thermoregulation Flashcards
Thermogenic mechanisms that increase ATP utilization
Increased Na/K ATPase activity Increased SERCA activity
Thermogenic mechanisms that reduce the efficiency of mitochondrial ATP synthesis
uncoupling of respiration from ATP synthesis by uncoupling protein (UCP) in brown adipose tissue Hormonal control
what are some factors that increase basal metabolic rate
thyroid hormone fever male sex hormone growth hormone
what are some factors that decrease basal metabolic rate
sleep malnutrition age (elderly feverish is lower BL)
what are some factors that impact heat production
Hormonal Skeletal muscle Liver metabolism Food Elevated body temperature
what is the equation and the definition of being thermally balanced
Heat storage =metabolism - work - evaporation ± radiation ± conduction ± convection Heat storage = 0 at core temperature When the heat storage is zero, the body is thermally balanced
what are TRP channels
transient receptor potential (TRP) channels -cation channels -implicated as cold and warm-sensing proteins
compare and contrast central versus peripheral thermosensors
Central thermosensors measure core temperature and trigger autonomic thermoregulatory responses peripheral thermosensors are more important for behavioral changes to assist the body in thermoregulation
compare and contrast cold and warm sensing
- Warm-sensing central thermoreceptors, located in the hypothalamus, spinal cord, viscera, and great veins, are more numerous than centrally located cold thermoreceptors. - can inhibit cold receptors - Cold sensing thermoreceptors are central- sensing thermoreceptors - most significant in terms of core temperature - more numerous in skin
identify 4 whole-body mechanisms of heat generation
Nonshivering thermogenesis
- not muscle activity
- brown fat tissue where oxidative phosphorylation is uncoupled from ATP production to produce heat instead
- Children, adults during as adaptation to cold, or hypersympathetic conditions such as adrenal medullary tumors.
Voluntary muscle activity
- Hypothalmus to the cortex
- passive (starting fire, active (running), eating
Involuntary muscle activity (shivering)
-activation of posterior hypothalamic neurons that are normally inhibited in normothermia a
Dietary thermogenesis
-describes the thermogenic effect of food, or more specifically, heat produced through metabolizing it.
how does the sympathetic system act to conserve or porduce heat
Sympathetic nervous system to conserve heat
- Piloerection
- vasoconstriction to conserve heat
Sympathetic nervous system to produce heat
Epi release creating non-shivering thermogenesis and hormone activation (THE MOST EFFECTIVE)
what occurs when the body drops below 77 F
heart fibrillation occurs when core temperature drops to around 77ºF
hypothalamic regulation is impaired when core temperatures drop only a few degrees below normal
As temperatures drop, sleepiness develops and coma follows due to central nervous system depression
Shivering will also cease due to this depression of the central nervous system
what are ways which we loose heat
Radiation causes heat loss in the form of infrared rays. This heat loss only occurs when the body surface is warmer than ambient temperature.
Conductive heat loss occurs by direct contact with an object. Not significant normally in terms of objects, but conductive loss to surrounding air is significant.
Convective heat loss results from air movement. Air currents moving across the surface of skin facilitates removal of heat that was first conducted to the air from the skin surface.
Conduction and convection of heat from a person suspended in water occurs much faster than in air due to the much higher specific heat of water and its much higher heat conductivity.
Evaporation includes sensible and insensible water loss. Sensible water loss includes sweating and can be regulated, whereas insensible loss describes water that passively diffuses through skin and respiratory surfaces and is lost to evaporation. Evaporation is the only means of losing heat from the skin surface when ambient temperatures are greater than body temperature. Children, due to their greater surface-to-mass ratio, rely more on the dry conduction of heat to air.
what controls heat conduction
Control of heat conduction to the skin is controlled almost completely by vasoconstriction initiated by the sympathetic nervous system
what is the most important mechanism of heat loss and how does it change with acclimation
Evaporation (sensible) aka sweating
sweat is normally hypotonic at low flow (Na+, Cl-reabsorbed) but becomes isotonic at high rates (more Na+, Cl-lost). As acclimation improves the function is improved and the sweat remains hypotonic at higher flow (aldosterone influenced)
there are also more sweat glands but the threshold for sweating decreases
summarize temperature regulation
