Animals are either warm-blooded or cold-blooded
and this determines what they need to do to maintain an appropriate body temperature.
Their body temperature needs to remain within a particular range so all their
necessary biochemical reactions (i.e. digestion, respiration) can occur!
Their body temperature needs to remain within a particular range so all their
necessary biochemical reactions (i.e. digestion, respiration) can occur!
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Warm-blooded animals are called homeotherms.
Their body temperature is controlled in a way that mimics an oven - it uses a type of 'thermostat' to ensure the temperature remains within a narrow range, if the temperature drops too low the oven will heat itself back up, if the temperature is too hot the oven will reduce the heat Because the source of heat comes from within the animal, they are referred to as endotherms (endo = internal) Cold-blooded animals are called poikilotherms.
Their body temperature is controlled by the external environment - so if it is warm outside the animal's body temperature will be warm, if it is cold outside the animal's body temperature will be cold. These animals have particular behaviours they perform to ensure the change in temperature is reduced Because the source of heat comes from the external environment, these animals are referred to as ectotherms (ecto = external) |
Regardless of whether an animal is an endotherm or ectotherm.. they must be able to regulate their body temperatures, because of...
If the temperature is too high, it will exceed the optimum temperature at which enzymes can catalyze particular reactions. When the temperature is too high, it breaks the bonds holding the protein (enzyme) in its shape, and this means it will become deformed. This is also called denaturing. If an enzyme is denatured, the substrate (thing that it is reacting) won't be able to fit inside the active site of the enzyme, and the reaction won't be able to take place! If important reactions within our body can't take place, we are screwed!
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If the temperature is too low, it will mean that the enzymes are not working very quickly and this can actually be very bad for an organism! The reactions necessary for living will be occurring too slowly and the animal will not be able to function! For example, if reactions like digestion are occurring too slowly, the body isn't getting enough nutrients to carry out other reactions and the body will start to shut down!
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Sources of heat
Heat can be produced or passed on
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Heat production
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Heat being 'passed on'
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aka. Thermogenesis
Heat is produced via exothermic reactions. These are reactions that, when they occur, give off heat as a by-product. Two of the main exothermic reactions that occur are digestion and respiration - both of these give off heat. These reactions occur mainly in the intestines, liver, heart and brain.
When these reactions are occurring normally, such as when we are sleeping or doing 'not much', they create what is referred to as the basal metabolic rate (BMR) - the rate which these reaction occurs when there is no stress put on the body. When we exercise, for example, more stress is put on the body and this increases our BMR, making us heat up. Another example is when we (or other animals) have a 'fight or flight' response, we heat up. You might notice this when you get a shock or fright from something, you feel hot! This is due to adrenaline being released, which also increases our BMR!
When these reactions are occurring normally, such as when we are sleeping or doing 'not much', they create what is referred to as the basal metabolic rate (BMR) - the rate which these reaction occurs when there is no stress put on the body. When we exercise, for example, more stress is put on the body and this increases our BMR, making us heat up. Another example is when we (or other animals) have a 'fight or flight' response, we heat up. You might notice this when you get a shock or fright from something, you feel hot! This is due to adrenaline being released, which also increases our BMR!
via. Energy transfer
Heat can be gained (and lost) through the following 4 processes:
- Conduction - if a warm surface came into contact with a colder surface, heat from the warmer surface would be conducted to the colder surface. The warmer surface would 'lose heat' and cool down, as it is, effectively, giving some heat energy away. The same goes for the opposite - if a warm surface came into contact with a hotter surface, heat from the hotter surface would be conducted to the warm surface. The warm surface would 'gain heat' and warm up.
- Convection - in humans, heat is lost via convection - air that moves across the surface of the skin picks up the warm 'insulating' air around the skin, and takes it away. This helps cool us down but can be bad if we are cold and trying to warm up!
- Evaporation - warmth produced by us can be evaporated with any moisture we produce; sweat, vapor in our lungs, etc.
- Radiation - warm objects emit heat, cooling them down. By being close to a warm object we are able to heat up by absorbing the radiant heat.
