5.4.4: Regulating blood glucose

Question 1

What is the normal blood concentration of blood glucose?

Answer 1

Between 4 and 6 mmol dm-3

Question 2

What happens If a person’s blood glucose concentration is allowed to drop below 4mmol dm-3 and remain too low for long periods?

Answer 2

The person is said to be hypoglycemic.

Question 3

What is the main problem caused by hypoglycemia?

Answer 3

There is an inadequate delivery of glucose to the body tissues and, in particular, to the brain.

Question 4

What can mild hypoglycemia cause?

Answer 4

tiredness and irritability.

Question 5

What happens in severe cases of hypoglycemia?

Answer 5

There may be impairment of brain function and confusion, which may lead on to seizures, unconsciousness and even death.

Question 6

What happens if blood glucose concentration is allowed to rise too high for long periods?

Answer 6

Hyperglycemia.

Question 7

What can permanently high blood glucose concentrations lead to?

Answer 7

Significant organ damage.

Question 8

What is a blood glucose concentration that is consistently higher than 7 mmol dm-3 used as the diagnosis for?

Answer 8

Diabetes mellitus

Question 9

Which cells constantly monitor the blood glucose concentrations?

Answer 9

The cells in the islets of Langerhans.

Question 10

What happens if blood glucose concentrations rise or fall away from the acceptable concentrations.

Answer 10

The alpha and beta cells in the islets of Langerhans detect the change and respond by releasing the relevant hormone.
Too high - insulin
Too low - glucagon

Question 11

What do the hormones released by the islets of Langerhans act on?

Answer 11

Cells in the liver (hepatocytes) which can store glucose in the form of glycogen.

Question 12

When there is excess glucose in the blood, what happens to it?

Answer 12

It is converted to glycogen.

Question 13

What happens if blood glucose concentration needs to be raised?

Answer 13

The glycogen is converted back into glucose.

Question 14

Which cells in the islets of Langerhans detect high blood glucose concentration?

Answer 14

The beta cells.

Question 15

How do the beta cells respond to high blood glucose concentrations?

Answer 15

-They excrete insulin into the blood.
-Insulin travels through the body in the circulatory system .
The target cells are the liver cells, muscle cells and some other body cells including the brain.

Question 16

Why is insulin unable to pass through the cell surface membrane?

Answer 16

Because it is a small protein of 51 amino acids.

Question 17

Describe the action of insulin on the liver cells.

Answer 17

• The target cell possesses the specific membrane bound receptors for insulin.
• When insulin binds to the insulin receptor, this activates the enzyme tyrosine kinase which is associated with the receptor on the inside of the membrane.
• Tyrosine kinase causes phosphorylation of inactive enzymes in the cell.
• This activates the enzymes leading to a cascade of enzyme-controlled reactions inside the cell.

Question 18

What effects does insulin have on the cell?

Answer 18

• More transporter proteins specific to glucose are placed into the cell surface membrane. This is achieved by causing vesicles containing these transporter proteins to fuse with the membrane.
• More glucose enters the cells.
• Glucose in the cell is converted to glycogen for storage (glycogenesis).
• More glucose is converted into fats.
• More glucose is used in respiration.

Question 19

Which cells in the islets of Langerhans detect low blood glucose concentration?

Answer 19

alpha cells

Question 20

How do the alpha cells respond to low blood glucose concentrations?

Answer 20

They secrete the hormone glucagon into the blood

Question 21

Why is glucagon unable to pass through the cell surface membrane?

Answer 21

Glucagon is a small protein containing 29 amino acids.

Question 22

What are the target cells of glucagon?

Answer 22

Hepatocytes which possess the specific receptor for glucagon.

Question 23

What is the effect of glucagon on a cell?

Answer 23

-Glycogen is converted into glucose (glycogenesis)

Question 24

What is the effect of glucagon on a cell?

Answer 24

• Glycogen is converted into glucose (glycogenolysis) by phosphorylase A, which is one of the enzymes activated in the cascade.
• More fatty acids used in respiration.
• Amino acids and fats converted into additional glucose, by gluconeogenesis.
• Overall=increase in blood glucose concentration

Question 25

The concentration of blood glucose is controlled by a negative feedback mechanism involving which hormones?
Describe how these hormones are antagonistic.

Answer 25

• Insulin and glucagon.
• They have opposite effects on blood glucose concentration.
• One of the effects is to inhibit the effects of the opposing hormone.