates in foetal ages
• • The placenta of most ungulates produces fructose​, consequently the fetal ungulates have high blood concentration of fructose (instead of glucose​)

Question 3

Blood sugar level and its regulation

Physological values of blood sugar level

Answer 3

• Normal range of blood glucose level:
  
  • Monogastric mammals: 4-5 mmol/l
  • Ruminants: 2-3 mmol/l
  • Birds: 8-9 mmol/l

Question 4

Blood sugar level and its regulation

Hormonal regulation of blood sugar level

Answer 4

• The blood glucose level is controlled primarly by the action of the liver, which takes up or release large amounts of glucose in response to hormonal signals​
• Insulin:
  • ​The only hormone which reduces the blood glucose level
  • It promotes the entry of glucose and some other sugars into msucle and fat cells → decreased glucose level (hypoglycemic effect)

Question 5

Blood sugar level and its regulation

Intracellular regulatory mechanisms

Answer 5

• The precusor of blood gluces is glucose-6-P
• Glucose-6-P-phosphatase
  
  • The formation of free glucose is brough about by this enzyme
  • Catalyzes the hydrolytic reaction:
    
    • Glucose-6-P + H₂O → glucose + Pⁱⁿ
  • The enzyme is found in:
    
    • Endoplasmic reticulum of the liver
    • Kidney to a small extent
  • The enzyme is not present in other tissues
    
    • Eg. in muscles or in the brain, the tissues have no capacity to donate free glucose to the blood

Question 6

Blood sugar level and its regulation

Signaling pathways

Answer 6

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Question 7

Blood sugar level and its regulation

Transporters of glucose circulation

Answer 7

• GLUT-1
  
  • ​Blood (erythrocytes)
  • Brain
• GLUT-2
  
  • ​Liver
  • Kidney
  • Intestine
• GLUT-3
  
  • ​Brain
• GLUT-4
  
  • ​Adipose tissue
  • Muscle
• GLUT-4 is insulin sensitive
  
  • Insulin binding to insulin receptor induces a signal transduction cascade that allows GLUT-4 to transport glucose into the cell