Hormones

• Light passes through


  Before reaching the retina
• Answers on page 102
• Hormones


  Chemical messengers, produced by glands, that travel in the blood to bring about a response in a target organ
• Main differences between hormones and nervous system


  • Method of communication: Nervous system - Electrical impulses along neurones, Hormones - Chemicals in blood
  • Speed of action: Nervous system - Fast-acting, Hormones - Usually slow-acting
• Hormones


  • Insulin
• Insulin and blood glucose


  Both responses are controlled by the brain
• Hormones


  • Controlling the concentration of glucose
  • Controlling the water content of the body known as osmoregulation
• Hormones usually act more slowly than the nervous system and over a large period of time
• Sex hormones (oestrogen and testosterone)


  Bring about changes in females and males during puberty which takes place over many years