Thermoregulation In Endotherms

What are endotherms?

Animals that rely on metabolic processes to maintain a constant body temperature.

What is needed to detect a change?

Receptors.

Where are peripheral temperature receptors located?

In the skin, and detect the temperature of the blood deep in the body.

What is the temperature of the skin most likely to be affected by?

External conditions, rather than the hypothalamus.

What does the combination of receptors and the hypothalamus give the body?

Great sensitivity and allows it to respond not only to actual changes in the temperature of the blood, but to pre-empt possible problems that might result from changes in the external environment.

What do the temperature receptors in the hypothalamus act as?

The thermostat of the body, controlling the responses that maintain the core temperature in a dynamic equilibrium.

What do endotherms use their internal exothermic activities to do?

Keep them warm.

What do endotherms use energy-requiring physiological responses to do?

Cool them down. They also have passive ways of heating up and cooling down,

What are the behavioural responses that both ectotherms and endotherms have in response to temperature changes?

• Basking in the sun.

• Becoming dormant in the cold seasons (hibernation).

• Pressing themselves to warm/cool surfaces.

What are some of the additional behavioural responses humans have to help control body temperature?

Clothes are worn to stay worm, houses are built, and then heated up or cooled down to maintain the ideal temperature.

In spite of behavioural responses, what do endotherms mainly rely on?

Physiologicla adaptations.

What do the physiological adaptations of endotherms include?

• The peripheral temperature receptors.

• The thermoregulatory centres of the hypothalamus.

• The skin.

• Muscles.

What are the different responses endotherms have in place when cooling down?

• Vasodilation.

• Increased sweating.

• Reducing the effect of hair or feathers.

When temperature rises, what happens to the arterioles near the surface of the skin?

They dilate (vasodilation). The vessels that provide a direct connection between the arterioles and venules constrict.

What is the result of the dilating of the arterioles near the skin and the constriction of the vessels connecting the arterioles and venules?

Blood is forced 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, where does the cooling result from?

Conduction.

What happens to sweating rates as temperature increases?

It also increases. Sweat spreads out across the surface of the skin. In some mammals, there are sweat glands all over the body.

What happens as sweat evaporates from the surface of the skin?

Heat is lost, cooling the blood below the surface.

What happens in animals where sweat glands are restricted to the non-hairy parts of their body (like dogs)?

These animals often open their mouths and pant when they get hot, losing heat as the water evaporates.

What happens to the erector pili (the hair erector muscles) as body temperature increases?

They 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.

What do endotherms that live in hot climates often have?

Anatomical adaptations as well. These minimise the effect of high temperatures and maximise the ability of the animal to cool down through the surface area of the body.

What are examples of anatomical adaptations for cooling down?

• A large SA:V to maximise cooling.

• Pale fur.

• Feathers to reflect radiation.

What are the different responses in place when an endotherm needs to warm up?

• Vasoconstriction.

• Decreased sweating.

• Rising body hair or feathers.

• Shivering.

What happens in vasoconstriction?

The arterioles near the surface of the skin contract and the vessels connecting the arterioles and venules dilate, so little blood flows through the capillary networks close to the surface of the skin.

What is the effect of the constriction of the arterioles near the surface of the skin and the dilating of the vessels connecting the arterioles and venules?

The skin looks pale, and very little radiation takes place. The warm blood is kept well below the surface.

As the core temperature falls, what happens to the sweating rate?

Rates of sweating decrease and sweat production will stop entirely. This greatly reduces cooling by the evaporation of water from the skin.

As the body temperature falls, what happens to the erector pili muscles?

They contract, pulling the hair or feathers of the animal erect. This traps an insulating later of air and so reduces cooling through the skin. This has little effect in humans.

As the core temperature falls, what may the body begin to do?

Shiver.

What is shivering?

The rapid, involuntary contracting and relaxing of the large voluntary muscles in the body. The metabolic heat from the exothermic reactions warms up the body instead of moving it.

What additional anatomical adaptions may endotherms in cold climates have?

• Minimal SA:V to reduce cooling.

• A thick layer of insulating fat underneath the skin.

• Hibernation.

What are the physiological responses of endotherms to changes in the core temperature the result of?

Complex homeostatic mechanisms involving negative feedback control from the hypothalamus. There are two centres.

What ate the two centres of the thermoregulatory centre?

• The heat loss centre.

• The heat gain centre.

When is the heat loss centre activated?

When the temperature of the blood flowing through the hypothalamus increases.

When is the heat gain centre activated?

When the temperature of the blood flowing through the hypothalamus decreases.