Endocrine System

• Hormones


  Only act on target cells
• Target cells


  Only respond to their hormone (like jigsaw pieces)
• Hormones are secreted in very small quantities and are broken down when they pass through the liver and are excreted in urine
• Hormone acting on Target cells

  Stile link here
• Nerves


  • Fast acting and have short term effects
• Hormones


  • Respond slower but have longer lasting effects. This reduces the amount of the hormones that need to be produced
• Fight or flight response


  1. Adrenalin (released by the adrenal glands) causes:

  2. Pupils to dilate

  3. Hair to stand on end

  4. An increase in heart rate and breathing rate

  5. Increase in blood to the muscles

  6. Brain to be alert
• Glands and their hormones


  • Ovary / Oestrogen & Progesterone - Controls menstrual cycle/stimulates ovaries to release eggs/controls pregnancy
  • Adrenal / adrenaline - Prepares body for fight or flight, increases heart rate, dilates pupils, makes hairs stand up
  • Pancreas / Insulin & glucagon - Stimulates liver to store glucose if levels are high or stimulates liver to release glucose if levels are too low
  • Thyroid / Thyroxin - Controls the rate of chemical reactions in cells. Regulates metabolism
  • Testes (male only) / Testosterone - Controls reproductive system. Stimulates hair growth
  • Pituitary - Thyroid stimulating hormone plus others - Master gland, controls many other glands by releasing hormones
• The pituitary gland receives messages from the hypothalamus in the brain. It is a link between the nervous and endocrine systems
• Pituitary gland


  Releases hormones that act directly on cells and instruct other glands to release hormones
• Homeostasis


  The maintenance of a constant internal environment despite changes in surroundings
• To allow cells to work efficiently, temperature, glucose levels and water must be kept within strict limits
• Controlling Blood Glucose - High

  1. Pancreas detects this (receptor)

  2. Pancreas releases insulin

  3. Insulin signals liver and body cells to store glucose

  4. Glucose level returns to normal
• Controlling Blood Glucose - Low

  1. Pancreas detects this (receptor)

  2. Pancreas releases glucagon

  3. Glucagon signals liver and body cells to release glucose

  4. Glucose level returns to normal
• Homeostasis is maintained through negative feedback systems that stabilise the internal environment by reversing changes within it