Adrenaline and the 'fight or flight' response

• The response of animals to stress is termed the ‘fight or flight’ response
• Has evolved as a protective mechanism enabling organisms to react quickly and be able to respond to life threatening situations
• This allows organisms to be prepared to 

  • Fight for survival 
  • Take flight (or quickly move away) from the danger
• The response usually begins when the sensory receptors transmit information to the hypothalamus 
• It is the hypothalamus, communicating via the nervous system, that sets up the ‘fight or flight’ response 
• Hypothalamus initiates is actions via the autonomic nervous system; a system linked to the control of breathing, blood pressure, heart rate and other involuntary actions
• It is the sympathetic component which is activated and prepares the body to respond to danger 
• Hormones are generally slow acting; however, adrenaline is a notable exception
• Adrenaline is involved in the ‘fight or flight response and is fast acting
• Adrenaline can be released into the bloodstream due to a variety of reasons such as danger, stress, shock and excitement
• These emotions cause the hypothalamus to activate nervous pathways (sympathetic nervous system), which in turn causes the release of adrenaline from the adrenal medulla (on top of the kidneys) into the bloodstream
• Adrenaline overrides the normal homeostatic control
• It inhibits the secretion of insulin and binds to specific protein receptors on the surface of the liver cells 
• This activates a series of steps that ultimately converts glycogen to glucose, increasing blood sugar levels
• This glucose can then be transported to cells to be used as energy for the ‘fight or flight response
• Adrenaline increases our alertness and prepares us to ‘fight’ or ‘run’ away from danger to increase our chance of survival 
• Physiological changes that adrenaline contributes to are 

  • Increase in heart rate 
  • Increase in blood pressure 
  • Dilation of bronchial tubes in lungs 
  • Dilation of pupils 
  • Increased blood flow to muscles 
  • Increased metabolic rate