The Endocrine System

• The other way to send information around the body (apart from along nerves) is by using hormones
• Hormones are chemical messengers sent in the blood
• Hormones are chemical molecules released directly into the blood. They're carried in the blood to other parts of the body, but only affect particular cells in particular organs (called target organs)
• Hormones control things in organs and cells that need constant adjustment
• Hormones are produced in (and secreted by) various glands, called endocrine glands. These glands made up the endocrine system
• Hormones tend to have relatively long-lasting effects
• The pituitary gland:

  • The pituitary gland produces many hormones that regulate body conditions
  • It's sometimes called the 'master gland' because these hormones act on other glands, directing them to release hormones that bring about change

  
• Ovaries - females only

  • Produce oestrogen, which is involved in the menstural cycle

  
• Testes - males only

  • Produce testosterone, which controls puberty and sperm production in males

  
• Thyroid:

  • This produces thyroxine, which is involved in regulating things like the rate of metabolism, heart rate and temperature

  
• Adrenal gland:

  • This produces adrenaline, which is used to prepare the body for a 'fight or flight' response

  
• The pancreas:

  • This produces insulin, which is used to regulate the blood glucose level

  
• Hormones and nerves have differences
• Nerves:

  • Very fast action
  • Act for a very short time
  • Act on a very precise area
• Hormones:

  • Slower action
  • Act for a long time
  • Act in a more general way
• If the response is really quick, it's probably nervous. Some information needs to be passed to effectors really quickly (e.g. pain signals, or information from your eyes), so it's no good using hormones to carry the message - they're too slow
• If a response lasts for a long time, it's probably hormonal. E.g. when you get a shock, a hormone called adrenaline is released into your body (causing the fight or flight response, where your body is hyped up ready for action). You can tell it's a hormonal response (even though it kicks in quickly) because you feel a bit wobbly for a while afterwards