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Homeostasis-packet 2

Homeostasis-packet 2 - BMED 3100 Systems Physiology I...

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BMED 3100: Systems Physiology 1 I. HOMEOSTASIS INTRO Homeostasis (Greek homoios -the same; stasis-standing): a dynamic steady state, representing the net effect of all turnover reactions. Homeostasis is the maintenance of relatively constant conditions within the body's internal environment. Many physiological parameters, such as blood glucose and body temperature, are precisely regulated by a homeostatic mechanism. Maintaining homeostasis is central to survival of individual cells and to the individual. Claude Bernard (mid-1800s): “la fixité du milieu intérieur..” “the constancy of the internal environment”. "The constancy (or: inflexibility) of the interior medium (or: environment) is the [basic] condition for independent and free life" Walter Cannon (1929): coined the word homeostasis . Cannon’s postulates : 1. Role of the autonomic nervous system: coordination of other systems 2. Tonic control of physiologic activity: ‘more’ or ‘less’, not ‘on’ or ‘off’ 3. Antagonistic control of physiologic activity: opposites control ‘up’ and ‘down’ 4. Chemicals signals can have different effects in different tissues Response Arc/Loop : 3 major components; begin with a stimulus and end with a response: 1) input signal 2) integration of the signal 3) output signal Broken down more: A. Stimulus Input to the system B. Receptors/sensors : Central (primary senses) Peripheral : a. Mechanoreceptor (e.g., baroreceptor, proprioceptor a. Nociceptors / Thermoreceptor b. Chemoreceptor (e.g., osmoreceptor) C. Afferent Pathway - Always carries information from receptor to integrating center a. Varies according to reflex type b. Endocrine reflex has no afferent pathway Receptor potential : change in membrane permeability Threshold : minimum stimulus necessary to initiate response; the greater above the threshold, the greater the action potential frequency Adaptation : e.g., pacinian corpuscle – pressure, viscoelastic structure Detect deviations from "set point";
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