Session 6 (2) - Metabolic pathways and their control

Question 1

Why is glucose preferred fuel in body?

Answer 1

Some tissues, such as CNS, have absolute glucose requirement

Question 2

How much glucose is present in body fluids, and how long can it support glucose dependent tissues for?

Answer 2

12g

Capable of supporting for 2 hours

Question 3

How is glucose stored?

Answer 3

As glycogen 300g in muscle, 100g in liver

Question 4

When are fatty acids converted to ketones?

Answer 4

When glucose is low during starvation.

Question 5

What cells cannot use fatty acids as fuel?

Answer 5

RBC’s and CNS

Question 6

How can amino acids be used by the body for fuel?

Answer 6

conversion to glucose and ketone bodies or by direct oxidation.

Question 7

How is blood glucose concentration controlled?

Answer 7

via the endocrine system by regulating the rates of entry of glucose into the blood and removal from it.

Question 8

What is hypoglycaemia? What are the acute effects?

Answer 8

When blood glucose <3.0mM
Trembling - Weakness - Tiredness - Headache
- Sweating - Sickness - Tingling around the lips
- Palpitations - Changes in mood - Slurred speech - Staggering walk

UNCONSCIOUSNESS AND DEATH

Question 9

What is hyperglycmaeia?

Answer 9

When blood glucose >7.0mM

Question 10

What sytems are effected by hyperglycaemia?

Answer 10

nervous, cardiovascular and renal systems

Question 11

What are two symptoms of hyperglycaemia?

Answer 11

Polyuria + polydipsia, caused by osmotic effects glucose

Question 12

Give effects of insulin (4) (Anabolic)

Answer 12

Increases glucose uptake and utilisation by muscle and adipose tissue

Promotes storage of glucose as glycogen in the liver and muscle

Promotes lipogenesis and storage of fatty acids as triacylglycerols in adipose tissues

Promotes amino acid uptake and protein synthesis in liver and muscle

Question 13

Give effects of Glucagon (3) (Catabolic)

Answer 13

Gluconeogenesis to maintain supplies of glucose for the brain
Glycogenolysis in the liver to maintain blood glucose for glucose-dependant tissues e.g. Brain
Lipolysis in adipose tissue to provide fatty acids for use by tissues

Question 14

What is the metablic effect of feeding?

Answer 14

The absorption of glucose, amino acids and lipids from the gut raises their blood concentration. The increases stimulate the endocrine pancreas to release insulin.

Question 15

What is the metabolic effect of fasting?

Answer 15

As blood glucose levels falls insulin secretion is depressed. This reduces the uptake of glucose by adipose tissue and muscle. The falling blood glucose concentration also stimulates glucagon secretion i.e. decreased insulin/anti-insulin ratio.

Question 16

On a page, write out contrasting features of insulin and glucagon

Answer 16

Insulin anabolic
Glucagon catabolic

Promotes storage of glucose as glycogen in the liver and muscle
Glycogenolysis in the liver to maintain blood glucose for glucose-dependant tissues e.g. Brain

Promotes lipogenesis and storage of fatty acids as triacylglycerols in adipose tissues
Lipolysis in adipose tissue to provide fatty acids for use by tissues

Promotes amino acid uptake and protein synthesis in liver and muscle
Gluconeogenesis to maintain supplies of glucose for the brain

Increases glucose uptake and utilisation by muscle and adipose tissue

Question 17

STARVATION

What occurs?

Answer 17

1)

• Glucagon stimulates breakdown of glycogen
• After run out, cortisol and glucagon stimulate gluconeogenesis
• Activities of both hormones increase

2)
- Lipolysis occurs at high rate due to decreased inuslin
- Fatty acids B oxidation. Cortisol prevents most cells from using glucose.
- Glycerol enters gluconeogenesis

3)

• Decreased insulin, ketone bodies produced which replaces glucose as fuel in brain
• spares protein by decreasing need for gluconeogenesis
• Ketosis occurs after extended period of time

4) Reduction in urea synthesis leads to decrease in amount and activity of enzymes involved in process. Refeeding syndrome can occur.