Glucose Homeostasis

Question 1

Why is glucose homeostasis important

Answer 1

Glucose is the only fuel used by the brain under starvation conditions and the only fuel RBC can use at all

Question 2

What is hyperglycaemia

Answer 2

Too high concentration of glucose associated with micro vascular damage and protein cross linking in the long term

Question 3

What is hypoglycaemia

Answer 3

Too low concentration of glucose associated with immediate fatigue, confusion, loss of consciousness, seizures etc.

Question 4

What are the three main types of hypoglycaemia

Answer 4

Insulin induced, post prandial (after a meal) and fasting (including alcohol related fasting)

Question 5

Why can glucose not be stored as it is

Answer 5

Soluble (osmotic problems)

Question 6

What is the function of glycogen in glucose homeostasis

Answer 6

Serves as a buffer to maintain serum glucose levels

Question 7

What are the two major glycogen storage sites

Answer 7

Liver (10% by weight) and skeletal muscle (2% by weight)

Question 8

Which organs are sensitive to low glucose

Answer 8

Brain and pancreas

Question 9

Which organ is sensitive to high glucose

Answer 9

Pancreas

Question 10

What are the major hormones in glucose homeostasis

Answer 10

Insulin and glucagon

Question 11

What are the minor hormones in glucose homeostasis

Answer 11

Epinephrine, norepinephrine and cortisol

Question 12

How do epinephrine/norepinephrine and cortisol affect serum glucose

Answer 12

Raises it

Question 13

What is insulin

Answer 13

51 AA polypeptide hormone produced in beta cells of islets of lamgerhans in pancreas that

Question 14

How is insulin secreted regulated

Answer 14

Regulated by increased uptake of glucose (GLUT2), amino acids ans GI hormones and decreased secretion of epinephrine (stress/exercise)

Question 15

What are the effects of insulin

Answer 15

Carbohydrate metabolism (increased uptake via GLUT4, glycogenosis and decreased gluconeogenesis)
Lipid metabolism (reduced FA release and break down of fat, more fat produced for storage)

Question 16

How does insulin work

Answer 16

By increasing expression of GLUT4 and induces a signalling cascade that activates glycogen synthase and inhibits glycogen phosphorylase (hydrolysis enzyme), promotes fat synthesis and inhibits fat breakdown (lipolysis)

Question 17

What is GLUT4

Answer 17

Insulin responsive glucose transporter

Question 18

How does insulin affect gene expression

Answer 18

Activates glucokinase and leptin and inhibits genes related to gluconeogenesis and glucose 6-phosphatase

Question 19

What metabolic pathways does insulin increase

Answer 19

Glycolysis,glycogenesis , lipogenesis

Question 20

What metabolic pathways does insulin decrease

Answer 20

Gluconeogenesis, glycogenolysis and lipolysis

Question 21

What is glucagon

Answer 21

Hormones secreted by alpha cells of islets in pancreas that opposes insulin action

Question 22

What stimulates glucagon release

Answer 22

Low blood glucose, amino acids and epinephrine

Question 23

What inhibits glucagon release

Answer 23

High blood glucose and insulin producing beta cells

Question 24

Why does amino acids stimulate both insulin and glucagon release

Answer 24

After a protein rich meal there is a danger of hypoglycaemia due to insulin release so glucagon is also required to overcomes this

Question 25

What is the action of glucagon

Answer 25

Glycogenolysis and increase use of amino acids as precursors for gluconeogenesis and inhibition of lipogenesis (mainly in liver)

Question 26

Why can only the liver glycogen store maintain glucose levels

Answer 26

Skeletal muscle store does not respond to glucagon and does not contribute to serum glucose homeostasis as synthesises glycogen at rest and degrades it during exercise

Question 27

What is the function of glycogen synthase

Answer 27

Synthesis of glycogen

Question 28

What is the function of glycogen phosphorylase

Answer 28

Degradation of glycogen

Question 29

How does the liver respond to high glucose

Answer 29

Increases glucose uptake, glycolysis and lipogenesis and glycogenesis

Question 30

Describe the role of glucose kinase when glucose levels of are high

Answer 30

Traps glucose as glucose 6-phosphate to quickly decrease intracellular glucose

Question 31

How does the liver respond to decreased serum glucose

Answer 31

Reduced glucose uptake, lipogenesis and glycogenesis and increased glycogenolysis and gluconeogenesis

Question 32

Why is the liver important for glucose homeostasis

Answer 32

Only liver (and kidney) express glucose 6-phosphate by kidney cannot correct hypoglycaemia and muscle glycogen cannot be used to replace serum glucose homeostasis

Question 33

What is liver damage characterised by

Answer 33

Hypoglycaemia

Question 34

Why is the liver glycogen a short term glucose source

Answer 34

Hours not days supply so regular meals are required to replenish stores

Question 35

How does type 1 diabetes lead to hypoglycaemia

Answer 35

Cannot produce insulin, so no glycogen stores in liver, so liver cannot regulate serum glucose homeostasis

Question 36

What is gluconeogenesis

Answer 36

Metabolic process used to replenish glucose when glycogen is depleted by protein breakdown and processing of amino acids as a carbon source (or lactate and glycerol)

Question 37

What cannot be used as a carbon source for gluconeogenesis

Answer 37

Fatty acids

Question 38

How do we replenish glucose in the fed stare

Answer 38

Dietary glucose

Question 39

How do we replenish glucose in the fasting state

Answer 39

Breakdown of live glycogen and gluconeogenesis

Question 40

How can alcohol induce hypoglycaemia

Answer 40

Alcohol inhibits gluconeogenesis