chapter 15 p2 Flashcards
Principles of thermoregulation in endotherms:
- Endotherms use their internal exothermic metabolic activities to keep them warm, and energy-requiring physiological responses to help them cool down.
- They also have passive ways of heating up and cooling down, to reduce the energy demands on their bodies.
behavioural responses for thermoregulation in endotherms:
- basking in the Sun, pressing themselves to warm surfaces, wallowing in water and mud to cool down, and digging burrows to keep warm or cool.
- Some animals even become dormant through the coldest weather (hibernation) or through the hottest weather (aestivation is a period of prolonged or deep sleep similar to hibernation but occurs in summer or during dry seasons to avoid heat stress rather than cold).
- Humans have additional behavioural adaptations to help control body temperature - clothes are worn to stay warm, houses are built, and then heated up or cooled down to maintain the ideal temperature.
however, endotherms still what?
- In spite of these behavioural responses, endotherms mainly rely on physiological adaptations to maintain a stable core body temperature, regardless of the environmental conditions or the amount of exercise being done.
- These adaptations include the peripheral temperature receptors, the thermoregulatory centres of the hypothalamus, the skin, and muscles.
Cooling down:
If the core body temperature increases it is important for an animal to cool down.
There are a number of rapid responses to a rise in the core temperature that are common to all endotherms. These include:
Vasodilation:
Increased sweating:
Reducing the insulating effect of hair or feathers:
Vasodilation:
- The arterioles near the surface of the skin dilate when the temperature rises.
- The vessels that provide a direct connection between the arterioles and the venules (the arteriovenous shunt vessels) constrict.
- This forces blood through the capillary networks close to the surface of the skin.
- The skin flushes, and cools as a result of increased radiation.
- If the skin is pressed against cool surfaces, then the cooling results from conduction.
diagram of vasodilation
Increased sweating:
- As the core temperature starts to increase, rates of sweating also increase.
- Sweat spreads out across the surface of the skin.
- In some mammals, including humans and horses, there are sweat glands all over the body.
- As the sweat evaporates from the surface of the skin, heat is lost, cooling the blood below the surface.
- In some animals, the sweat glands are restricted to the less hairy areas of the body such as the paws.
- These animals often open their mouths and pant when they get hot, again losing heat as the water evaporates.
- In human beings, around 1 dm’ of sweat is lost by evaporation on a normal day.
- If the conditions are very hot and dry or the person is exercising very hard, up to 12 dm of sweat a day can be lost.
- Kangaroos and cats often lick their front legs to keep cool in high temperatures.
Reducing the insulating effect of hair or feathers:
- As the body temperature begins to increase, the erector pili muscles (the hair erector muscles) in the skin relax - as a result, the hair or feathers of the animal lie flat to the skin.
- This avoids trapping an insulating layer of air - It has little effect in humans.
- Endotherms that live in hot climates often have anatomical adaptations as well as the behavioural and physiological adaptations already described.
- These minimise the effect of high temperatures and maximise the ability of the animal to cool down through the surface area of the body.
- They include a relatively large surface area: volume (SA:V) ratio to maximise cooling (e.g., include large ears and wrinkly skin), and pale fur or feathers to reflect radiation.
Warming up in endotherms
If the core temperature falls it is important for an animal to warm up and prevent further cooling.
There are a number of rapid responses to a fall in the core temperature that are common to all endotherms.
Vasoconstriction:
Decreased sweating:
Raising the body hair or feathers:
Shivering:
Vasoconstriction:
The arterioles near the surface of the skin constrict.
The arteriovenous shunt vessels dilate, so very little blood flows through the capillary networks close to the surface of the skin.
The skin looks pale, and very little radiation takes place.
The warm blood is kept well below the surface.
Vasoconstriction diagram
Decreased sweating:
As the core temperature falls, rates of sweating decrease and sweat production will stop entirely.
This greatly reduces cooling by the evaporation of water from the surface of the skin, although some evaporation from the lungs still continues.
Raising the body hair or feathers:
As the body temperature falls, the erector pili muscles in the skin contract, pulling the hair or feathers of the animal erect.
This traps an insulating layer of air and so reduces cooling through the skin.
The effect can be quite dramatic and it is a very effective way to reduce heat loss to the environment in many animals.
In humans this has little effect although you can observe the hairs being pulled upright.
Shivering:
- As the core temperature falls the body may begin to shiver.
- This is the rapid, involuntary contracting and relaxing of the large voluntary muscles in the body.
- The metabolic heat from the exothermic reactions warm up the body instead of moving it and is an effective way of raising the core temperature.
Endotherms living in cold climates often have additional anatomical adaptations to help them keep warm.
- Many have adaptations that minimise their SA: V ratio to reduce cooling (e.g., small ears).
- Another common adaptation is a thick layer of insulating fat underneath the skin, for example, blubber in whales and seals.
- Some animals hibernate - they build up fat stores, build a well-insulated shelter, and lower their metabolic rate so they pass the worst of the cold weather in a deep sleep-like state.
diagram of Controlling thermoregulation:
