chapter 14 p3

Question 1

Role of glucagon:

Answer 1

Glucagon is produced by the a cells of the islets of Langerhans in the pancreas.
If the blood glucose concentration is too low, the a cells detect this fall in blood glucose concentration and respond by secreting glucagon directly into the bloodstream.
Unlike insulin, the only cells in the body which have glucagon receptors are the liver cells and fat cells - therefore these are the only cells that can respond to glucagon.

Question 2

Glucagon raises blood glucose concentration by:

Answer 2

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.

Question 3

Glucagon feedback

Answer 3

As blood glucose concentration returns to normal, this is detected by the a cells of the pancreas.
When it rises above a set level, the a cells reduce their secretion of glucagon. This is another example of negative feedback.
The feedback causes the corrective measures to be switched off, returning the system to its original (normal) level.

Question 4

negative feedback diagram

Answer 4

Question 5

Interaction of insulin and glucagon
p1

Answer 5

insulin and glucagon work together to maintain a constant blood glucose concentration.
Insulin and glucagon are antagonistic hormones, that is, they work against each other.
The system of maintaining blood glucose concentration is said to be self-regulating, as it is the level of glucose in the blood that determines the quantity of insulin and glucagon that is released.

Question 6

Interaction of insulin and glucagon
p2

Answer 6

Blood glucose concentration is not constant, but fluctuates around a set point as the result of negative feedback.
In times of stress adrenaline is released by the body.
One of the effects of this hormone is to raise the blood glucose concentration to allow more respiration to occur..

Question 7

summary of glucose concentration regulation

Answer 7

Question 8

Control of insulin secretion:

Answer 8

When blood glucose concentration rises above the set level, this is detected by the ß cells in the islets of Langerhans and insulin is released.
The mechanism by which this occurs is as follows:

Question 9

Control of insulin secretion mechanism p1

Answer 9

At normal blood glucose concentration levels, potassium channels in the plasma membrane of ß cells are open and potassium ions diffuse out of the cell.
The inside of the cell is at a potential of -70 mV with respect to the outside of the cell.

When blood glucose concentration rises, glucose enters the cell by a glucose transporter.

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

Question 10

Control of insulin secretion mechanism p2

Answer 10

The ATP binds to potassium channels and causes them to close.
They are known as ATP-sensitive potassium channels.

As potassium ions can no longer diffuse out of the cell, the potential difference reduces to around -30 mV and depolarisation occurs.

Depolarisation causes the voltage-gated calcium channels to open.

Calcium ions enter the cell and cause secretory vesicles to release the insulin they contain by exocytosis.

Question 11

Control of insulin secretion:
diagram

Answer 11

Question 12

Diabetes and its control

Answer 12

To keep blood glucose concentration constant the body relies on the interaction between glucagon and insulin.
However, for over 300 million people in the world this system of regulation does not work properly.
They suffer from the chronic disease, diabetes mellitus (usually referred to as diabetes).
This means they are unable to metabolise carbohydrates properly, in particular glucose.

Question 13

If you suffer from diabetes…

Answer 13

your pancreas either does not produce enough insulin, or your body cannot effectively respond to the insulin produced.
This means that blood glucose concentration remains high.
Hyperglycaemia, or raised blood sugar, is a common effect of uncontrolled diabetes.
Over time this can lead to serious damage of many body systems, especially the nerves and blood vessels.

Question 14

common symptoms of diabetes

Answer 14

Question 15

Type 1 diabetes p1

Answer 15

Patients with type 1 diabetes are unable to produce insulin.
The B cells in the islets of Langerhans do not produce insulin.
The cause of type I diabetes is not known and so, at the moment, the disease cannot be prevented or cured.
It is possible, however, to treat the symptoms.

Question 16

Type 1 diabetes p2

Answer 16

Evidence suggests that in many cases the condition arises as a result of an autoimmune response where the body’s own immune system attacks the ß cells.
This condition normally begins in childhood, and people develop symptoms of the disease quickly.

