14.3- Regulation Of Blood Glucose Concentration

Question 1

How can blood glucose concentration be increased?

Answer 1

1. Diet (eating carbohydrates etc)
2. Glycogenolysis.
3. Gluconeogenesis

Question 2

Glycogenolysis

Answer 2

Glycogen stored in the liver and muscle cells is broken down into glucose which is released into the bloodstream
Glucose concentration rises

Question 3

Gluconeogenesis

Answer 3

The production of glucose from non-carbohydrate sources.

Eg. Liver can produce glucose from glycerol and amino acids

Question 4

How can blood glucose concentration be decreased?

Answer 4

1. Respiration.

2. Glucogenesis

Question 5

Glucogenesis

Answer 5

Excess glucose taken in from the diet is converted into glycogen which is stored in the liver.

Question 6

What is the role of insulin?

Answer 6

• if blood glucose concentration is too high b-cells detect this and respond by secreting insulin directly into the bloodstream.

Question 7

How does insulin work?

Answer 7

• all body cells (except rbc) have insulin receptors on their cell membrane.
• when insulin binds to its glycoprotein receptor, it causes a change in the tertiary structure of the glucose transport protein channels.
• this causes the channels to open allowing more glucose to enter the cell.
• insulin also activates enzymes in some cells to convert glucose to glycogen and fat.
• works in negative feedback cycle.

Question 8

How does insulin lower blood glucose concentration?

Answer 8

1. Increasing rate of glucose absorption by cells, especially skeletal muscle cells.
2. Increasing rate of respiration in cells - increases glucose uptake.
3. Increasing rate of glycogenesis.
4. Increasing rate of glucose conversion to fat.
5. Inhibiting release of glucagon from a-cells of the islets of Langerhans.

Question 9

Why does insulin need to be constantly secreted?

Answer 9

It is broken down by enzymes in the cells of the liver.
- depending on the food eaten, insulin secretion can begin within minutes of the food entering the body and continue for several hours.

Question 10

Role of glucagon.

Answer 10

• if blood glucose concentration is too low, the a-cells detect this and respond by secreting glucagon directly into the bloodstream.
  Only liver and fat cells have glucagon receptors and therefore only they can respond to glucagon.
• works in negative feedback cycle.

Question 11

How does glucagon raise blood glucose concentration?

Answer 11

1. Glycogenolysis.
2. Reducing amount of glucose absorbed by liver cells.
3. Increasing gluconeogenesis.

Question 12

Interaction of insulin and glucagon?

Answer 12

(Textbook diagram)

• insulin and glucagon are antagonistic hormones meaning they work against each other.
• the system of maintaining blood-glucose concentration is said to be self-regulating.
• blood glucose is not constant, but fluctuates around a set point as a result of negative feedback.

Question 13

Mechanism of insulin secretion.

Answer 13

(Textbook diagram)

1. At normal bgc, potassium channels in plasma membrane of b-cells are open. K+ ions diffuse out of cell.
2. When bgc rises, glucose enters cell by a glucose transporter.
3. The glucose is metabolised inside the mitochondria= ATP production.
4. ATP binds to potassium channels and causes them to close. Known as ATP sensitive potassium channels.
5. K+ ions can no longer diffuse out of cell. Potential difference reduces and depolarisation occurs.
6. This causes voltage-gates calcium channels to open.
7. Calcium ions enter cell and cause secretory vesicles to release the insulin they contain via exocytosis.