Blood glucose level, diabetes, fructose/galactose (PPP not incl.) Flashcards
What are blood glucose ranges
- in postabsorptive state
- after carbohydrate meal
- during starvation
- postabsorptive phase: 4.5 - 5.5 mmol/L
- after carbs: 6.5 - 7.2 mmol/L
- starvation: 3.3 - 3.9 mmol/L
lower glucose level possible if hypoglycemia develops slowly
Describe the Cori cycle.
- glycolysis in mm. produces pyruvate
- pyruvate converted to lactate
- lactate exported into blood stream
- lactate taken up by liver
- incorporated into gluconeogenesis
- glucose exported into blood stream
- glucose taken up by mm.
What are the effects of hyperglycemia in the liver?
- incr. glucose uptake by GLUT 2
- glucokinase activated due to high [glucose]
- incr. glycogenesis due to activation of PP1 → enhanced glycogen synthase activity
- decr. glycogenolysis due to glucose sensory function of glycogen phosphorylase
- active PDC incr. FA synthesis
What are the effects of hyperglycemia in the pancreas?
- incr. glucose uptake by GLUT 2
- glucokinase triggers insulin secretion from pancreatic β-cells
What are the effects of hyperglycemia in peripheral tissue (muscle, adipocytes)?
- incr. amount of GLUT 4 in membranes due to insulin
- incr. glycogenesis
- decr. glycogenolysis
- incr. glycolysis due to upregulation of PFK1
What are the long term effects of hyperglycemia?
insulin represses all enzymes involved in gluconeogenesis, esp. PEPCK → decr. gluconeogenesis
What are the effects of hypoglycemia in the liver?
incr. gluconeogenesis
What causes the incr. risk of hypoglycemia during pregnancy?
- limited ketogenesis in the fetus
- incr. glucose demand of the fetus, due to brain/body rate
- no gluconeogenesis bc PEPCK is repressed, no G6Pase
- glycogen storage is limited
Distinguish btw the types of diabetes mellitus.
- type I: insulin deficiency due to destruction of pancreatic β-cells
- type II: insulin resistance
What might be a long term effect of diabetes?
decr. amount of PEPCK due to long-term repression by insulin
What is glucoseuria?
more glucose secreted into renal tubules than can be reabsorbed (limited rate of 2 mmol/min)
→ exceeding renal threshold, hence excreted w/ urine
Which transporters are involved in galactose/fructose uptake in the intestine?
- galactose: actively pumped into cell by SGLT, then leaves entercoyte basolaterally via GLUT 2
- fructose: passive diffusion via GLUT 5 into cell, then leaves enterocyte basolaterally via GLUT 2, 5
Briefly describe the main steps of fructose metabolism in the liver and sperms.
- fructokinase: fructose + ATP → F1P + ADP
- aldolase B: F1P → DHAP + glyceraldehyde
- triosekinase: glyceraldehyde + ATP→ glyceraldehyde-3P + ADP
⇒ DHAP + glyceraldehyde-3P can be introduced for glycolysis or gluceneogenesis
How differs the fructose metabolism in per. tissue from the fructose metabolism in the liver?
no fructokinase, but hexokinase (can process glucose and fructose):
fructose + ATP → F6P + ADP
What is the difference btw glucose and fructose metabolism in the liver?
Why is it clinically important?
metabolism of fructose happens much faster b/c it bypasses the main regulatory step of glycolysis (PFK1) and also causes incr. activity of glucokinase
⇒ uncontrolled NADH + acetyl-CoA production leads to incr. TAG and cholesterol synthesis in the liver (fatty liver)
= risk factor of obesity + metabolic syndrome
Describe the polyol pathway.
Why is it important?
It is regulated by?
Which enzymes are involved?
important in sperms to provide E source, regulated by testosterone level
NOTE: NADPH/H+ used, NADH/H+ produced
How are glycoproteins produced from galactose?
Explain the steps of lactose synthesis in the lactating mammary gland.
- glucose transported into gland by GLUT 1/3
- hexokinase → G1P
- first 2 steps of glycogenesis: G1P → UDP-glucose
- 4-epimerase → UDP-galactose
-
lactose synthase
UPD-galactose + glucose → UDP + lactose
