Homeostasis and Feedback

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

What needs to be regulated? Nutrients – oxygen, glucose, proteins etc. Electrolytes – salts (muscle contractions nerve transmission) Waste concentrations – CO 2, urea (nitrogen wastes), bile pH Temperature Pressure/volume – gases in blood, lungs

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

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

Thermostat Analogy Body Sensors = sensory nerves Controller = Hypothalamus in brain send signals to muscles via nerves Effector = muscles Long term: endocrine system increases thyroid activity to raise metabolic rate to increase heat production from cellular respiration

Body Temperature Effectors Muscles/circulatory constrict peripheral (arms and legs) blood flow, Muscles at follicles raise hairs, Skeletal muscles contract (shiver) generate heat Heart rate slows to keep blood concentrated in core body Skeletal muscle adjust body curls up

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

Clotting signals continue until clot is complete