Homeostasis and Feedback

1. Homeostasis and Feedback

2. Homeo = Similar Stasis = State • Maintaining a stable internal environment within a narrow range • Necessary for proper function of enzymes that carry out all metabolic processes • Involves all organ systems

3. What needs to be regulated? • Nutrients – oxygen, glucose, proteins etc. • Electrolytes – salts (muscle contractions nerve transmission) • Waste concentrations – CO2, urea (nitrogen wastes), bile • pH • Temperature • Pressure/volume – gases in blood, lungs

4. How to regulate • Set point – what is the desired range? • Sensors – structures including receptors on target cells that will monitor levels relative to set point • Controller – determine if levels are within set point range and what response is necessary to return to range • Effector – parts of body that physically make the change to return to set point range

6. Negative Feedback • Any change from the normal range is opposed (thus negative) • This brings it back within optimal range and decreases the chaos in the body • Most systems in body are negative feedback as they maintain the balance • Examples – body temperature, blood sugar

7. Thermostat Analogy Body Sensors = sensory nerves Controller = Hypothalamus in brain Send signals via nerves Effectors = muscles/circulatory constrict peripheral blood flow, Muscles at follicles raise hairs, Skeletal muscles contract (shiver) generate heat, Heart rate slows blood concentrated in core, Skeletal muscle adjust body posture closes Long term: endocrine system increases thyroid activity to raise metabolic rate and increase heat production from cellular respiration

9. Positive feedback • Reinforces the original stimulus – pushing conditions further from the normal • Less common as it can get out of control and will not stop until stimulus is removed • Increases chaos in body systems • Examples – blood clotting and child birth