Metabolism Part 2

Question 1

What are signals that stimulate insulin secretion?

Answer 1

high levels of plasma glucose, and high levels of plasma amino acids

Question 2

What are signals that stimulate glucagon secretion?

Answer 2

low level of plasma glucose, high level of plasma amino acids

Question 3

Why do amino acids trigger the secretion of both insulin and glucagon?

Answer 3

because high amino acids can mean that you just had a meal-> insulin;
or you could be low in glucose and high in amino acids relatively and have to go through gluconeogenesis -> glucagon

Question 4

What stimulates insulin secretion by beta cells?

Answer 4

parasympathetic output, peptides (GLP-1,GIP), high plasma glucose, high plasma amino acids

Question 5

What inhibits alpha cells from secreting glucagon?

Answer 5

increased plasma glucose

Question 6

Why are there so many regulatory pathways?

Answer 6

preventing hyperglycemia- we do not want glucose secretion to go over board (happening before the food is digested and absorbed)

Question 7

Why are we looking at functions of glucose transporters in resting skeletal muscle?

Answer 7

Because when we exercise, we express more GLUT-4 transporters into the cell membrane, which lowers glucose level because you take in extra glucose

Question 8

Insulin’s effect on glucose transporters occurs in what body structures?

Answer 8

adipose tissue, resting skeletal muscle, and hepatocytes

Question 9

In the absence of insulin, (glucose transporter; adipose tissue and resting skeletal muscle)

Answer 9

glucose cannot enter the cell; the transport is not expressed on the cell surface, transporter is in the vesicle (cell cannot take advantage of the glucose)

Question 10

In the presence of insulin (in glucose transporters of adipose tissue and resting skeletal muscle)

Answer 10

the paracrine receptor that insulin binds to causes phosphorylation which causes exocytosis of the transporter out of the vesicle and GLUT-4 is expressed on the membrane; glucose is able to go through GLUT-4 to come into the cell

Question 11

What is the function of GLUT-4

Answer 11

insulin-stimulated glucose uptake

Question 12

The functions of the GLUT-4 transporter in the adipose tissue and resting skeletal muscle is what kind of effect from insulin?

Answer 12

direct

Question 13

The functions of the GLUT-2 in hepatocytes is what kind of effect by insulin?

Answer 13

indirect

Question 14

What kind of transport does GLUT2 do?

Answer 14

facilitated diffusion- driven by concentration gradient

Question 15

when a hepatocyte is in a fed state what is occurring

Answer 15

insulin activates hexokinase which maintains the glucose gradients

Question 16

How does hexokinase maintain the glucose gradient

Answer 16

glucose uses the gradient to come into the cell, hexokinase then phosphorylates that glucose to make glucose-6-phosphate, and since glucose-6-phosphate is a different molecule than glucose, GLUT-2 cannot transport it out of the cell and it also lowers the glucose concentration since it is not the same form of glucose

Question 17

hepatocyte in fasted state

Answer 17

the glucose gradient favors glucose to leave the cell; since the cell does not have hexokinase, it activates enzymes that breakdown glycogen and make glucose-6-phosphate in the liver, so now intracellular glucose levels are high and glucose can use GLUT-2 to leave

Question 18

Hexokinase

Answer 18

an enzyme that adds a phosphate group to glucose to make glucose-6-phosphate

Question 19

Can GLUT-2 transport glucose-6-phosphate?

Answer 19

no! only glucose; this is what leads to glucose trapping