Control of Blood Glucose Concentration
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Why does blood glucose concentration vary?
It depends on food intake and energy requirements
What is the normal range of blood glucose concentration?
About 70–99 mg/dl
Why must blood glucose be kept within a narrow range?
To ensure essential processes such as brain cell respiration continue
What happens if blood glucose concentration is too high?
Glucose is excreted in urine and cannot be stored
Why is excreted glucose useless to the body?
It cannot be stored as glycogen or fat
What organ regulates blood glucose levels?
The liver
What is glycogenesis?
The conversion of glucose into glycogen
What is glycogenolysis?
The breakdown of glycogen into glucose
What is gluconeogenesis?
The synthesis of glucose from non-carbohydrate molecules such as amino acids
When does glycogenesis occur?
When blood glucose concentration is high
Which cells detect a rise in blood glucose?
Beta cells
Where are beta cells located?
In the islets of Langerhans in the pancreas
What hormone do beta cells secrete?
Insulin
What effect does insulin have on alpha cells?
It inhibits them
What cells does insulin target?
Hepatocytes, muscle cells and fat cells
How does insulin travel to its target cells?
Through the blood
What happens when insulin binds to receptors on target cells?
Glucose transport protein vesicles fuse with the membrane
What is the effect of more glucose transport proteins?
Increased permeability to glucose
What happens to glucose once inside the cell?
It is converted to glycogen or fat or used in respiration
When does blood glucose concentration fall?
Between meals or during exercise
Which cells detect a fall in blood glucose?
Alpha cells
What hormone do alpha cells secrete?
Glucagon
What effect does glucagon have on beta cells?
It inhibits them
What effect does glucagon have on hepatocytes?
It stimulates glycogenolysis
What happens to glucose after glycogen is broken down?
It diffuses into the blood
What fuels do cells use when glucose is low?
Fatty acids and amino acids
What is adrenaline?
A hormone that acts as a secondary messenger system
What is the first step of adrenaline action?
Adrenaline binds to a receptor on the liver cell membrane
What happens to the receptor when adrenaline binds?
It changes shape inside the membrane
What enzyme is activated by the receptor shape change?
Adenyl cyclase
What does adenyl cyclase do?
Converts ATP into cyclic AMP (cAMP)
What is cAMP?
A second messenger
What does cAMP activate?
Protein kinase
What is the effect of protein kinase?
It catalyses the breakdown of glycogen into glucose
What is diabetes?
A condition where blood glucose regulation is impaired
What are the two types of diabetes?
Type 1 and Type 2
What is Type 1 diabetes?
Insulin-dependent diabetes
When does Type 1 diabetes usually develop?
Early in life
What causes Type 1 diabetes?
Loss of insulin production due to destruction of beta cells
How is Type 1 diabetes managed?
Insulin injections matched to diet and exercise
What is Type 2 diabetes?
Non-insulin-dependent diabetes
When does Type 2 diabetes usually develop?
Later in life
What causes Type 2 diabetes?
Reduced insulin production or unresponsive insulin receptors
What lifestyle factors contribute to Type 2 diabetes?
Obesity and poor diet
How can Type 2 diabetes be controlled?
Diet management and exercise
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