Regulation of Blood Glucose Concentration (chapter 3 of hormonal communication)

Question 1

What two hormones act to keep blood glucose concentration constant?

Answer 1

Glucagon and insulin

Question 2

How does diet increase blood glucose concentration

Answer 2

1. Carbohydrate-rich food and sugary foods (which contain high levels of sucrose) are eaten
2. Carbohydrates are broken down in the digestive system to release glucose
3. Glucose is released and absorbed into the bloodstream
4. Blood glucose concentration rises

Question 3

How does glycogenolysis increase blood glucose concentration?

Answer 3

1. Glycogen stored in the liver and muscle cells is broken down into glucose
2. This is released into the bloodstream
3. Blood glucose concentration increases

Question 4

How does gluconeogenesis increase blood glucose concentration?

Answer 4

1. The production of glucose from non-carbohydrate sources - the liver is able to make glucose from glycerol (lipids) and amino acids
2. This glucose is released into the bloodstream
3. Blood glucose concentration increases

Question 5

How does respiration decrease blood glucose concentration

Answer 5

1. Some of the glucose in the blood is used by cells to release energy - required to perform normal body functions
2. During exercise - more glucose required as the body needs to generate more energy in order for muscle cells to contract
3. Higher level of physical activity = higher demand for glucose - so, blood glucose concentration decreases

Question 6

How does glycogenesis decrease blood glucose concentration

Answer 6

1. Blood glucose concentration level is too high
2. Glucose is converted to glycogen and stored in the liver
3. Blood glucose concentration decreases

Question 7

Role of insulin

Answer 7

• Produced by beta cells of the islets of Langerhans (pancreas)
• If blood glucose concentration is too high, the beta cells detect the rise and respond by secreting insulin into the bloodstream (and vice-versa = negative feedback)
• When insulin binds to its glycoprotein receptor, it causes a change in the tertiary structure of the glucose transport channels - channels open, which allows more glucose to enter the cell
• Insulin activates enzymes within some cells to convert glucose to glycogen and fat
• Broken down by enzymes in the cells of the liver
• It has to be constantly secreted to maintain its effect

Question 8

How does insulin lower blood glucose concentration?

Answer 8

1. It increases the rate of absorption of glucose by cells, in particular skeletal muscle cells
2. It increases the respiratory rate of cells - increases their need for glucose and causes a higher uptake of glucose from the blood
3. Increasing the rate of glycogenesis - insulin stimulates the liver to remove glucose from the blood by turning the glucose into glycogen and storing it in the liver and muscle cells
4. Increasing rate of glucose to fat conversion
5. Inhibiting the release of glucagon from the alpha cells of the islets of Langerhans

Question 9

Role of glucagon

Answer 9

• Produced by alpha cells of the islets of Langerhans (pancreas)
• if blood glucose concentration is too low - alpha cells detect this fall and respond by secreting glucagon into the bloodstream (and vise-versa = negative feedback)
• The only cells in the body that have glucagon receptors are the liver and fat cells

Question 10

How does glucagon raise blood glucose concentration?

Answer 10

1. Glycogenolysis - the liver breaks down its glycogen store into glucose and releases it back into the bloodstream
2. Reducing the amount of glucose absorbed by the liver cells
3. Increasing gluconeogenesis - increasing the conversion of amino acids and glycerol into glucose in the liver

Question 11

Control of insulin secretion

Answer 11

1. At normal blood concentration levels, potassium channels in the plasma membrane of beta cells are open and potassium ions diffuse out of the cell. The inside of the cell is at a potential of -70mV with respect to the outside of the cell
2. When blood glucose concentration rises, glucose enters the cell by a glucose transporter
3. The glucose is metabolised inside the mitochondria, resulting in the production of ATP
4. The ATP binds to potassium channels and causes them to close. They are known as ATP-sensitive potassium channels
5. As potassium ions can no longer diffuse out of the cell, the potential difference reduces to around -30mV and depolarisation occurs
6. Depolarisation causes the voltage-gated calcium channels to open
7. Calcium ions enter the cell and cause secretory vesicles to release the insulin they contain by exocytosis