Topic 6 - Hormonal Regulation of Glucose (Homeostasis and Eqilibrium)

Question 1

Learning objectives

Answer 1

1. Identify that blood sugar levels can be maintained by a negative feedback loop
2. Describe the mechanics that maintain blood sugar in the fed state
3. Describe the mechanics that maintain blood sugar during the fasting state

Question 2

Glucose

Answer 2

Main source of energy for the brain
- Not stored in sufficient high volumes in the brain
- Therefore it is crucial to circulate it in the blood

Approx. 5mmol is ‘normal’ level
- If drops below, can result in a coma

Question 3

Overveiw of bloog glucose

Answer 3

1. Glucose entres the body via diffusion after food is digested in the gut
2. Glucose entres blood stream and circulates until it entres a muscle tissue via diffusion again

• Liver stores glucose and releases it into bloodstream when levels start to drop
• Skeletal muscle and liver store glucose when levels are too high.

Question 4

Glucose transporters for diffusion

Answer 4

SGLT transporters:
- Sodium glucose coTransporters
- Uses Na+ to diffuse glucose across the membrane passively

GLUT 2&4 Transporters:
- Glucose Transporters
- Glucose flows across membrane passively

Question 5

SGLT Transporters

Answer 5

Found in the gut (Small Intestine) and kidney
- Used to transport glucose in urine back into the blood
- Is critical to move glucose around, but doesn’t control blood glucose.

Question 6

GLUT Transporters

Answer 6

GLUT 2 Transporters:
- In the Liver
- Works consistantly
- Critical for blood sugar regulation

GLUT 4 Transporters:
- In Skeletal Muscle and Fat
- Is a regulated transporter (Not constantly working)
- Insulin promotes amount of GLUT-4 Transporters working

Blood sugar must be regulated and cannot just rely on diffusion as optimal range will not be met

Question 7

Fed State

Answer 7

The body has consumed food and therefor the blood glucose levels increase
Glucose is then taken out of the blood stream and stored in skeletal muscle, fat and liver.

Question 8

Skeletal Muscle in Fed State

Answer 8

1. Glucose entres the muscle cell through GLUT-4 transporters with the use of insulin
2. Glucose is then converted into glycogen through metabolic pathways, lowering the glucose concentration in the muscle cell, therefore allowing diffusion to continue
3. Glycogen is then stored as energy

Question 9

Skeletal Muscle in Fasting state

Answer 9

1. The body has used most of the blood glucose in circulation Glycogen stores are used up in anareobic or aerobic pathways with glucagon.
2. Extreme fasting may lead to breakdown of skeletal muscle for amino acids as energy.

Question 10

Fat in Fed State

Answer 10

1. Fat cells take up glucose and fatty acids through GLUT-4 transporters via diffusion, converting them into triglycerides
2. The conversion of glucose into triglycerides lowers the concentration of glucose in the adipose cell, allowing for further diffusion of glucose.

Question 11

Fat in Fasting state

Answer 11

1. Triglycerides are broken down into fatty acids and glycerol, they are then released back into the blood stream, increasing the blood sugar levels.

Question 11

Liver in the Fed State

Answer 11

1. Glucose entres the liver through GLUT-2 transporters
2. Glucose undergoes metabolic pathways and is converted into glycogen
3. The conversion into glycogen allows for the diffusion of glucose into the liver due to concentration gradients
4. The liver is able to reversibly convert glycogen back into glucose when needed.

Question 12

Liver in the fasting state

Answer 12

1. Liver is triggered to create glucose from its glycogen stores
2. Glucose is then released into the blood stream through diffusion as there is a lower concentration gradient in the blood
   - The liver is the only organ that can readily do this.
3. Products of skeletal muscle and fat tissue are processed back into the liver before being pumped back into the blood stream
4. During regular fasting, glycerol, amino acids and lactate are used to create glucose through metabolic pathways with pyruvate

Question 13

Controlled storage of glucose

Answer 13

Insulin

Question 14

Insulin

Answer 14

• Primary Hormone in fed state
• Produced by beta cells in pancreas
• When blood glucose levels too high, tells muscle, fat and liver to take up and store glucose.
• Increases the amount of GLUT-4 transporters on cell membrane
• Targets the metabolic pathway in the liver to enhance glycogen stores

Question 15

Contolled release of glucose

Answer 15

Glucagon

Question 16

Glucagon

Answer 16

• Primary Hormone in fasting state
• When blood glucose levels are too low, glucagon is released by the alpha cells of the pancreas to tell the liver release glucose from its stores