Thermoregulation 15.2+3 Flashcards
What is thermoregulation?
It is the maintenance of a constant core body temperature in order for enzymes to work at their optimum rates of activity
What can cause organisms to heat up?
- Exothermic chemical reactions e.g. waste heat from respiration
- Conduction from surroundings where the collision of molecules cause heat
- Convection from surroundings where warm air and water rises and sets up warm currents around the organism
`- Radiation from surroundings which are the transmission of electromagnetic waves from the surroundings.
What can cause organisms to cool down?
- Latent heat of vapourisation cools objects down when water evaporates from a surface
- Conduction to surroundings, transferring heat to molecules in surroundings by collision
- Convection to surroundings where cold air or water sinks and sets up cool currents around the person
- Radiation to surroundings
How is core temperature maintained?
By balancing the heating and cooling factors
What are ectotherms?
These are most animals that regulate their body temperature using their surroundings and their core body temperature depends on the environment.
Give examples of ectotherms
- Invertebrates
- Fish
- Reptiles
- Amphibians
Why do ectotherms living in water not have to thermoregulate but those on land do?
Water has a high specific heat capacity which means the temperature doesn’t change that much. On land, the temperature can really vary between seasons so they need to find ways to regulate their temperature
Ectotherms behavioural responses to warm up
- They need to warm up to increase metabolic reactions which keep them active
- Lizards bask in the sun to increase the radiation they absorb, so they orient their bodies or extend their body to maximise the surface area so more can be exposed to the sun
- Pressing their body to the warm ground for conduction
- Also vibrating by contracting their muscles for exothermic reactions to occur
Ectotherms behavioural responses to cool down
- They sometimes need to cool down to stop their enzymes from denaturing
- They take cover from the sun and move into shady areas, like cracks in rocks or burrows
- They press their body to cool rocks or water
- They limit activity and movement
Ectotherms physiological responses to warming
- Darker colours absorb more radiation than light colours so lizards in hotter places are lighter and lizards in colder places are darker
- They can also alter their heart rate to increase or decrease their metabolic rate
What are the advantages of ectotherms?
They need less food to survive as they don’t need energy to regulate their temperature and so they can survive in more difficult habitats
What are endotherms?
Endotherms are organisms that regulate their body temperature using metabolic processes so therefore they require a lot more energy than ectotherms
Give examples of endotherms?
Humans, other mammals and birds
Which receptors detect surface temperature in humans?
The peripheral temperature receptors
Which receptors detect blood temperature?
Temperature receptors in the hypothalamus which maintain the core temperatures by triggering a response
How do endotherms keep warm and cool down?
They use their internal exothermic metabolic activities to keep warm and their energy requiring reactions to cool down.
What behaviours do endotherms take part in to keep warm or cool down?
They also bask in the sun, press against hot or cold surfaces and do many behaviours that ectotherms do. They can also go into hibernation to avoid cold stress
What is the name for hibernation from hot weather?
This is called aestivation and is to avoid heat stress
What are the 3 physiological responses to cool down endotherms?
- Vasodilation
- Increased sweating
- Reducing insulation
Vasodilation
The arterioles near the surface of the skin dilate when the temperature rises and the arteriovenous shunt vessels ( the direct connection between arterioles and venules) will constrict which forces blood through the capillary networks close to the skin. The blood then cools down because of the increased radiation and the skin flushes. If the skin is pressed on a cold surface then the blood cools down by conduction
Increased sweating
As the core temperature increases, sweating increases and the sweat will spread out across the skin which then evaporate from the surface which cools the blood underneath. Cats lick themselves to keep cool for the same principle
Reducing insulating layers
When the body temperature increases, the pili muscles of the skin relax which means the hairs lay flat to avoid trapping insulating layers of air.
What adaptations do endotherms have in hot climates?
They also have their hair lie flat, they have light coloured fur or feathers to reflect radiation, they also have a large surface area to volume ratio to maximise heat loss.
Name 3 physiological responses that warm up endotherms?
- Vasoconstriction
- Decrease sweating
- Increase insulation
- Shivering
Vasoconstriction
This is where the arterioles near the surface of the skin contract and the arteriovenous shunt vessels dilate. The skin looks pale as not a lot of blood flows through there, and most of the blood is kept well below the surface. Not a lot of heat is radiated
Decreased sweating
When the core temperature drops, sweating will decrease and production will stop entirely to minimise the evaporation of it from the skin’s surface so more heat can be conserved
Increased insulation
When the body temperature falls, the erector pili muscles in the skin contract and pull the hairs up wards which traps an insulating layer of air around the skin to try and conserve heat.
Shivering
When the body temperature falls, shivering occurs. This is the involuntary contracting and relaxing of the large voluntary muscles which causes exothermic reactions to occur which release metabolic heat and warm the body up instead of it moving
What adaptations do endotherms have to cold climate?
- Reduced SA:V ratio to reduce cooling
- Long fur
- Thick layer of blubber to insulate
- Black skin underneath to absorb radiation
- Fur is hollow so creates a permanent trapped layer of air for insulation
- Hibernation to reduce activity and heat lost and also to build fat stores
What are the 2 control centres of the hypothalamus?
The heat loss centre and the heat gain centre
What happens when the body temp increases?
The heat loss centre in the hypothalamus is activated when warmer blood flows past it. It sends impulses through motor neurons in the skin and then causes effectors to produce a negative feedback response. This lowers temperature back to homeostasis
What happens when the body temp decreases?
The heat gain centre in the hypothalamus is activated when cooler blood flows past it. This then sends a signal through the nervous system to the effectors which produce responses to raise body temperature back to homeostasis.
