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POSITIVE AND NEGATIVE FEEDBACK, MARIN, REFERENCES: PubMed: effects of…
POSITIVE AND NEGATIVE FEEDBACK
POSITIVE
Positive feedback is when the body amplifies a stimulus, moving the values of a system away from its set point that is required for homeostasis until an external signal or event stops the cycle
Ex: Hypothermia causing delirium, which makes people remove their clothes and get colder, leave safety and shelter, and have visual or auditory hallucinations
Ex: Hormone levels changing after the birth of a baby to make the mother accept the infant
NEGATIVE
Keeps values close to a set point
Thermoregulation by sweating to cool/restore set point, vasoconstriction and shivering to heat back up
Majority of homeostasis processes are negative feedback loops (positive feedback is often in extreme dangerous conditions or physiological malfunction, like in the case of hypothermia)
RECEPTORS: receive information that something in the environment is changing
Chemoreceptor
Located on tongue, nose, in blood and tissue
Taste/gustatory receptors (detect dissolved chemicals in food-- flavors), carotid bodies (peripheral receptors at the base of arteries, detect dissolved gases and hypoxia/hypercapnia)
Respond to chemicals, solute concentrations (osmoreceptors), blood pH, CO2 levels, prostaglandins
Thermoreceptor
Respond to heat, cold, and certain food chemicals (e.g. capsaicin)
Located on skin and hypothalamus (peripheral/external and central/internal)
TRP (transient receptor potential), protein in neurons that detects temperature change, Kraus end bulbs in dermis that detect cold, and Ruffini endings (dendritic, detect warmth)
Mechanoreceptor
Responds to mechanical stress, pressure, sound waves, gravity
Pacinian corpuscles (respond to vibration and pressure), Ruffini ending (provide information about skin stretch, helping grip)
Located on skin, in blood vessels, in ears
Photoreceptor
Respond to visible light
Located in eye (rod and cone cells)
Rod cells responsible for vision in low light, cone cells less sensitive but enable color vision and detail perception in bright light (scotopic vs photopic)
THERMOREGULATION & EXERCISE
Exercising increases core temperature due to muscle contraction, which is detected by central thermoreceptors
In cold environments, hypothalamus detects temperature through thermoreceptors (peripheral, central)
Heat conserving/generating responds like vasoconstriction to reduce heat loss to environment, shivering by muscle contraction
Hypothalamus activates cooling -- vasodilation to release heat, perspiration for evaporative cooling
When combined, opposing responses from two different negative feedback loops combine -- e.g. at the start, heat conservation is prioritized until the individual generates enough heat through exercise for excess heat to be available to be lost
Core temp can be high while skin temp is low because of conditions (evaporative/conductive cooling from wind/rain)
Higher risk of hypothermia or sever stress (can induce dangerous positive feedback) because if a person suddenly rests, drop in metabolic rate/exercise can plunge core temp
Energy expenditure is much higher in cold, wet conditions than moderate/dry ones, exhaustion occurs faster and can be more dangerous if not regulated
MARIN
REFERENCES:
PubMed: effects of environment on temperature
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Rain and metabolic strain
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Sage Journals
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NIH Thermoregulation
, Biozone , class slides