thermoregulation Flashcards
what is the process of thermoregulation?
- maintaining a constant core body temperature
what is the definition of heat?
- energy that is transferred from an object at a higher temperature to a lower temperature object
- dependent on volume/ mass
what is the definition of temperature?
- quantitive measure of how hot/ cold an object is, or the intensity of heat in an object
- independent of mass/ volume
what is the definition of specific heat capacity?
- amount of heat energy it takes to change the temperature of different substances by same amount
- specific heat of water greater than others so generate more heat before body temp rises by 1 degree
describe endotherms
- heat is generated during metabolism
- don’t rely on energy of sunlight
e.g. humans
what is the percentage of energy wasted in physical activity compared to the amount that yields external work ?
- 75 to 80% wasted as heat
- 20 to 25% yields external work
what are humans described as?
- homeotherms as they maintain body temperatures within very narrow limits
describe the difference between body core temperature and body surface temperature
- body core temperature maintained within narrow limits whereas body surface temperature can vary
- body core temp does fluctuate e.g. eating, exercise
can periphery of our bodies fluctuate?
- yes because they contain less vital organs so no adverse effects
why are variations in surface temperature important?
- bodies detect environmental changes early and signal appropriate response
what is the normal body core temp and how is it maintained?
- 37 degrees maintained by hypothalamus as thermosensors in hypothalamus and skin send signals to effectors which carry out responses
describe link of body temp regulation to circadian rhythm
- circadian fluctuation in body core temp of 1 degree
when is body temp lowest/ highest? what other factor may affect the temperature?
- lowest during night
- highest during day
- seasonal rhythms
how does gender affect body tempersture?
- in women body core temperature is higher during the second half of menstrual cycle due to progesterone
describe evaporation
- loss of heat via sweating
- only way we lose heat to environment when temp is higher than body
describe convection
- movement of layer surrounding the skin
- direct contact between a body and surrounding fluid
describe conduction
- body can gain/ lose heat depending on temp of the adjacent surface
- type of materials that bodies consist of affects rate at which heat is transferred
describe radiation
- emission of heat in form of EM waves
- body can either absorb or emit heat depending on ambient conditions
what is the thermoneutral zone ?
- when we can maintain our homeostatic body temp through changes in vasomotor tone (vasodilation/ vasoconstriction)
- without energy expenditure/ external influence
when is there a minimum metabolic rate?
- when core temperature is within neutral zone
how is body temp maintained?
- balancing of heat gain and heat loss
describe effect of temperature being too cooled vs too warm
- too cooled= enzymatic reactions in bodies slow down so less mobile and at risk of losing consciousness
-too warm = enzymes at risk of denaturing and losing function
describe mechanisms for heat loss
- blood reaching the skin
- sweating
describe physiological control of heat loss
thermosensors> central command > adrenal medulla> blood vessels dilate> sweat glands secrete fluid> heat loss to environment> body temp normal
when does vasodilation occur? what happens?
- thermoregulatory response to heat
- occurs in blood vessels in skin near extremities
- happens due to less sympathetic stimulation/ release of Ach
what does vasodilation support and what happens once at surface?
- supports skin metabolism
- once at surface, heat can be lost via radiation, conduction to environment
describe eccrine sweat glands involvement in heat loss
- deliver a hypotonic solution to skin’s surface; process of vaporisation removes heat from the body
describe role of thermoreceptors in heat loss
- sense changes in external temperature and signal this to hypothalamus which integrates info with other info e.g. blood temp> stimulates structures to initiate appropriate response
when does sweating occur? what innervates it?
- thermoregulatory response to heat
- sweat glands innervated by cholinergic nerve fibres via stimulation of muscarinic receptors
- catecholamines stimulate sweat production
what does swear production rate affect?
- composition of sweat with larger amounts of Na+ and Cl- being lost at high sweat rates
- rate of evaporation influenced by relative humidity
what are the two main sweat glands?
- eccrine = most common
- aporine = found in head follicle
what processes occur during heat production ?
