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Introduction Physiology: Study of the function and relationship of the various organ systems
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The body Made of 40% solid particles and 60% H2O The percentage of H2O varies with age, sex Babies: up to 80% H2O Older, slim person: 60%
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Figure 1.4
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Fluid compartments 2/3 cell fluid (intracellular fluid=ICF) 1/3 fluid outside the cell extracellular fluid (ECF) - 80% interstitial fluid (IF) - 20% circulating fluid – mostly plasma + CSF + eye and ear fluid
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Figure 1.5
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Homeostasis The process of maintaining a constant internal environment despite changing external environment Components: - Sensors - Integrating center - Effectors
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Regulatory mechanisms: Negative feedback: the most common Positive feedback: rare (ex:blood coagulation, parturition) Most parameters controlling body function (heart rate, breathing rate, blood pressure, blood glucose..) are maintained within a narrow range
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Negative feedback If a parameter value increases, body mechanisms works to bring the value down, within normal range The most common mechanism
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Positive feedback As a value increases, the body reacts to increase the value further Example: parturition (labor and delivery) and blood clotting
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Regulation of body temperature Body heat is a by-product of muscle contraction Heat losses or gains are due to: - convection: transfer of energy through moving gases or liquids - conduction: transfer of heat energy between objects in direct contact - radiation: transfer of energy through electromagnetic waves - evaporation: loss of heat when water is evaporating
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Body temperature regulation Normal body temperature = 37 o C = 98.6 o F If external temperature is high body reacts to cool down -skin: flush appearance due to blood vessel dilation, sweating -Heart rate increases -Respiratory rate increases If external temperature is low body reacts to warm up -skin: pale appearance due to blood vessel constriction, goose bumps -Heart rate decreases -Respiratory rate decreases -Muscle shivering
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Figure 1-4
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Mechanism of regulation Temperature receptors in the skin and deep within the body send temperature information to the temperature integrating center in the hypothalamus The integrating center makes a decision about the adjustments to be made Effectors in charge of adjusting the temperature are activated
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If body temperature is too cold:
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Body temperature regulation Normal body temperature = 37 o C = 98.6 o F If external temperature is high body reacts to cool down -skin: flush appearance due to blood vessel dilation, sweating -Heart rate increases -Respiratory rate increases
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Pathology of temperature regulation: heat exhaustion -A person is working in the sun, is hot, sweat and drinks large amount of water -The electrolytes (salts) lost through sweating are not replaced risk of seizures, loss of consciousness and death -Treatment: give fluids and electrolytes (ex: gatorade)
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Pathology of temperature regulation: heat stroke A person is working in the sun, is hot. The sun increases body and especially brain temperature -If the brain temperature reaches too high level, the brain becomes unable to react sweating stops -Body temperature reach very high levels the person dies
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So what is fever? Body temperature can be as high as 35-36 o C (105-106 o F), despite external temperatures being much cooler. Pathogens invade the body macrophages fight against the infection and in the process secrete a special compound, a pyrogen. A pyrogen has the ability to reset the body’s internal temperature to a higher level When it does, the body reacts to increase its temperature shivering, … fever When the body has won its battle against the pathogen, the macrophages no longer secrete pyrogen. However, the body temperature is high the temperature center in the hypothalamus direct the body to cool down sweating ….
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Readings Chp. 1: p2-20. Book pages corresponding to notes. Clinical connections: p 10
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