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5/11/2017 Homeostasis “The human body is not a thing or substance, given, but a continuous creation. The human body is an energy system which is never a complete structure; never static; is in perpetual inner selfconstruction and selfdestruction; we destroy in order to make it new.” HOMEOSTASIS • The bodies ultimate goal is to maintain a stable internal environment. • “The human body is a machine which winds its own springs.” ~Julien Offroy de la Mettrie, L'Homme Machine ~Norman O. Brown Homeostasis Homeostatic Imbalance • Dynamic Equilibrium • Not a “steady state”, as there is constant monitoring & adjusting Disease DEATH Disease Normal Range Disease Disease DEATH Feedback Mechanisms • Helps to keep the body within a livable range • Body tries to keep as close to a set point as possible • The LAST step in a series of events controls the FIRST • Disease = disturbance of homeostasis 3. INPUT Information sent along afferent pathway to control center 4. OUTPUT Information sent along efferent pathway to effector CONTROL CENTER Afferent Pathway RECEPTOR 1.STIMULUS Produces change in variable Control systems get less effective Internal environment less stable Increased risk of illness Changes in body that we associate with aging Negative Feedback Efferent pathway EFFECTOR 2. RECEPTORS Detect change – Can be negative or positive • WITH AGE: BALANCE 5. RESPONSE Effector reacts to information • Can be negative or positive feedback • CHANGE in one direction causes body to return conditions to “normal” • The final step INHIBITS the initial signal in the series 1 5/11/2017 EXAMPLE of Negative Feedback: Body Temperature Regulation Stimulus Stimulus TOO HOT Thermorecptors TOO COLD Sensory Neurons (Afferent) Control Center (in Brain) Motor Neurons (Efferent) SWEAT Skeletal Muscle Activates Glands Activate SHIVER Response Examples Positive Feedback = • CHANGE in one direction; enhances & accelerates original stimulus in a CASCADE effect • The final step STIMULATES the release of more initial signals EXAMPLE of Positive Feedback: Blood Clotting 2. Platelets stick to site 3. Released chemicals 4. Feedback Cycle 1. Break in blood attract more platelets Ends When: & release chemicals vessel wall Platelet plug is fully formed Homeostasis Examples Homeostasis Examples A sick child begins to sweat. A butcher slices his finger Regulation = body Temp. Feedback = negative Regulation = wound healing Feedback = positive Homeostasis Examples Homeostasis Examples Homeostasis Examples A man faints in the L&D room Snowy hunters shiver & huddle Frightened teens heart beats harder than normal Regulation = blood pressure Feedback = negative Regulation = body temp. Feedback = negative Regulation = blood pressure Feedback = negative 2 5/11/2017 Homeostasis Examples Homeostasis Examples Homeostasis Examples Uterine stretching and fetal head on cervix triggers labor Toddler eats too much candy Seamstress sews through her finger Regulation = labor & delivery Feedback = positive Regulation = blood glucose Feedback = negative Homeostasis Examples Homeostasis Examples Nursing mother’s milk supply changes with baby’s need Thirsty jogger drinks water Regulation = nursing Feedback = positive Regulation = wound healing Feedback = positive Questions? Comments? Regulation = hydration Feedback = negative 3