Lecture 7

• Homeostasis


  The process of maintaining a constant internal environment despite changing conditions
• Homeostasis


  • Isn't equilibrium
  • Dynamic steady state
  • Oscillation around a setpoint

  
• Negative feedback


  Stabilizing mechanism for homeostasis

  
• Positive feedback


  Reinforcing mechanism, not for homeostasis
• Negative feedback for cortisol secretion

  Cortisol suppresses CRH and ACTH release
• Positive feedback for oxytocin and uterine contractions


  Reinforcing mechanism, not for homeostasis
• Cell-cell communication


  • Involves nervous system or endocrine system
  • Endocrine system communicates via hormones
• Hormones


  • Chemicals made by cells in specific endocrine glands or other tissues
  • Transported in blood to distant targets
  • Bind to specific receptors
  • May act on multiple tissues
  • Alter activity of target cells
  • Action must be terminated
  • Maintain homeostasis or precipitate change in many physiological processes
• Identifying hormones


  1. Remove gland & observe results

  2. Replace gland

  3. Replace extract from gland

  4. Give excess gland (or extract)

  5. Purify extract & test in biological assay
• Homeostasis is a core concept in physiology that requires cell-cell communication

  
• The endocrine system communicates via messengers known as hormones
• Hormones produced in endocrine glands have various effects on target cells