Blood glucose concentration Flashcards
Glycogenesis
The synthesis of glycogen from glucose
Glycogenolysis
The breakdown of glycogen into glucose
Gluconeogenesis
The synthesis of glucose from non-carbohydrates e,g glycerol and amino acids
What happens if blood glucose concentration is too high?
Lowers the water potential of the blood so water moves out of the cells and into the blood - can cause cells to shrivel up and die.
What happens if blood glucose concentration is too low?
Cells cannot carry out normal functions as there isn’t enough glucose for respiration to provide energy
When is insulin secreted?
When the blood glucose concentration is too high!!
When is glucagon secreted?
When the blood glucose concentration is too low!!
What are the 3 roles of insulin?
attaching to specific receptors on surfaces of target cells
controlling the uptake of glucose by regulating the inclusion of channel proteins in the surface membranes of target cells
Activating enzymes in the conversion of glucose to glycogen (glycogenesis)
What is the overall role of insulin?
To lower the blood glucose concentration
What are the 3 roles of glucagon?
attaching to receptors on the surface of target cells
activating enzymes involved in the conversion of glycogen to glucose (glycogenolysis)
activating enzymes involved in the conversion of glycerol and amino acids to glycogen (gluconeogenesis)
What is the overall role of glucagon?
To raise the blood glucose concentration
Describe how insulin lowers the blood glucose concentration?
Binds to specific receptors on the surfaces of muscle and liver cells (hepatocytes)
Increases the permeability to glucose of muscle cell membranes so cells take up more glucose
It increases permeability by increasing the number of channel proteins in cell membranes
Activates enzymes in muscle and liver cells that convert glucose –> glycogen (stored in cells cytoplasm as energy source)
Increases the rate if respiration of glucose, especially in muscle cells.
Describe how glucagon rasies the blood glucose concentration?
Binds to specific receptors on cell membranes of liver cells
Activates enzymes that break down glycogen into glucose (glycogenolysis)
Activates enzymes involved in the formation of glucose from amino acids and glycerol (non-carbs) - gluconeogenesis
Lowers the rate of respiration of glucose in cells
What detects low and high blood glucose concentration?
The pancreas
Where are the alpha and beta cells found in the pancreas?
Islets of Langerhans
Which cell secretes insulin?
Beta cells
Which cell secretes glucagon?
Alpha cells
What are glucose transporters?
They are channel proteins which allow glucose to be transported across a cell membrane.
Which glucose transporter do skeletal and cardiac muscle cells contain?
GLUT4
What is the state of GLUT4 when insulin levels are low?
Stored in vesicles in the cell cytoplasm
What happens to GLUT4 when insulin binds to the specific receptors found on the cell membranes of target cells? e.g. liver or muscle cells
Triggers the movement of GLUT4 towards the membrane. Glucose can then be transported into the cell through the GLUT4 channel protein BY FACILITATED DIFFUSION
Where is adrenaline secreted from?
The adrenal glands
Why is adrenaline secreted?
When there is a low concentration of glucose in the blood (e.g. stressed/exercising)
How does adrenaline increase blood glucose concentration?
Activates glycogenelysis
Inhibits glycogenesis
Activates glucagon secretion
Inhibits insulin secretion
which both = increase in blood glucose concentration
Where does adrenaline bind?
To the receptors in the cell membrane of liver cells
How does adrenaline get the body ready for ‘action’?
makes more glucose available for muscles to respire
What does the second messenger model allow glucagon and adrenaline to do?
When they bind to the specific receptors on the outside of the cell - it allows them to activate glycogenolysis inside the cell.
How does the second messenger model work?
The binding of the hormone to the receptors on the outside of the cell activates an enzyme on the inside of the cell membrane which produces a chemical known as a second messenger.
The second messenger activates other enzymes which bring about a response.
In order to activate glycogenolysis which enzymes do glucagon and adrenaline activate when they bind to their receptors?
Adenylate cyclase (aka adenylyl cyclase)
What does activated adenylate cyclase do?
It converts ATP into a chemical called cAMP (cyclic AMP)
What is cAMP?
Cyclic AMP - which is a second messenger
What enzymes does cAMP activate?
Protein kinase A
What does protein kinase A activate?
A series of chain reactions (a cascade) which causes the breakdown of glycogen into glucose
