Lecture 6 (Part 1) Flashcards
Can Glucose, galactose, and fructose freely cross the enterocyte membrane
Glucose, galactose, and fructose are monosaccharides that cannot cross the enterocyte membrane freely through simple diffusion
what facilitates the transport of these sugars into the enterocytes hydrophobic lipid bilayer
3 different transporters:
- SGLT1 (Sodium dependent glucose transporter 1)
2 . GLUT2 - GLUT5
SGLT1 (Sodium-glucose linked transporter 1) function/how it works:
exit strategy of monosaccharides:
primary transporter for glucose and galactose
presence of sodium activates this transporter(SGLT1) which allows glucose and galactose to enter the cytoplasm of the enterocyte
Once inside the enterocyte, glucose and galactose can exit into the bloodstream through facilitated diffusion via glucose transporters (GLUT2) on the basolateral side of the cell.
GLUT2 Function:
Location:
affinity for glucose and galactose:
helps to transport glucose and galactose into the enterocyte
in the apical membrane
Has high affinity for glucose and galactose
GLUT5 function:
Location:
Exit strategy of monosaccharide:
Transport fructose into enterocyte
apical membrane
fructose exits into the bloodstream through GLUT2 transporters on the basolateral membrane
where does glucose, galactose, and fructose exit from the blood
*from the blood, these molecules enter the portal vein to the liver
blood stream –> portal vein –> liver
In the bloodstream Glucose is in its final state, however what is the issue with galactose and fructose
galactose and fructose still have to be converted
into glucose
*The liver holds some glucose and uses it for its own energy, but some glucose escapes the liver (liver released a controlled amount), which goes to the brain, as well as the pancreas. True or False
true
How does glucose enter the pancreas after escaping from the liver
Has GLUT2 transporters to allow glucose molecules to enter the organ
what reaction/negative feedbackloop occurs when glucose enters the pancreas
The pancreatic beta cells sense this rise in glucose, and in turn produces insulin
Insulin goes into the portal vein and drains towards the liver (the liver is the first area to see insulin)
The insulin binds to the receptors on the surface of the liver cells and tells the liver to store a large amount of glucose as glycogen which reduces the
amount of glucose circulating
↑ glucose in pancreas → insulin release by pancreas → insulin through portal vein →attaches to liver receptors → tells liver to store glucose as glycogen → reduce glucose circulation
How does glucose enter skeletal muscle as a result of insulin?
↑ blood glucose levels rise –>
pancreas releases insulin –>
insulin bind to receptor on skeletal muscle –>
translocation of GLUT4 to cell membrane–>
glucose enter cell
role of glucose in skeletal muscle
energy
storage as glycogen
the role of insulin in adipocytes (adipose tissue) :
↑ blood glucose levels rise –>
pancreas releases insulin –>
Insulin also goes to adipocytes in the subcutaneous area –>
insulin bind to receptor on adipose tissue –>
translocation of GLUT4 to cell membrane–>
glucose enter cell
difference between adipocytes (adipose tissue) and skeletal muscle in terms of glycogen
stores very little glycogen, unlike skeletal muscle.
takes glucose and converts it into Gly-3P
Gly-3P merges with 3FA to form triglycerides
How is glucose transported inside the brain
via GLUT1 and GLUT3.
where is GLUT1 located
GLUT1 (located in the blood-brain barrier)
where is GLUT3 located
GLUT3 (found in neurons)
Function of GLUT1
GLUT1 ensures a continuous supply of glucose from the bloodstream to the brain
Function of GLUT3
GLUT3 is highly efficient in transporting glucose into neurons
is glucose uptake in the brain Insulin-Independent
Unlike peripheral tissues such as skeletal muscle and adipose tissue, the brain does not rely on insulin for glucose uptake
Are GLUT1 and GLUT3 always present on the cell membrane
GLUT1 and GLUT3 always present on the cell membrane which allow constant flow of glucose into the cells;
GLUT3 and GLUT1 are characterized by
GLUT3 and GLUT1 are characterized by high affinity for glucose, meaning they are saturated with substrate (glucose) even at normal blood glucose levels
Do wide variations in blood glucose levels cause little or large change in the rate at which glucose is taken up by the brain
Wide variations in blood glucose levels cause little change in the rate at which glucose is taken up by the brain due to the high affinity of GLUT1 and GLUT3 for glucose
It’s only when blood glucose falls below a critical threshold (around 2 mmol/L) that mental function can be impaired
This emphasizes the brain’s reliance on a steady supply of glucose for optimal function.
