Blood Glucose Concentration

Biology: Cambridge International A Level, topic 14.4.1

Maintaining Blood Glucose Concentration

Blood glucose concentration is controlled by homeostasis. The normal concentration is 90 mg 100 cm⁻³. It is important to maintain a stable blood glucose concentration for two reasons:

Meeting respiratory demands

Glucose is a respiratory substrate.
There must be enough glucose in the blood to meet the demands of respiring cells.
If glucose levels are too low, respiration rate will slow.

Maintaining water potential

Glucose can affect the water potential of the blood.
An increase in blood glucose concentration will decrease the water potential of the blood.
Water will move out of tissues into the blood by osmosis. This causes dehydration of the cells and the cells will die.
Blood pressure also increases.

Factors Affecting Blood Glucose Levels

Blood glucose concentration must be monitored carefully to make sure there is a constant supply of glucose for respiration. Blood glucose levels can be influenced by:

Eating

Eating carbohydrates causes an increase in blood glucose concentration.
Increases in blood glucose levels are monitored by the pancreas.

Exercise

Exercising causes a decrease in blood glucose concentration because glucose is being used in respiration to power muscle contraction.
Decreases in blood glucose levels are also monitored by the pancreas.

Measuring glucose

Glucose concentration can be measured in the blood or urine.
Urine dipstick tests contain glucose oxidase and peroxidase enzymes.
A dipstick is placed in the urine of an individual. If glucose is present, these enzymes convert glucose into a coloured product visible on the dipstick.
Glucose in urine can be suggestive of diabetes.

The Liver

The liver is an organ that plays an important role in controlling blood glucose concentration. The processes that take place in the liver are:

Glycogenesis

When blood glucose concentration is too high, the liver cells produce enzymes that convert glucose into glycogen. This glycogen is then stored in the liver cells.
This process is called glycogenesis.

Glycogenolysis

When blood glucose concentration is too low, the liver cells produce enzymes that break down the glycogen stored in the cells to glucose.
This process is called glycogenolysis.

Gluconeogenesis

When blood glucose concentration is too low, liver cells also form glucose from glycerol and amino acids.
This process is called gluconeogenesis.

Test yourself on Blood Glucose Concentration

What are the two reasons for maintining blood glucose concentration?
Which of the following statements about blood glucose concentration are true?
What is the effect of an increase in blood glucose concentration on the cells in the body?
Where are changes (increase/decrease) in blood glucose levels detected?
Why is more glucose used during exercise than at rest?

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