The regulation of blood glucose concentration

Question 1

What is the pancreas

Answer 1

• The pancreas is a large, pale-coloured gland that is situated in the upper abdomen, behind the stomach.
• It produces enzymes for digestion (protease,amylase,lipase).
• It produces hormones for regulating blood glucose concentration (insulin, glucagon).

Question 2

What are the hormone-producing cells scattered throughout the cells that produce digestive enzymes in the pancreas called

Answer 2

Islets of Langerhans

Question 3

What type of cell is the pancreas mostly made up of when examined under a microscope

Answer 3

Cells that produce digestive enzymes

Question 4

What do the cells of the islets of Lanherhans include

Answer 4

• a-cells which are larger and produce the hormone glucagon.
• b-cells, which are smaller and produce the hormone insulin.

Question 5

What are the cells that the liver is made up of called

Answer 5

Hepatocytes

Question 6

List the three important processes associated with regulating blood sugar which take place in the liver

Answer 6

1) Glycogenesis
2) Glycogenolysis
3) Gluconeogenesis

Question 7

Explain what glycogenesis is

Answer 7

• Glycogenesis is the conversion of glucose into glycogen.
• When blood glucose concentration is higher than normal the liver removes glucose from the blood and converts it to glycogen.
• It can store 75-100g of glycogen, which is sufficient to maintain a humans blood glucose concentration for about 12 hours when at rest, in the absence of other sources.

Question 8

Explain what glycogenolysis is

Answer 8

• Glycogenolysis is the breakdown of glycogen to glucose.
• When blood glucose concentration is lower than normal, the liver can convert stored glycogen back into glucose which diffuses into the blood to restore the normal blood glucose concentration.

Question 9

Explain what gluconeogenesis is

Answer 9

• Gluconeogenesis is the production of glucose from sources other than carbohydrate.
• When its supply of glycogen is exhausted, the liver can produce glucose from non-carbohydrate sources such as glycerol and amino acids.

Question 10

Why is it important that blood glucose concentration doesn’t falls too low

Answer 10

• If the concentration falls to low, cells will be deprived of energy and die as glucose is needed for respiration.
• brain cells are especially sensitive in this respect because they can only respire glucose.

Question 11

Why is it important that blood glucose concentration doesn’t rise to high

Answer 11

• If the concentration rises to high, it lowers the water potential of the blood.
• This creates osmotic problems that can cause dehydration and be incredibly dangerous.

Question 12

What are the three sources of blood glucose

Answer 12

1) Directly from the diet: glucose absorbed following hydrolysis of other carbohydrates such as starch, maltose, lactose and sucrose.
2) Glycogenolysis: from the hydrolysis in the small intestine of glycogen stored in the liver and muscle cells.
3) Gluconeogenesis: the production of glucose from sources other than carbohydrate.

Question 13

What are the three main hormones involved in the regulation of blood glucose concentration

Answer 13

Insulin, glucagon and adrenaline

Question 14

What type of protein is insulin and how many amino acids is it made up of

Answer 14

Insulin is a globular protein made up of 51 amino acids.

Question 15

Describe the first stage in how insulin lowers blood glucose concentration

Answer 15

• The B-cells of the islets of Langerhans in the pancreas have receptors that detect the stimulus of a rise in blood glucose concentration.
• They respond by secreting the hormone insulin directly into the blood plasma.
• Almost all body cells (red blood cells being an exception) have glycoprotein receptors on their cell-surface membranes that bind specifically with insulin molecules.
• When it combines with the receptors insulin brings about changes that help to lower blood glucose concentration.

Question 16

Describe the second stage in how insulin lowers blood glucose concentrations (what is causes once it binds to receptors on cells)

Answer 16

• When it binds to receptors insulin brings about:
• A change in the tertiary structure of the glucose transport carrier proteins, causing them to change shape and open, allowing more glucose into the cells by facilitated diffusion.
• An increase in the number of carrier proteins responsible for glucose transport in the cell surface membrane.
• At low insulin concentrations, the protein form which these channels are made is part of the membrane of vesicles.
• A rise in insulin concentration results in these vesicles fusing with the cell-surface membrane so increasing the number of glucose transport channels.
• Activation of the enzymes that convert glucose to glycogen and fat.

