The Feed-Fast Cycle: Role of Hormones

Question 1

What hormones are the main hormonal regulators of blood glucose levels?

Answer 1

Insulin
Glucagon
Epinephrine
Cortisol

Question 2

The _______buffers blood glucose levels. After a meal, it takes up large amounts of glucose and during fasting, it releases glucose into the blood. ________ is used in both processes.

Answer 2

Liver

GLUT-2

Question 3

The brain uses which glut transporter for he uptake of glucose?

Answer 3

GLUT-1

Question 4

What is postprandial?

Answer 4

The time of about 2-3 hours after a meal is referred to as postprandial

Question 5

In the postprandial phase, the dietary monosaccharides are taken up in large amounts into the __________ via the __________. The free glucose is ________by _________and the glycogen store is filled and ______is performed. Both pathways are favored by the high ________ ratio

Answer 5

Liver (Glut-2)
Portal Vein
phosphorylated
glucokinase
glycolysis
insulin/glucagon

Question 6

At very high glucose levels and extensive glycolysis, the liver synthesizes _______ and ________.

Answer 6

Fatty acids

Cholesterol

Question 7

The postabsorptive phase is about ____ hours after food intake.

Answer 7

5-7

Question 8

Blood glucose levels are ______ in the postabsorptive phase

Answer 8

decreased

Question 9

What is characteristic about the postabsorptive phase?

Answer 9

• high glucagon/insulin ratio
• liver releases glucose
• Insulin = low
• Epinephrine & Cortisol = elevated; leading to lypolysis

Question 10

What processes are favored by high glucagon/insulin ratio?

Answer 10

Glycogen degradation

Gluconeogenesis

Question 11

How do hepatocytes release free glucose into the blood?

Answer 11

GLUT-2

Question 12

The liver glycogen stores are empty after about______ and from then on, _________ will provide the blood glucose that is needed for the total body.

Answer 12

1 day

gluceneogensis

Question 13

How does ACTH released under stress situations affect Insulin?

Answer 13

Under stress situations, the pituitary gland releases ACTH which stimulates release of cortisol from the adrenal cortex

• Cortisol leads in the adrenal medulla to methylation of norepinephrine to epinephrine (PNMT, SAM) and release of both catecholamines into the blood
• Epinephrine inhibits insulin release from b-cells and stimulates glucagon release from a-cells

Question 14

Cortisol has no effect on ________ but stimulates _________

Answer 14

Glycogen breakdown

Gluconeogenesis

Question 15

Epinephrine/Norepinephrine stimulates _______ but has no effect on ________

Answer 15

Glycogen breakdown

Gluconeogenesis

Question 16

Glucagon stimulates both _____ and _____

Answer 16

Glycogen breakdown

Gluconeogensis

Question 17

Glucagon leads in the liver to ______ and to _____.

Answer 17

Degradation of fatty acids

Synthesis of ketone bodies

Question 18

Cortisol supports gluconeogensis by inducing what enzyme needed for long term gluconeogenesis?

Answer 18

PEP carboxykinase

Question 19

Insulin release is favored by glucose and what amino acids?

Answer 19

especially by Leucine (dietary essential)

also arginine

Question 20

Glucagon release is favored by epinephrine and what amino acids?

Answer 20

Especially alanine

also arginine

Question 21

Which amino acid leads to the release of both insulin and glucagon?

Answer 21

Arginine

Question 22

Gluconeogensis is only performed where?

Answer 22

Liver

Question 23

Ketogenesis is only performed where?

Answer 23

Liver

Question 24

High levels of glucose after a meal lead in the liver to? In fat cells to? In muscle to?

Answer 24

Liver: Glycolysis, glycogen synthesis, fatty acid and cholesterol synthesis

Fat cells: Glycolysis and TAG synthesis

Muscle: Glycolysis and glycogen synthesis

Question 25

High levels of blood fatty acids during fasting lead in the liver to? In the muscle to?

Answer 25

Liver: B-oxidation of FA and Ketogenesis

Muscle: B-oxidation

Question 26

Insulin induces key enzymes of irreversible steps of

Answer 26

Glycolysis
PPP
FA and cholesterol synthesis

Question 27

Glucagon induces key enzyme of irreversible steps of

Answer 27

Gluconeogenesis

Question 28

What are the key regulated enzymes of lipid metabolism in the liver (the enzymes are induced by insulin)

Answer 28

FA (de novo) synthesis:

• Acetyl CoA Carboxylase
• FA synthase complex

Cholesterol synthesis:
-HMG CoA reductase

Question 29

What are the key regulated enzymes of lipid metabolism in fat cells?

Answer 29

TAG Degradation:

- Hormone-sensitive lipase (inactive at insulin ruling; need P for activation)

Question 30

Fat cells after a meal: high insulin blood levels mobilize ______ in fat cells and activates ______ in capillaries.

Answer 30

GLUT-4

Lipoprotein Lipase

Question 31

Why is the blood glucose level critical and well regulated?

Answer 31

Blood glucose is the primary fuel for the brain in the well-fed state and also during the first days of fasting. Glucose is also all the time the only fuel for RBC and other cells without mitochondria

Question 32

Which key regulatory enzymes of glycolysis and the PPP are active in the liver at high serum insulin/glucagon ratio?

Answer 32

Insulin induces the key regulatory enzymes of liver glycolysis and the PPP: glucokinase, PFK-1, the bifunctional enzyme, pyruvate kinase and glucose 6-P dehydrogenase.

The PFK-2 activity of the bifunctional enzyme and pyruvate kinase are dephosphorylated and active. The PPP is active as the demand for NADPH is increased during synthesis of fatty acids and cholesterol.

Question 33

How is it regulated that glycolysis and not gluconeogenesis takes place in liver at high insulin/ratio?

Answer 33

At insulin/glucagon ratio, the bifunctional enzyme forms fructose 2,6-bisphosphate which has two allosteric actions: a.) it activates PFK-1 ( which is the key regulated enzyme of glycolysis) and b.) at the same time, other molecules of fructose 2,6-bisphosphate inhibit fructose 1,6-bisphosphatase (the key regulated enzyme of gluconeogenesis) in the liver

Question 34

How is it regulated that glycogen synthesis and not glycogen degradation takes place in the liver at high insulin/glucagon ratio?

Answer 34

Insulin leads to the active (dephosphorylated) glycogen synthase.

Insulin leads to the inactive (dephosphorylated) glycogen phosphorylase kinase which results in the inactive (dephosphorylated) glycogen phosphorylase