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What are the 2 main ways systemic temperature is controlled?
- Heat production
- Heat dissipation
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What structure coordinates the body's response to change in core temperature?
Hypothalamus
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What are some ways that the body produces heat?
- Basal rate of ellular metabolism
- Metabolism due to muscle acitivity
- Increased metabolism due to thyroxine (thyroid hormone)
- Norepi, epi, and sympathetic stimulation of cells
- Increased cell metabolism with temperature increases
- Cellular metabolism for digestion, absorption, and storage of food
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Most body heat is produced in what deep organs?
Liver, brain, heart, skeletal muscles
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What does the body have as insulators?
- Skin
- Subcutaneous tissue
- Subcutaneous fat
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What is a part of hte heat radiator system?
Skin blood flow
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Degree of vasoconstriction of the skin vasculature determines what?
Heat conduction by the skin
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Sympathetic system acts in response to:
- Body core temperature
- Changes in environmental temperature
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What is radiation?
Transfer of heat in the form of infrared rays
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Radiation accounts for how much heat loss from the body?
60%
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What is conduction?
Kinetic energy of molecular motion is transferred (as heat) from the skin to the environment
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When does conduction NOT occur?
What are and skin temperature are the same
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What is convection?
Heat loss from the body due to air currents
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What two heat loss systems are increased when submerged in water?
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Sweating is controlled by what?
ANS (sympathetic) in response to body temperature
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What is responsible for signaling the sympathetics to increase sweating?
Anterior hypothalamus
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Sympathetic system innervation to sweat glands utilizes what neurotransmitter?
Acteylcholine
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What stimulates glandular cell secretion?
Cholinergic fibers
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Composition of initial sweat is similar to what?
Plasma
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Where are some temperature receptors?
- Receptors in skin to monitor surface temperature
- Deep body temp receptors (spinal coard, abdominal viscera, great veins)
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Deep receptors send their information where?
Posterior hypothalamus
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Increased body temp stimulates:
- Vasodilation of skin vessels (inhibit sympathetics)
- Increased sweating (stimulate sympathetics)
- Inhibition of excess heat production (chemical thermogenesis)
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Decreased body temp stimulates:
- Vasoconstriction of cutaneous vessels
- Piloeretion
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What are some ways we can increase thermogenesis?
- Shivering
- Sympathetic stimulation of chemical thermogenesis
- Thyroxine secretion
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What is shivering?
Increase in muscle tone beyond normal threshold stimulates shivering
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How much can shivering increase body heat production?
4-5X
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What neurotransmitters are capable of "uncoupling" oxidative phosphorylation?
Norepi and epi
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What is the cascade for creating tyroxine?
Hypothalamus-> TRH -> TSH -> T4 (thyroxine)
- TRH - thyrotropin releasing hormone
- TSH - thyroid stimulating hormone
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What is the "set point"?
98.6 degrees F
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What is fever?
Body temperature above normal range
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What stimulates the hypothalamus to increase core body temperature?
Prostaglandins
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What OTC medicines do we use to inhibit prostaglandin formation?
Aspirin & Tylenol
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What are the 3 phases of fever?
- Phase 1 - increase in core temperature
- Phase 2 - Maintenance of increased temperature
- Phase 3 - Resolution of fever; Return to normal core temperature; Crisis/Flush
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During phase 1 in fever, why do we feel chills?
The hypothalamus has increased the set point and the actually body temp is below it, so shivering increases the body temp to reach the new higher set point.
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In phase 3, why do we sweat?
When the fever breaks, the hypothalamus lowers the set point. At that point the body temp is still high from the fever, so we sweat to derease to try and reduce the temperature to return to the now-set-to-normal set point
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What causes spasms in muscles?
- Fluid level and electrolyte imbalance
- NaCl lost via sweat
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What are some symptoms of heat exhaustion?
Weak, rapid pulse, low BP, headache, dizziness, general weakness
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What causes heat exhaustion?
Excessive sweating causes ineffective circulatory adjustments (reduced perfusion to body)
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At what temperature is it considered heat stroke?
104 degrees F
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What are the symptoms of heat stroke?
Dry, hot skin, headache, fatigue, confusion, vomiting, unconsciousness
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