Warming and cooling

responses to high temperature

vasodilation, pilorelaxation, sweating, gular fluttering, panting, behavioural changes

responses to low temperatures

vasoconstriction, piloerection, moulting, shivering, brown adipose tissue (BAT), behavioural changes

vasodilation

arterioles dilate, which allows more blood to enter the capillaries in the skin

vasoconstriction

arterioles constrict, so less blood enters the capillaries to flow through the skin

pilorelaxation

pilli erector muscles relax which lowers the hairs/feathers on the skin so that air can circulate - allows for convection and evaporation

piloerection

pilli erector muscles contract causing hairs or feathers on the skin to be raised. This traps a layer of insulating air, reducing heat transfer from the skin

sweating

glands secrete sweat onto the skin, where it evaporates and takes heat from the body

adrenal and thyroid glands secrete adrenaline and thyroxine which reduces metabolic rate and therefore heat generation

an evaporative cooling mechanism

gular fluttering

increases heat loss through the mouth

occurs in bird, where they rapidly flap membranes in the throat to increase evaporation

an evaporative cooling mechanism

panting

evaporation of water from within the nasal passages, mouth, lungs, and (in birds) air sacs. Used by many mammals, reptiles and birds

an evaporative cooling mechanism

behavioural changes in response to high temperature

stretching out the body - gives larger surface area for heat loss

animals may seek shade and move less

behavioural changes in response to low temperature

curling up - smaller surface area for heat to escape

move to warmer areas

show increased movement

shivering

muscles contract and relax rapidly and cause heat to be produced by friction and respiration

brown adipose tissue (BAT)

cells take lipids and run them through the mitochondria to generate heat

present in almost all mammals

found in greater quantities in neonates and hibernating animals

how can endotherms regulate internal body temperature?

by adjusting their metabolic rate

because metabolic reactions give off heat

counter current mechanism for heat regulation

heat is exchanged between two sources flowing in opposite directions

in heat regulation, these sources are the bloodstream

when body temp drops, arteries carry warm oxygenated blood away from the heart while veins carry old deoxygenated blood towards the heart. As they both pass, the warm arterial blood transfers most of its heat to the cool venous blood and body temperature is balanced

hypothermia

body cannot maintain normal temperature

3 phases: mild symptoms - weakness, shivering, lack of alertness

moderate symptoms - muscle stiffness, low blood pressure, slow breathing

severe symptoms - fixed/dilated pupils, inaudible heartbeat, difficulty breathing, coma

can result in death

hyperthermia

elevation of body temperature above the normal

fever hyperthermia - results from inflammation within the body e.g. due to infection

non-fever - results from all other causes of increased body temperature e.g. excessive exercise, excessive levels of thyroid hormones

symptoms: panting, dehydration, reddening of gums, decease of urination, uncoordinated movements and unconsciousness

can lead to multiple organ dysfunction and death