homeostasis

• Homeostasis - the monitoring and response to any deviation from the bodies steady state
• Adjacent cells communicate using chemicals that move by diffusion and bond to receptors e.g. in the immune system

  Cells communicate over long distances using hormones that travel in the blood or neurones

  
• Receptor cells detect internal and external stimuli
• Feedback systems are used to correct levels when they are two low or to high. These can be hormonal, nerve impulses or both.

  
• Glucose control

  • Glucose level increases
  • Receptors in pancreas cause insulin to be released
  • Insulin targets liver and other cells to increase uptake of glucose and store it as glycogen
  • Blood glucose levels decrease to normal
  • Glucose levels decrease
  • Receptors in pancreas cause glucagon to be released
  • Glucagon targets liver causing the break down of glycogen and the release of glucose into the blood
  • Glucose levels increase
• Negative feedback is where a change is levels is detected and returned to normal

  
• Temperature control

  • Temperature increases
  • Decreases in temperature causes the hypothalamus to send a signal to the skin and skeletal muscles.
  • Skin blood vessels dilate and sweat gland to activate
  • Increase in temperature causes the hypothalamus to send a signal to the skin and sweat glands.
  • Body temperature decreases to normal levels
  • Body temperature increased back to normal levels 
  • Body temperature decreases
• Positive feedback is where a change is detected and increased for example blood clot formation, urination, lactation and labour 

  
• Labour

  • Baby pushes on the cervix causing it to stretch.
  • Oxytocin caused the uterus to contract
  • Nerve impulse is sent to the brain.
  • The brain stimulates the pituitary to release oxytocin.
  • This causes the baby to push on the cervix, causing it to stretch.