Regulation Of Blood Glucose Concentration.

What is blood glucose concentration kept constant by?

The action of insulin and glucagon.

What can blood glucose increase as a result of?

• Diet.

• Glycogenolysis.

• Gluconeogenesis.

How can diet increase blood glucose concentration?

When you eat carbohydrate-rich foods, the carbohydrates they contain are broken down into the digestive system to release glucose. The glucose released is absorbed into the bloodstream, increasing blood glucose.

How does glycogenolysis increase blood glucose concentration?

Glycogen stored in the liver and fat cells is broken down into glucose which is glucose concentration.

How does gluconeogenesis increase blood glucose concentration?

After the production of glucose from non-carbohydrate sources, the glucose is released into the bloodstream causing an increase in blood glucose concentration.

How can blood glucose be decreased?

• Respiration.

• Glycogenesis.

How does respiration decrease blood glucose concentration?

Some of the glucose in the blood is used by cells to release energy. During exercise, more glucose is needed by the body to generate more energy for muscles to contract.

How does glycogenesis decrease blood glucose concentration?

When blood glucose is too high, excess glucose taken in through the diet is converted into glycogen, which is stored in the liver.

What is insulin produced by?

The beta cells of the islet of Langerhans.

What happens if blood glucose is too high?

This is detected by the beta cells of the islet of Langerhans, which respond by secreting insulin directly into the bloostream.

Which cells have insulin receptors on their cell surface?

Virtually all body cells.

What happens when insulin binds to its glycoprotein receptor?

It causes a change in the tertiary structure of the glucose transport protein channels, causing the channels to open, allowing more glucose to enter the cell. Insulin also activates enzymes that convert glucose into glycogen and fat.

How does insulin lower the blood glucose concentration?

By:

• increasing the rate of absorption of glucose by cells, in particular skeletal muscle cells

• increasing the respiratory rate of cells - this increases their need for glucose and causes a higher uptake of glucose from the blood

• 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

• increasing the rate of glucose to fat conversion

• inhibiting the release of glucagon from the a cells of the islets of Langerhans.

What is insulin broken down by?

Enzymes in the cell of the liver. Therefore, to maintain its effect, it has to be constantly secreted.

Following a rise in glucose concentration, when it returns to normal, what is this detected by?

The beta cells of the pancreas, and when it falls below a set level, the beta cells reduce their secretion of insulin - negative feedback.

What is glucagon produced by?

The alpha cells of the islets of Langerhans in the pancreas.

What happens if the blood glucose concentration is too low?

This is detected by alpha cells which respond by secreting glucagon directly into the bloodstream.

Which cells have glucagon receptors?

Only liver and fat cells - therefore these are the only cells that can respond to glucagon.

How does glucagon raise blood glucose concentration?

By:

• glycogenolysis - the liver breaks down its glycogen store into glucose and releases it back into the bloodstream reducing the amount of glucose absorbed by the liver cells

• increasing gluconeogenesis - increasing the conversion of amino acids and glycerol into glucose in the liver.

Following an increase, what happens when blood glucose concentration returns to normal?

This is detected by alpha cells. When it rises above a set level, the alpha cells reduce their secretion of glucagon (negative feedback).

Is blood glucose concentration constant?

No, but it fluctuates around a set point as the result of negative feedback.

At normal blood glucose levels, are potassium channels in the plasma membrane of beta cells open or closed?

Open, allowing potassium ions to diffuse out of the cell. The inside of the cell has a potential of -70mV.

What happens in the beta cells when blood glucose concentration rises?

Glucose enters the cell by a glucose transporter.

What happens to the glucose inside the beta cell?

It is metabolised inside the mitochondria, resulting in the production of ATP.

What does the ATP from the metabolising of glucose do?

It binds to ATP-sensitive potassium channels and causes them to close.

What happens following the closing of the ATP-sensitive potassium channels?

Potassium ions are no longer able to diffuse out of the cell, reducing the potential difference to around -30mV and depolarisation occurs.W

What does the depolarisation of the beta call cause?

It causes the voltage-gated calcium channels to open and an influx of calcium ions.

What happens to the beta cell following the influx of calcium ions?

Secretory vesicles release the insulin they contain by exocytosis.