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• A gland is a group of cells that produces and releases one or more substances (a process known as secretion)
• The endocrine system is made up of endocrine glands that release chemical substances, known as hormones, into the blood stream.
• Compared to the nervous system, the effects of hormones are slower but they act for longer, so the endocrine system is used to control functions that do not need instant responses.
• Structures that make up the endocrine system


  Important structures in the endocrine system are:

  • Pituitary gland: a ‘master gland’ that makes hormones such as FSH and LH
  • Thyroid: produces thyroxine, which controls metabolic rates and affects growth
  • Pancreas: produces insulin, which regulates blood glucose levels
  • Adrenal glands: produces adrenaline
  • Testes (males): produce testosterone
  • Ovaries (females): produce oestrogen

  
• Adrenaline is known as the 'fight or flight' hormone as it is produced in situations where the body may be in danger.
• Adrenaline causes a range of different things to happen in the body, all designed to prepare it for movement (i.e. fight or flight).
• An increase in heart rate and breathing rate occurs due to adrenaline, ensuring glucose and oxygen can be delivered to muscle cells at a faster rate.
• Diverting blood flow towards muscles and away from non-essential parts of the body such as the alimentary canal is a function of adrenaline, ensuring an increased supply of the reactants of respiration (glucose and oxygen).
• Dilation of the blood vessels inside muscles occurs due to adrenaline, ensuring more blood can circulate through them, supplying more glucose and oxygen.
• Breaking down of stored glycogen to glucose in the liver and muscle cells, with glucose released by the liver being transported to active muscle cells, is a function of adrenaline, ensuring a higher blood glucose concentration for increased respiration in muscle cells, providing greater energy for movement.