lecture 23 - body temperature and thermoregulation Flashcards
What is an endotherm?
Body temperature depends on internal heat production by animal - produces its own heat - “warm blooded”.
What is an ectotherm?
Body temperature depends on heat acquired from the environment - “cold blooded”.
Warm and cold blooded is not entirely accurate, as a “cold blooded” ectotherm may have warmer blood than an endotherm in a hot environment.
What is a homeotherm?
Body temperature constant (usually as a result of endothermy but also some ectotherms if the environment it lives in has a constant temperature) - when temperature isn’t constant, this can be very harmful.
What is a polikotherm?
Body temperature variable and strongly influenced by environment - ectotherms.
Describe endotherms
Mammals and birds are examples of endotherms. Heat derived from metabolism as a byproduct of breaking down substrates to produce metabolism. Makes living on land feasible due to the huge range of temperatures on earth. Allows a high level of activity as all animals have an optimal temperature range to allow reactions in the body - regulation of body temperature means reactions continue all the time, despite environmental temperature. Energetically expensive (requires high energy intake) as you need to break down substrates to produce heat as a byproduct. Adapted to achieve thermoregulation - e.g. conserve energy so less energy is required.
Describe ectotherms
Reptiles, amphibians and most fish are examples of ectotherms
Very small contribution of metabolism to temperature, so don’t rely on this but instead gain their heat from the outside environment.
Lower metabolic rate and food intake (and therefore typically less active) as it doesn’t contribute significantly to heat production, and also because outside temperature isn’t always constant or optimum.
Adapted to achieve thermoregulation, but this is mainly behavioural (e.g. moving to somewhere warm).
Describe the relationship between size and metabolic rate
The bigger the animal, the higher the metabolic rate, in general.
At every body mass, endotherms always have a higher metabolic rate than ectotherms - they have to break down more substrate to maintain their body temperature.
Describe mechanisms of heat loss
Conduction: transfer of heat directly from surface to the body when they touch.
Convection: transfer of heat from the movement of air or water over the body surface.
Radiation: a surface that is hotter than absolute zero will lose heat via electromagnetic waves - body loses heat this way, but the sun gives off heat this way, heating the body.
Evaporation: loss of heat from a wet surface as water evaporates.
What is thermoregulation?
how the body is adapted to keep heat in the body when its cold and lose heat when its hot
What is body insulation?
a covering on outside surface to keep internal heat production inside the body - prevents heat loss (hair, feathers, subcutaneous fat etc). Muscles are quite a poor insulator, which is why insulation is required, whereas fur is a much better insulator, as it traps a layer of air and air is an excellent insulator.
HOWEVER, when fur gets wet it loses its ability to trap air and therefore loses its insulating properties. Animals in water therefore use blubber (a thick layer of subcutaneous fat) to maintain body temperature in cold water. However, fur is 6x more effective than blubber so animals require a lot of blubber.
Describe adaptations to the circulatory system
Constriction of vessels to skin reduces heat loss by reducing blood-flow to the body surface OR dilation of vessels to skin increases blood flow and heat lost. Cold temperature is detected by the hypothalamus, which responds by telling the autonomic nervous system to constrict the blood vessels that are supplying the superficial vessels near the skin surface. This keeps the heat within the body.
The opposite is true if its really hot, resulting in dilation of vessels.
Another example: Countercurrent heat exchanger seen in dolphins, ducks etc. When vessels run in opposite orientation to each other, particularly when going to extremities such as fins. As blood moves towards the extremities, they lose heat but as the cold blood returns to the core body, it warms up the whole way as to not cool down the core body temperature.
What is evaporative heat loss?
Heat lost across surface of skin - humans do this by sweating, which is again controlled by the hypothalamus. Most animals can’t sweat and so pant instead - they expose more of their moist surfaces to the environment, which they lose heat from via evaporation. These are both involuntary actions.
Elephants can also take advantage of evaporative heat loss by spraying water on themselves, while other animals lick themselves.
What are behavioural changes that prevent heat loss?
Usually seen in ectotherms - e.g. lizards bask in the sun (and so do birds to lower activity).
Penguins and rabbits (and also evidence of bees) huddle together to prevent heat loss to the environment. Animals can also burrow and huddle in a shelter to either escape the cold or escape the full heat of the sun.
How do organisms change the rate of metabolism?
Increase movement to work body which requires more energy, and so more substrate must be broken down, producing more heat as a byproduct. Shivering is small muscle contractions which is subconscious and produces heat, as substrates must be broken down to fuel these contractions, producing heat as a byproduct.
Non-shivering thermogenesis is also subconscious and occurs in brown fat tissue - uncoupling proteins sit in the membrane of the mitochondria and reducing the proton gradient for ATP production - makes ATP less efficient so you’ll have to burn more substrate (and generate more heat) for the same amount of ATP.
What is facultative endothermy?
Ectotherms can sometimes temporarily display endotherm behaviour.
Temporarily increase body temperature above environmental by exercise
Examples include the bumblebee, some moths and female pythons
Heat achieved by contraction of antagonistic flight muscles in bumblebees and moths - maintain body temperature during flight - like shivering.
Shivering thermogenesis in pythons when they are brooding their eggs to ensure they are exposed to an optimum environmental temperature.