Sweating is a form of evaporative cooling
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Some lizards, such as the Namib lizard, stand on two legs (not four) to reduce the amount of heat conducted from the hot desert ground to their bodies, reducing heat uptake
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Some animals have a thick layer of hair, fur or wool. This traps air close to their body which acts as a layer of insulation, keeping them warm
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Bumblebees shiver in order to heat up their flight muscles. Their thick fluffy fuzz layer traps the heat and keeps it close, conserving it
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Many animals in colder climates, such as the musk oxen, huddle together to retain body heat
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Dogs stick their tongues out to cool down, by way of evaporative cooling
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Thermoregulation in humans
1.Environmental change detected by receptors in the skin and internal organs (such as bladder)
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2.'Stimuli' message taken via nerves to hypothalamus, which is the control centre
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3.Hypothalamus decides on appropriate response and send message to effectors, telling them to produce a response via the nervous (nerves) and/or endocrine (hormones) systems
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Heat loss is detected by thermoreceptors , which are found in both the skin (lots in our torso area) and in our internal organs. These receptors create a 'heat loss message' which is sent via the nervous system (synapses between nerve cells / neurons) to hypothalamus (thermostat in the brain). The 'heat loss message' arrives at hypothalamus and it responds by coordinating a response for the body to both generate and conserve heat. The communication between the hypothalamus (control centre) and effectors (skin, muscles, glands) involves the nervous system and the endocrine system.
The change in temperature is a deviation from normal - the body will immediately try and correct this deviation. This makes thermoregulation an example of the negative feedback loop. |
Factors that cause heat loss:
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The rate at which heat is lost increases with wind chill it accelerates heat loss via conduction. Heat loss occurs when the body and environment are different temperatures; if it is colder around the body the heat from the body will be lost. Things like being wet, inactive, dehydrated, in shock or wearing not many clothes can cause heat to be lost. |
NS responseThe hypothalamus sends a message back to the skin, telling the piloerector muscles of the hairs to contract, causing the hairs to stick up. This traps air close to the skin's surface, creating a layer of insulation. This reduces heat loss.
The hypothalamus also sends a message via the nerves to our skeletal muscles, promoting increased contractions, causing us to shiver. This produces internal heat as the rate of respiration increases (increasing the BMR). |
ES responseThe hypothalamus tells the thyroid gland (in the neck) to release a hormone called thyroxine. When released, thyroxine increases the BMR, allowing more heat to be produced; helping the body to warm back up.
The hypothalamus tells the body to release nor-adrenaline which causes blood vessels to constrict. This is called vasoconstriction. This reduces blood flow to places where heat can be easily lost, such as arms and legs, and keeps blood close to the core. This reduces heat loss. |
When the body has returned back to within the safe temperature range, this will signal to the receptors that the disruption is over. The response will stop. This is negative feedback.
Heat gain is detected by thermoreceptors , which are found in both the skin (lots in our torso area) and in our internal organs. These receptors create a 'heat gain message' which is sent via the nervous system (synapses between nerve cells / neurons) to hypothalamus (thermostat in the brain). The 'heat gain message' arrives at hypothalamus and it responds by coordinating a response for the body to both reduce heat production and lose heat. The communication between the hypothalamus (control centre) and effectors (skin, muscles, glands) involves the nervous system and the endocrine system.
The change in temperature is a deviation from normal - the body will immediately try and correct this deviation. This makes thermoregulation an example of the negative feedback loop. |
Factors that cause heat gain:
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Heat can be gained directly from the sun, or surrounding environment through conduction and radiation. Having layers of fat creates insulation, making it harder for heat that is generated by activity to be lost from the body. Intense exercising causes heat to be produced by the body, and with excessive clothing it is maintained close to the body, increasing heat gain. |
NS responseThe hypothalamus sends a message back to the skin, telling the piloerector muscles of the hairs to relax, flattening the hairs. This stops air from being trapped close to the skin (when it is, it acts as a layer of insulation). Without the insulation, heat loss is increased.
The hypothalamus also sends a message via the nerves to the eccrine sweat gland (sweat glands in the skin), telling them to produce sweat. Sweat is mostly water, and some salts, originating from our blood. Taking the warm liquid from blood and moving it to the outside of the body for it to be lost via evaporation. This increases heat loss. |
ES responseThe hypothalamus tells the thyroid gland (in the neck) to stop releasing thyroxine, therefore reducing the BMR, allowing less heat to be produced; stopping the body from getting too hot.
The hypothalamus tells the body to release adrenaline which causes blood vessels to expand/dilate. This is called vasodilation. This increases blood flow to places where heat can be easily lost, such as arms and legs, increasing heat loss. |
When the body has returned back to within the safe temperature range, this will signal to the receptors that the disruption is over. The response will stop. This is negative feedback.