Question 17

Type 2 diabetes p1

Answer 17

Patients with type 2 diabetes cannot effectively use insulin and control their blood sugar levels.
This is either because the person’s B cells do not produce enough insulin or the person’s body cells do not respond properly to insulin.
This is often because the glycoprotein insulin receptor on the cell membrane does not work properly.
The cells lose their responsiveness to insulin, and therefore do not take up enough glucose, leaving it in the bloodstream.

Question 18

Type 2 diabetes p2

Answer 18

Globally, approximately 90% of people with diabetes have type 2 diabetes.
This is largely as a result of excess body weight, physical inactivity, and habitual, excessive overeating of (refined) carbohydrates.
Symptoms are similar to those of type 1 diabetes, but are often less severe and develop slowly.
As a result, the disease is often only diagnosed after complications have already arisen.
Risk of type 2 diabetes increases with age.
Until recently, this type of diabetes was seen only in adults (normally over the age of 40), but it is now also occurring in children.

Question 19

Type 2 diabetes in recent years:

Answer 19

There has been a significant increase in the number of cases of diabetes diagnosed in the UK, rising from 1.4 million in 1996 to around 3 million in 2014.
It is estimated that there may be as many as 5 million sufferers of diabetes by 2025, with around 85% having type 2 diabetes.
A clear causal link has been established between obesity and the onset of type 2 diabetes.
This information has been used to launch initiatives to promote healthy eating and exercise.
These include, for example, the Change 4 Life campaign.
This is an example of where scientific evidence has been used to inform decision-making at a national level.

Question 20

Diabetes treatment:

Answer 20

Diabetes is not a curable disease, but it can be controlled successfully, allowing sufferers to lead a normal life.
Treatment differs for both types of diabetes.

Question 21

treatment for Type 1 diabetes p1

Answer 21

Type 1 diabetes is controlled by regular injections of insulin and is therefore said to be insulin-dependent.
People with the condition have to regularly test their blood glucose concentration, normally by pricking their finger.
The drop of blood is then analysed by a machine, which tells the person their blood glucose concentration.
Based on this concentration, the person can work out the dose of insulin they need to inject.
The insulin administered increases the amount of glucose absorbed by cells and causes glycogenesis to occur; resulting in a reduction of blood glucose concentration.
If a person with diabetes injects himself or herself with too much insulin, they may experience hypoglycaemia (very low blood glucose concentrations) that can result in unconsciousness.

Question 22

treatment for Type 1 diabetes p2

Answer 22

However, too low an insulin dose results in hyperglycaemia, which can also result in unconsciousness and death if left untreated.
Careful monitoring and dose regulation is therefore required.
blood glucose concentration and insulin levels vary in a person with type 1 diabetes, and a person without diabetes.
If the person with diabetes injects himself or herself with insulin, there will be a surge of insulin in their blood which will cause their blood glucose level to drop quickly.

Question 23

comparison of diabetic with non diabetic

Answer 23

Question 24

treatment for Type 2 diabetes:

Answer 24

The first line of control in type 2 diabetes is to regulate the person’s carbohydrate intake through their diet and matching this to their exercise levels.
This often involves increasing exercise levels.
Overweight people are also encouraged to lose weight.
In some cases, diet and exercise are not enough to control blood glucose concentration so drugs also have to be used.
These can include drugs that stimulate insulin production, drugs that slow down the rate at which the body absorbs glucose from the intestine, and ultimately even insulin injections.

Question 25

Medically produced insulin:

Answer 25

Originally, insulin was obtained from the pancreas of cows and pigs which had been slaughtered for food.
This process was difficult and expensive.
The insulin extracted could also cause allergic reactions as it differed slightly from human insulin.
In 1955, the structure of human insulin was identified and it is now made by genetically modified bacteria. This has a number of advantages:

Question 26

genetically modified bacteria. This has a number of advantages

Answer 26

• Human insulin is produced in a pure form
  this means it is less likely to cause allergic reactions.
• Insulin can be produced in much higher quantities.
• Production costs are much cheaper.
• People’s concerns over using animal products in humans, which may be religious or ethical, are overcome.