Control of blood glucose concentration Flashcards
What is the normal concentration of blood glucose?
90mg per 100cm3
What monitors the concentration of blood glucose?
Cells in the pancreas
When does blood glucose rise?
After eating food containing carbohydrate
When does blood glucose fall?
After exercise as more glucose is used in respiration to release energy, when you’re stressed
What two hormones are used to control the concentration of blood glucose?
Insulin
Glucagon
What is a hormone?
A chemical messenger which travels in blood to their target cells
Where is insulin and glucagon secreted from?
Clusters of cells called islets of Langerhans
What cells do the Islets of Langerhans contain?
Alpha cells
Beta cells
Delta cells
What do beta cells secrete?
Insulin into the blood
What do alpha cells secrete?
Glucagon into the blood
What are insulin and glucagon examples of?
Effectors
What role does insulin play in controlling blood glucose concentrations?
Lowers blood glucose concentration when its too high
How does insulin affect cell membranes?
It binds to specific receptors on the cell membranes of muscle and liver cells, increasing the permeability to glucose so more is taken up. Done by increasing the number of channel proteins
What enzymes does insulin activate?
Muscle and liver cells that convert glucose into glycogen
What is glycogenesis?
The formation of glycogen from glucose
What does insulin increase the rate of?
Rate of respiration of glucose
What role does glucagon play in controlling blood glucose concentrations?
Raises blood glucose concentration when its too low
How does glucagon work?
It binds to specific receptors on the cell membranes of liver cells and activates enzymes that break down glycogen into glucose
What process does glucagon activate?
Glycogenolysis
What is glycogenolysis?
The formation of glucose from glycogen
What is gluconeogenesis?
The formation of glucose from non-carbohydrates such as amino acids and glycerol
What is a weakness of a hormonal response to control blood glucose?
It is slower than a nerve impulse response
What is a strength of a hormonal response to control blood glucose?
They are not broken down as quickly as neurotransmitters so effects last longer
Explain how negative feedback mechanisms respond to a rise in blood glucose concentration?
- When it is detected by the pancreas, the β cells secrete insulin and the α cells stop secreting glucagon
- Insulin binds to receptors on liver and muscle cells
- The liver and muscle cells respond to decrease the blood glucose concentration
- Glycogenesis is activated
- Blood glucose concentration returns to normal
Explain how negative feedback mechanisms respond to a fall in blood glucose concentration?
- When it is detected by the pancreas, the α cells secrete glucagon and the β cells stop secreting insulin
- Glucagon binds to receptors on liver cells
- Liver cells respond to increase the blood glucose concentration
- Glycogenolysis is activated
- Blood glucose concentration returns to normal
What are glucose transporters?
Channel proteins which allow glucose to be transported across a cell membrane
What type of glucose transporter is in skeletal and cardiac muscle cells?
GLUT4
What happens to glucose transporters when insulin levels are low?
GLUT4 is stored in vesicles in the cytoplasm but when insulin binds it triggers the movement of GLUT4 to the membrane. Glucose can then be transported into the cell by the protein by facilitated diffusion
What is adrenaline?
A hormone secreted from adrenal glands
When is adrenaline secreted?
When there’s a low concentration of glucose in your blood
What two things does adrenaline do?
Binds to receptors in the cell membranes of liver cells and;
- Activates glycogenolysis (breakdown of glycogen to glucose)
- Inhibits glycogenesis ( the synthesis of glycogen from glucose
What does adrenaline get the body ready for?
Making more glucose available for muscles to respire
What is the secondary messenger model?
The binding of the hormone to cell receptors activates an enzyme on the inside of the cell membrane, which they produces a chemical known as a second messenger
What does a secondary messenger do?
Activates other enzymes in the cell to bring about a response
How does adrenaline and glucagon act in terms of the secondary messenger model and activating glycogenolysis? (step by step)
- To activate glycogenolysis, adrenaline and glucagon bind to their receptors and activate an enzyme called adenylate cyclase.
- Activated adenylate cyclase converts ATP into a chemical called cyclic AMP (cAMP) which is a secondary messenger
- cAMP activates an enzyme called protein kinase A
- Protein kinase A activates a chain of reactions which breaks down glycogen into glucose
Why are glucagon and adrenaline receptors complimentary in shape to their respective hormones?
They have a specific tertiary structure
