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Ventilation
- Exchange of air between the atmosphere and the alveoli
- Actual movement of respiratory gases at the terminal branches occurs due to diffusion
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Homeothermic
- Maintaining body temperatures within very narrow limits despite wide fluctuations in ambient temperature
- Allows chemical rxn in the body to take place regularly instead of fluctuating with a changing of internal temperature
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Shell body temperatures
- Heat loss surface-- skin
- Varies considerably
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Rectal temperature
- Usually 0.7 degrees higher than oral
- Core
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Axillary temperature
98.6 degrees but does not fluctuate with food, fluid intake
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Otic (ear) temperature resting
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Body temperature
- Usually maintained between 96 degrees and 100 degrees despite changes in external air
- Fluctuates about 1-1.8 degrees F in 24 hours (low in morning, high in late afternoon or evening)
- Reflects the balance between heat production and heat loss and heat retention
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Why do women have higher temperatures during the second half of the menstrual cycle?
- Effects of progesterone
- Spike on day 14, which is the basis of ovulation predictor kits
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What happens at 106 degrees F? 110?
- 106: convulsions; protein denaturation
- 110: absolute limits for life
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Skeletal muscle heat production during exercise
30-40 times that of the rest of the body
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Radiation
- Loss of heat in the form of electromagnetic or infrared waves (thermal energy)
- Any dense object that is warmer than the objects in its environment will transfer heat to those objects
- 60% of heat is lost through radiation
- Also gain heat by absorbing electromagnetic waves from the sun
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Conduction
- Transfer of heat between objects that are ihn direct contact with each other including the air or water
- Water is a better conductor of heat so more heat is lost to water than to air
- 15% of heat loss
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Convection
- Body shell transfers heat to surrounding air
- Process whereby conductive heat loss or gain is aided by movement of the air or water next to the body
- Warm air expands and rises while cool air falls
- Wind/fan is forced convection
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Evaporation
- Water evaporates bc its molecules absorb heat from the environment and becomes energetic enough, vibrate fast enough, to escape as gas (vapor)
- Removes large amounts of heat from the body surface
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Insensible perspiration
- Evaporation through the lungs, mucosa of the mouth, and through skin
- You can't feel it but you are sweating heat all the time
- 25% of heat loss
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Sensible perspiration
- Increase temperature, exercise/stress
- Sweat you can feel
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Why do people suffer heat exhaustion more frequently in humidity
- When it is wet outside, then you loose less of your own hot, wet water
- Dry heat allows you to sweat and you can be cooler
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Homeostasis of temperature
- 37 degrees C or 98.6 degrees F
- If heat producing mechanisms generate more heat than is lost, body temp rises
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Fever
- Too high body temp destroys proteins
- Controlled hyperthermia
- Results from infection somewhere in the body
- WBC release pyrogens which act directly on hypothalamus to reset thermostat to higher temperature
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Hypothermia
Too low body temp causes cardiac arrhythmias
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Hypothalamus
- The body's thermostat
- Controls heat production, heat loss and heat retention
- Receives input from peripheral thermoreceptors located in shell and central thermoreceptors
- Fever
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Two types of thermoreceptors
- Peripheral thermoreceptors (skin)
- Central thermoreceptors (deep body structures including the abdominal organs and hypothalamic neurons)-- Much more essential as core temperature must be kept constant
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Mechanisms of heat production
- Increase of metabolic rate (NE)
- Shivering (muscle contraction)
- Enhanced thyroxine release
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Increased metabolic rate for heat
- Norepinephrine release is stimulated by sympathetic fibers
- Increases metabolic rate which enhances heat production
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Shivering in heat production
Stretch receptors in antagonistic muscles are stimulated causing involuntary shuddering of skeletal muscles and therefore increase temperature
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Enhanced thyroxine release
- When environmental temperature decreases gradually (summer to winter), the hypothalamus releases thyrotropin releasing hormone, TRH
- Activates TSH and then more thyroxine which increases metabolic rate and increase body heat
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Vasodilation
- Heat loss mechanism
- This of cutaneous blood vessels by inhibition of sympathetic fibers causing vessels serving the skin to dilate
- Skin swells with warm blood
- You turn red
- Heat is lost by radiation, conduction and convection
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Sweating
- Sweat glands strongly activated by sympathetic fibers
- Heat is lost by evaporation
- Less so in humid air
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Decrease in insulation
Burning of fat stores causes a decrease in insulating subcutaneous layer, therefore heat loss increases
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Vasoconstriction of cutaneous blood vessels
- Blood vessels to the skin constrict keeping the blood closer to the core (heat stays in)
- Prolonged constriction leads to tissue damage (frostbite)
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Raynaud's syndrome
- Issue with blood vessels
- Prone to migraines
- No blood flow to fingers but there's flow to hands
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Other factors for heat retention
- Decrease sweat production
- Increased insulation (build fat)
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Piloerrection
- Arrector pili muscle contraction forces hair to stand straight up while dimpling skin
- Insulator mechanism for animals bc traps warm air in the layer of hair
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Mechanism of fever
- Phagocytes enter, they secrete chemical pyrogens that circulate to the hypothalamus which releases prostaglandins
- This increases the hypothalamic thermostat
Aspirin, ibuprofen, Tylenol all inhibit prostaglandins so reduce fever
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Chill stage of fever
- Increased pyrogens in blood raises the thermostat setting
- Causes the hypothalamus to respond to too low of body temp by stimulating heat production
- Even though body core's temp is rising, the skin remains cold and shivering occurs
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Fever breaks
- Decreased pyrogens in blood lowers the thermostat setting back to normal
- Causes hypothalamus to respond to too high of body temp
- Skin becomes warm and person sweats
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Crisis stage of fever
- Danger of fever that is if the thermostat is set too high
- Proteins may denature and permanent brain damage may occur
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Danger ranges body temp
Above 110 and below 75
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Hypothermia
- Decrease in body temp, reduces metabolic rate, can be deliberate (surgery) or accidental
- Subdivided into 4 different degrees: mild
- (90–95 °F); moderate, (82–90 °F); severe, (68–82 °F) and
- profound (at less than 68 °F)
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Difference between mild/moderate and severe/profound hypothermia
- Mild/Moderate Hypothermia: discomfort, shivering, apathy
- Severe/Profound Hypothermia: depressed body temp, absence of shivering, unconsciousness
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Heat exhaustion
- Body is trying to cool you
- Sweating, heat loss mechanisms caused by dehydration
- Temp may be elevated but not above 104
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Two types of heat exhaustion
- Water depletion: signs include excessive thirst, weakness, headache, and loss of consciousness
- Salt depletion: signs include nausea, vomiting, muscle cramps and dizziness
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Heat stroke
- Homeostasis fails, the body cannot control heat/temp anymore, rapid rise in temperature, rises to the point at which brain damage or damage to other internal organs may result Temperature may reach 105oF or greater
- Red, hot, dry skin
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Biggest differences between heat stroke and exhaustion
- Exhaustion: sweaty skin
- Massage cramping muscles
- Spray cool water
- Take cool shower
- Remove clothing
- Stroke: red, hot, dry
- Elevate pts feet higher than their head to reduce shock
- Remove clothing and cool with water
- Use ice packs and cool drinks
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