A Quick Review Modified from J.Pheifer Auburn High School

 The body’s ability to adjust to a fluctuating internal and external environment.  In homeostasis the body maintains balance, or steady state, despite environmental fluctuations.  Dynamic Equilibrium – the body is always in active balance.

….systems that receive information, react and respond to maintain homeostasis

 Mechanism that make adjustment to bring the body back to an acceptable range (homeostasis)  Coordinating centre  Monitor  Regulator The thermostat as an example of homeostasis

 Primary feedback system in the body:  Negative Feedback Resists change  Homeostasis occurs with the help of: Coordinating Center Monitors Regulators

 Special receptors found throughout the body.  Receptors are specialized – unique jobs  specific receptors that sense blood sugar levels; specific receptors that sense body temperature; and much more!!!  Receptors sense when limits are not at the normal limit/range.  Send message to coordinating center to alert of the imbalance.

 The Brain  Where the normal limits are set.  Receives messages from monitors.  Relays messages to the appropriate regulator.

 Organ(s) of the body that respond to the brain’s message to bring body back into balance (homeostasis)  Examples:  The liver releases glucose to restore blood sugar levels.  Blood vessels constrict near skin to keep heat in the body, when internal temperature drops.  Skin emits sweat when hot, to reduce internal temperature.

Maintaining Homeostasis Negative Feedback System examples

 Moves the controlled variable even further away from a steady state (homeostasis)  Less common in the body.  Reinforces the change  A good example is the birth process:  Decrease in progesterone – initiate small contraction in the uterus  Contractions cause release of the hormone oxytocin. Oxytocin causes stronger contractions.  Baby moves towards cervix causing even more oxytocin to be released – continues until baby is expelled  Once expelled – uterine contractions stop – causing oxytocin to stop.

 Homeostasis refers to the body’s attempt to adjust to a fluctuating external environment.  All homeostatic control systems have three functional components: a monitor, a coordinating centre, and a regulator.  Negative feedback mechanisms trigger a response that reverses the changed condition.  Positive feedback systems move the controlled variable even further away from a steady state.