Thermoregulation

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Tolerance Ranges

• The best range of conditions for an organism to live in is called its optimal range.

• However, as not all animals can live in their optimal range, they can sustain life within a range of conditions (particularly temperature and water). This range is called tolerance range.

• Organisms have a preferred (optimum) niche and a marginal niche.

• Niche is the role an organism plays in its environment.

• For an organism to live outside of its optimum range, it needs to adapt to its environment (physically, psychologically and behaviourally).

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Thermoregulation

• As the temperature on earth varies a lot, organisms need to be able to regulate their own body temperature.

- Too high leads to enzymes denaturing and bodies overheating.

- Too low leads to slower metabolic activity and not being able to support the needs of the organism.

• The regulation of na organisms internal temperature is called Thermoregulation.

• Organisms can gain heat in two main ways:

1. Metabolism of food

2. Absorption of solar energy either directly or indirectly from:

- Heat radiated from objects

- Heat convected from the warming of the ground

- Heat conducted from the ground

• Organisms can lose heat from the body through

- Evaporation of water

- Conduction from body to the environment

- Convection from the body to the air or water

- Radiation from the body to the environment

Thermo-Conformers:

• Not all organisms are thermo-regulators. Some, like most fish, are thermo-conformers. A thermo-conformer does not regulate their internal body temperature but simply adopts the surrounding temperature as their own.

• Since the temperature of deep bodies of water are very stable, there is little need for its inhabitants to regulate their body temperature - especially as thermo-regulation can consume a great deal of energy.

• The temperatures of the deep ocean do not exceed 5˚C so most organisms have very low metabolism rates and are invariably slow-moving animals.

Ectotherms and Endotherms:

• Organisms use two different strategies for surviving extremes or even moderate variations of temperature.

Ectotherms (heat from outside): get their body heat mainly from the environment and can tolerate a reasonably wide range of body temperatures. These used to be called 'cold-blooded'.

Endotherms (heat from inside): get most of their heat from the metabolic processes that occur inside them. They are not so reliant on on their external environment for warmth.

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Conservation of Heat in Endotherms

• Most endotherms maintain their internal core temperature within a range of 32-45˚C. This allows metabolic enzymes to operate at their optimum rate.

• Due to movement requiring ATP production through cellular respiration (which also produces heat), animals with high energy uses also have a higher core temperature.

• The hummingbird is an excellent example, due to its high energy usage, it maintains an internal body temperature of around 40.5°C- considerably warmer than a human.

Physiological Features that Reduce Heat Loss:

• How quickly heat is lost is dependant on the difference in temperature between the animals body and its environment (temperature gradient). The bigger the temperature gradient, the faster the heat loss.

• Therefore, animals with larger SA:V ratio will lose heat faster.

• As the limbs of slender animals is a sight of heat loss, adaptions can help to reduce this.

• Physiological adaptions to reduce heat loss include:

• Restricting Arterioles: Reducing blood flow to the skin stops heat from being lost at the extremities.

• Shunt Vessels: Special vessels between arterioles and venules enable the blood to bypass the skin artilleries.

• Counter-current blood flow system: The arteries near the extremities are very close to the veins. As they flow in opposite directions, heat is exchanged between them and more heat goes back to the vital organs.

Physiological Adaptions:

• Other physiological features include:

• Erector Muscles: Hair or feathers can be raised by contraction of erector muscles which increases the thickness of the insulating layer of air trapped between the hair/feathers of the skin (goosebumps).

• Insulation: Many animals have a thick layer of insulation via fat layers just beneath the skin. As temperatures decrease, the amount of fat in the layer increases to maintain internal heat.

• Some physiological adaptions help to produce heat - called thermogenesis. Metabolism generates heat and it can be increased by:

• Increasing the contraction of muscles by moving around or shivering.

• The action of certain hormones that increase metabolic rate.

• Brown adipose tissue can be used to generate heat. It is a specialised fat tissue that is designed to produce large amounts of heat. It contains specialised mitochondria which makes little ATP but produces a lot of heat. Rodents have a lot of this.

Behavioural Adaptions:

• Behavioural adaptions to reduce heat loss include:

- Diurnal activity: moving during the day rather than at night

- Kleptothermy: Huddling in groups to share body heat and not be as exposed to the elements.

- Torpor: When food is scarce some animals drop their metabolic rate to a very low state in order to conserve energy. Hibernation is an example of long-term torpor. Many animals undergo short term torpor.

Structural Adaptions:

• Structural (physical) features also assist to prevent heat loss.

• Metabolic heat production could outstrip food supplies in an area. As such, active animals in cold climates tend to have a large torso with short extremities, to reduce the amount of heat lost through them.

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Reduction of Heat in Endotherms

Reducing Heat:

• It is often harder to lose heat than to gain it. Many adaptions to hot climates are the opposite of those in cold climates.

• Vasodilation: Increasing blood flow to the extremities to enable it to be lost to the environment. The widening of arterioles to allow blood through.

• Sweating: Glands in the skin release water to create a moisture barrier. High amounts of energy is required to turn water into steam which means a lot of the heat we produce is used up in the process. Thus, increasing heat loss.

• Panting/licking: Similar to sweating, the moisture in the saliva helps increase heat loss.

• Insulation: Hair and subcutaneous fat can help reduce the amount of heat gained from the environment. Hair erector muscles can also relax creating less of a layer of air between hair and skin.

• Fat storage: Is limited to specific areas to reduce its insulating effect and increase heat loss.

• Behavioural Mechanisms: Nocturnal activity, prolonged torpor during summer (aestivation).

• Structural Features: Such as slim torso and large extremities helps to increase heat loss. Ears are thin and have high blood flow to increase heat loss.

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Homeostatic Control of Heat

• The internal body temperature is controlled by the hypothalamus.

• Once it receives info about being too cold/hot, it starts a list of procedures to regain homeostasis.

• Also causes pituitary gland to release some hormones to aid in the process. Thyroid hormones are released which speed up or slow down metabolism to lose/gain heat.