- shivering thermogenesis
- voluntary muscular activity
- non- shivering thermogenesis
when does vasoconstriction occur? what happens?
- thermoregulatory response to cold
- blood vessels in skin innervated by sympathetic adrenergic fibres
- norephedrine acts on adrenergic fibres
- if blood flow is stopped for a while it can lead to frost bite
what is the hunting reaction?
- protective measure to stop frostbite (ischaemic injury)
- during long exposure to cold skin circulation shows intermittent periods of vasodilation
describe shivering thermogenesis
- thermoregulatory response to cold
- involuntary muscular contraction releases heat due to ATP breakdown
- all the energy contracted is converted to heat, no external work
what is shivering the result of?
- stimulation by somatic motor neurons
what is non- shivering thermogenesis?
- occurs from brown fat metabolism
- important for children
how is arrector pili muscle involved in heat conservation?
- contracts to produce goose bumps as it pulls on hair follicles to create a small depression on skin’s surface so surrounding areas protrudes
how do body hairs keep up warm?
- trap pockets of insulating air so heat less likely to be lost to environment
- piloerection occurs when sympathetic NS triggers body hair to stand erect
what is subcutaneous fat involvement in heat conservation ?
- good heat insulator so conducts heat poorly so when environment is cold it provides a layer of insulation to retain body heat
what is hypothermia?
- low body temperature
- functions impacted when core body temperature is under 35 degrees
what responses are insufficient in hypothermia?
- normal peripheral vasoconstriction and shivering responses
- so shivering becomes violent and muscle activity becomes slow
what are the symptoms of hypothermia? how is it treated?
- confusion, irritability, reduced respiratory rate
- treated via rewarming but not rapid as can lead lead to circulatory failure and shock
describe the body’s response at 36, 35, 33 and 29 degrees
- 36> shivering, less strength and power
- 35> max shivering+ decrease in performance
- 33> cardiac arrythmia
- 29> unconsciousness
what is hyperthermia?
- high body temperature; higher the body temperature means the more risk of damage to cells/ proteins
describe mild hyperthermia compared to severe hyperthermia
- mild= heat exhaustion
- severe= heat stroke (failure of thermoregulation with body temperature over 40.6)
what are the symptoms of hyperthermia?
- dizziness, disorientation, dry skin, high heart rate, collapse
how should hyperthermia be treated?
- vigorously using measures to cool the body
- rehydration
what happens during exercise to body temperature?
- body temp maintained higher> rest
- ^ heat production set point resetting has implications for muscle contractions
- activates heat loss mechanisms
what does thermoregulation decreases? what is its capacity and what is it limited by?
- decreases exercise capacity
- thermoregulation capacity is finite
- limited by homeostatic demands
what is the reduction in endurance performance during self paced time trials in heat?
- 2 to 25 percent
what work to elevate the set point?
- pyrogens are chemicals that induce fever as they are released into bloodstream by invading cells or own immune system
what do pyrogens work to do?
- elevate the hypothalamic set point to higher temperature
what does resetting of our thermostat cause us to do?
- rapidly generate heat in order to reach the new set point
- results in pyrexia (fever)
what happens in recovery of fever?
- set point returns to its normal value
- bodies engage in activities to lose excess heat
what happens when the hypothalamic set point is elevated?
- addition of layers, shivering, vasoconstriction, pale appearance
what happens when the hypothalamic set point returns to normal?
- removal of layers, sweating, vasodilation, flushed
why may fevers be beneficial?
- may assist the recovery process by enhancing activity of immune system
describe acclimatisation
- individual regulates body temperature efficiently
- occurs via repeated exposure to heat either in hot climate ( 2 weeks) or use of environmental chambers (5-10 days)
describe what acclimatised individuals will be able to do
- sweat more and sooner
- more diluted sweat (less electrolytes)
- more blood flow to skin
- increases blood volume/ stroke volume
- decreased body core temp, HR, glycogen use and fatigue