Question 17

Describe the third stage in the lowering of blood glucose concentration by insulin- how the changes insulin initiates when it binds to receptors result in the lowering of blood glucose

Answer 17

• The blood glucose is lowered by insulin in the following ways:
• By increasing the rate of absorption of glucose into the cells, especially the muscle cells.
• By increasing the respiratory rate of the cells, which therefore use up more glucose, thus increasing their uptake of glucose from the blood.
• By increasing the rate of conversion of glucose into glycogen (glycogenesis) in the cells of the liver and muscles.
• By increasing the rate of conversion of glucose to fat.

Question 18

Describe how the a-cells of the islets of Langerhans help to control blood glucose concentration

Answer 18

• The a-cells in the islets of Langerhans detect a fall in blood glucose concentration and respond by secreting the hormone glucagon directly into the blood plasma.
• Glucagons actions include:
• attaching to specific protein receptors on the cell-surface membrane of liver cells.
• Activating enzymes that convert glycogen to glucose.
• activating enzymes involved in the conversion of amino acids and glycerol into glucose (gluconeogenesis).
• The overall effect is therefore to increase the concentration of glucose in the blood and return it to its optimum.

Question 19

Where and when is adrenaline produced

Answer 19

At time of excitement or stress, adrenaline is produced by the adrenal glands that lie above the kidneys.

Question 20

How does adrenaline raise blood glucose concentration

Answer 20

• By attaching to protein receptors on the cell-surface membrane of target cells.
• By activating enzymes that causes the breakdown of glycogen to glucose in the liver.

Question 21

How do insulin and glucagon act in reference to each other

Answer 21

• Antagonistically.
• Glucagon increases blood glucose concentration whereas insulin decreases blood glucose concentration.

Question 22

What is type I (insulin dependant) diabetes

Answer 22

• Type I diabetes is due to the body being unable to produce insulin.
• It normally begins in childhood.
• It may be the result of an autoimmune response whereby the bodies immune system attacks its own cells, in this cause the B-cells in the islets of Langerhans.
• Type I diabetes develops quickly, usually over a few weeks.

Question 23

What is type II (insulin independent) diabetes

Answer 23

• Type II diabetes is normally due to the glycoprotein receptors on body cells being lost or losing their responsiveness to insulin.
• However, it may also be due to an inadequate supply of insulin from the pancreas.
• Type II diabetes usually develops in people over the age of 40 years.
• There is an increasing number of cases of obesity and poor diet leading to type II diabetes in adolescents.
• It develops slowly, and the symptoms are normally less severe and may go unnoticed.
• People who are overweight are particularly likely to develop type II diabetes.

Question 24

Describe how type I diabetes is treated

Answer 24

• Type I diabetes is controlled by injections of insulin.
• This cannot be taken by mouth because, being a protein, it would be digested in the alimentary canal.
• It is therefore injected, typically either two or four times a day.
• The dose of insulin must be matched exactly to the glucose intake.
  -If a person with diabetes takes too much insulin they will experience a low blood glucose concentration that can result in unconsciousness.
• To ensure the correct dose, blood glucose concentration is monitored using biosensors.
• By injecting insulin and managing their carbohydrate intake and exercise carefully, people with diabetes can lead normal lives.

Question 25

Describe how type II diabetes is treated

Answer 25

• Type II diabetes is usually controlled by regulating the intake of carbohydrate in the diet and matching this to the amount of exercise taken.
• In some cases, this may be supplemented by injections of insulin or by the use of drugs that stimulate insulin production.
• Other drugs can slow down the rate at which the body absorbs glucose from the intestine.