Regulating temperature

External temperature change  Detected by heat and cool receptors on skin  External temperature may fluctuate without damage to humans

Internal temperature change  Detection by receptors within body  Receptors in hypothalamus of brain are most important  Some also near spinal column, around veins, in digestive system  All send messages to hypothalamus

Hypothalamus  Detects and receives messages about temperature change  Temperature control centre

Maintaining core temperature  Mammals = 37 degrees Celsius  At any time mammals both lose and produce heat Ways of gaining heatWays of losing heat Basic metabolic processesEvaporation of sweat ShiveringPanting Exercise/ vigorous activityConvection Radiation and conduction to body Radiation and conduction from body

Loss of heat Type of heat lossWhat is it?How much heat is lost? Radiation- Heat radiates from body in all directions. - Can also be absorbed by body from hotter objects ~60% of heat loss Conduction and convection -Transfer of heat from body to objects or substances that are touched. -Touched objects must be cooler than body temperature - If air surrounding body is moving (wind), convection currents take heat away from body -Convection occurs much faster in water than air ~ 15% of heat loss Evaporation-Occurs even when person is not “sweating” - Requires heat provided by body ~22% of heat loss

Temperature regulation by hypothalamus Normal temperature Check temperature Temperature normal Abnormal temperature Hypothalamus either increases heat production OR increases heat loss

Heat gain (or reduction of heat loss) ProcessDescription Heat production by shivering Hypothalamus sends message to muscles to involuntarily contract and relax rapidly. Cannot be sustained for too long due to energy requirements. Heat produced by metabolism Hypothalamus stimulates the pituatary gland, which then stimulates the thyroid, which increases its output of hormone thyroxine, which increases the metabolic rate in every cell in the body, releasing heat energy. Adrenaline can also be stimulated, which also increases metabolic rate Constriction of blood flow in skin When cold, blood vessels shrink, which decreases the surface area of the blood vessels, from which heat can escape. Blood vessels are also removed from the skin surface, keeping heat within the body Piloerection“Hair standing on end”. Not important for heat conservation in humans, but in other mammals, erect hairs trap air close to the body, which acts like a doona. It is caused by the contraction of muscles at the base of the hair.

Cooling down behaviour  Animals that don’t sweat will lick their paws  Seeking out a cool position to sleep (conserve energy and therefore heat)  Increase surface area, which increases the area by which heat can leave the body  Drinking water doesn’t cool us down, but reduces the danger of dehydration/ dessication

Size matters  A small animal will lose heat more quickly than a larger animal because of an increase in SA:V ratio  Therefore, the metabolism of an animal with a large surface area is much quicker, as it must produce more heat energy to maintain its temperature

Heat source Poikilothermic – Have a fluctuating (changing) body temperature Homeothermic – have a constant body temperature Endothermic – heat source is built into body CamelsHumans Ectothermic – temperature is reliant on external environment ReptilesNone – too fragile Ectotherms need significantly less food than endotherms. Why do you think this is?

Activities Glossary: ectothermic, endothermic, poikilothermic, homeothermic, hypothalamus, pituatary, adrenalin Quick Check questions pg 317

Land animals: adaptations to heat  Spinifex mouse Lives in well insulated burrow to keep temp. fairly constant Endothermic

Land animals: adaptations to heat  Snakes Bask in sun to heat up (ectothermic) Cold at night More active during day than night Cannot engage in prolonged strenuous activity, as lactic acid builds up in ectotherms’ muscles Some snakes may flatten themselves while basking (why?) Blood flow near skin is high while basking to heat blood as much as possible

Land animals: survival in cold  Ice can be deadly Enzymes do not function quickly Chemical reactions often happen in water. They cannot happen in ice. If a cell freezes, the ice crystals will expand and rupture the cell membrane.

How to prevent freezing  Increased dissolved salts in antifreeze substances that can be released into body fluids Glycerol, amino acids, sugars, salts Decreases freezing point of water (to about -18 degrees C) eg. Insects, fish, turtles, frogs

How to prevent freezing  Increased body fat (insulation)  Conversion of food to heat energy (eg. birds and mammals)  Lower surface area to reduce area of heat loss

Behavioural prevention of freezing  Burrowing underground (insulation)  Migration

A long sleep  Some animals hibernate or go into a torpor  Metabolism is drastically reduced (can be as low as 0.6% of normal rate) so animal only barely lives  Body temp drops to environmental temperature  Mountain Pygmy Possum lives in alpine areas of Victoria and NSW

Animals surviving in water  Aquatic environments have less temperature variation than terrestrial environments  Maintenance of body temperature may be by counter-current systems to warm the blood Outgoing artery paired with incoming vein. Therefore, blood cooled by being close to the skin is warmed by artery blood before reaching the inner core of the body Otherwise, aquatic mammals, like dolphins/whales/seals, have a thick layer of fat (blubber) to insulate against the cold water

Lack of oxygen in aquatic mammals  Aquatic mammals live largely under water but must breathe gaseous oxygen Higher oxygen carrying capabilities in blood Large lungs and other respiratory structures Storage of oxygen in other body tissues

Activities Glossary: counter-current, hibernation, torpor, antifreeze Quick Check questions pg 322