Possible breakdowns
When the body cannot restore the body's temperature back to equilibrium without help
Hypothermia
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Causes
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Symptoms
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Treatment
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Risk factors
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of Mild Hypothermia - Shivering. Vasoconstriction reduces blood flow to extremities to reduce heat loss.
of Moderate Hypothermia - Slow movements, loss of muscle co-ordination. Vasoconstriction increases, causing extremities to turn a blue colour - ears, fingers, nose, toes. The start of mental confusion also may begin.
of Severe Hypothermia - Become irrational, speech slows, may enter unconsciousness. Eventually organs and heart fail, causing death.
of Moderate Hypothermia - Slow movements, loss of muscle co-ordination. Vasoconstriction increases, causing extremities to turn a blue colour - ears, fingers, nose, toes. The start of mental confusion also may begin.
of Severe Hypothermia - Become irrational, speech slows, may enter unconsciousness. Eventually organs and heart fail, causing death.
Slow re-warming is necessary. If heat is applied too quickly to the hypothermic person, their body may attempt to remove sudden excess of heat and this will cause more heat loss and possibly death.
for Mild Hypothermia - passive rewarming - get them in some warm, dry clothes and in a warm, dry environment. Allow their own body heat to slowly warm them back up. for Moderate Hypothermia - active external rewarming - this requires some sort of 'warming device', this could be a hot water bottle or a warm bath. for Severe Hypothermia - active internal rewarming - this requires warmth to be internally given; via warm intravenous fluids or inhaling warm moist air. |
- Age - very young and very old people are at a higher risk of developing hypothermia as they have poor muscle tone and less brain control over their physiological responses
- Mental status - conditions such as Alzheimer's can result in a person being exposed to an environmental condition that results in hypothermia
- Drug or alcohol abuse - the impaired judgement that results from substance abuse increases the occurrence of 'risky behaviour', making it more likely the individual may put themselves in a compromising situation. Alcohol is also known to interfere with the body's shivering response and it increases vasodilation
- Certain medications - some medications affect the shivering response
- Medical conditions - conditions that affect the production of thyroxine or adrenaline, or that affect the hypothalamus or thermoreceptors, will interfere with the body's ability to thermoregulate
Hyperthermia
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Causes
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Symptoms
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Treatment
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Risk factors
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of Phase 1 Hyperthermia - Overexertion - short and rapid breathing, flushed red face.
of Phase 2 Hyperthermia - Heat exhaustion - dry mouth, nausea, profuse sweating and cramps. Skin appears red due to blood being directed there (vasodilation) to reduce core temperature.
of Phase 3 Hyperthermia - Heat stroke - sweat no longer produced, skin becomes hot and dry. Individual becomes disorientated, may collapse, become unconscious. Enzymes denature, slowing metabolic processes. Death follows!
of Phase 2 Hyperthermia - Heat exhaustion - dry mouth, nausea, profuse sweating and cramps. Skin appears red due to blood being directed there (vasodilation) to reduce core temperature.
of Phase 3 Hyperthermia - Heat stroke - sweat no longer produced, skin becomes hot and dry. Individual becomes disorientated, may collapse, become unconscious. Enzymes denature, slowing metabolic processes. Death follows!
Rapid lowering of core body temperature is necessary, but this can't happen too quickly otherwise the body will respond to the colder temperature by shivering and vasoconstriction, reducing heat loss and making hyperthermia worse.
for Phase 1 Hyperthermia - external treatment - seek shade and drink plenty of fluid for Phase 2 Hyperthermia - external treatment - same as phase 1, applying ice packs on the skin, sponging the body with cool water, using cool blankets. for Phase 3 Hyperthermia - internal treatment - this requires cool intravenous fluids to be administered or flushing the stomach or rectum with cold water. |
- Age - very young and very old people are not as good at sweating, nor can they effectively carry out voluntary responses (i.e. make a decision to do something) to reduce body temperature
- Obesity - these people have a decreased SA:V ratio, making it harder for heat to be lost; over-exertion may lead to a stroke or hyperthermia in these people
- Insulative clothing - i.e. what firefighters wear, traps the warm air close to the body and does not let sweat evaporate, making the individual unable to increase heat loss
- Certain medications - such as diuretics, anti-psychotics, vasoconstrictors - which may reduce vasodilation as well as sweating