5.5.11 Coordination of Responses

Question 1

What is the mechanism of the ‘fight or flight’ response

Answer 1

• Sensory neurones detect environmental stimuli associated with danger
• Impulses sent to brain
• Amygdala (region of brain) sends impulses to hypothalamus
• Hypothalamus sends impulses to adrenal glands via sympathetic nerves
• Adrenal medulla secretes adrenaline
• Adrenaline stimulates target organs to increase in sensory awareness, thus more alert
• Hypothalamus also releases hormones stimulating pituitary gland
• Pituitary gland secretes ACTH
• Transported to adrenal glands
• Causes adrenal cortex to release cortisol
• Stimulates target organs and tissue to increase blood pressure and blood glucose
• Ensures enough energy is required for muscles to carry out a response, eg run.
• Cortisol also suppresses immune system

Question 2

Examples of effects of adrenaline

Answer 2

• Decreases blood flow to gut
• Increases blood flow to brain and muscles (vasodilation)
• Heartrate and stroke volume increase
• Stimulates breakdown of glycogen into glucose
• Increases diameter of bronchioles

Question 3

What is the secondary messenger model regarding glycogen?

Answer 3

• Adrenaline binds to receptors on surface of liver cells
• Adenylyl cyclase becomes activated
• Catalyses conversion of ATP to second messenger cyclic AMP
• Cyclic AMP binds to protein kinase A enzymes activating them
• Phosphate groups added to Kinase A enzyme activates phosphorylase kinase enzyme
• Active phosphorylase kinase enzyme activates glycogen phosphorylase enzyme
• Active glycogen phosphorylase catalyses breakdown of glycogen to glucose
• Glycogenolysis
• Increases blood glucose levels, increases respiration