Body Temperature Regulation

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Body Temperature

The body temperature is always measured in the mouth in an adult because this is the core temperature (the temperature of the head and trunk) therefore the temperature at which the vital organs like the brain, heart and lungs must be maintained. The body generates heat by chemical reactions taking place in the cells such as respiration. 

Five ways in which heat is lost from the body: 

  • Expired air
  • Faeces/urine/excretion
  • Conduction
  • Convection
  • Radiation 

The two physical features that affect the rate at which heat is lost from the body are: 

  • The thickness of the layer of the fat under the skin 
  • The surface area to volume ratio (tall, thin people have a bigger surface area than small, chunky people) 
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The Control of Body Temperature

Normally body temperature is regulated by homeostasis (maintaining a constant internal environment e.g. maintaining a constant body temperature) 

Body temperature is controlled and regulated by the nervous system, the circulatory system and the skin. The 3 structures which are important in temperature regulation are: blood capillaries, sweat glands and body hairs. 

When the body temperature rises, this is detected by two types of receptor in the body: 

  • Temperature receptors in the skin
  • Hypothalamus in the brain

The body responds by putting various mechanisms in place such as: 

  • Vasodilation - which is when blood is diverted to the capillaries in the surface of the skin. This helps the body to lose heat because this means that more blood flows nearer to the skin surface. This increases heat loss by radiation. 
  • Sweating - this means that water in sweat evaporates. Heat is lost during this evaporation. 
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The Control of Body Temperature (2)

After excessive sweating dehydration can occur which causes less heat to be lost from the skin because there is less blood volume which means there is less water in the blood. Therefore the body sweats less. Heat would normally be lost due to sweating as the liquid produced through sweating is lost through evaporation. Evaporation would normally produce cooling but this doesn't happen. 

Dehydration can also cause a rise in temperature because there is a reduced blood volume so the heart has to work harder to pump the blood around the body. This generates even more heat. When a person is dehydrated their blood pressure goes down because there is less water in the blood so the volume of the blood is less. 

A person could suffer from heat stroke and exhaustion if they have been sweating profusely but the fluids lost by sweating have not been replaced so the person becomes dehydrated. 

The body's response to infection is to produce a high temperature or fever. The rise in body temperature can help recovery. This increase in body temperature helps to kill bacteria. This lessens the infections. 

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The Control of Body Temperature (3)

When the body temperature falls this is detected by two types of receptors: 

  • Temperature receptors in the skin
  • Hypothalamus in the brain

Various mechanisms are then put in place: 

  • Vasoconstriction - when blood is diverted awat from the skin surface and towards the body's core. This helps to prevent any further loss of heat from the body because less heat is lost from the skin by radiation
  • Shivering - this is rapid muscle contractions which generate waste heat from chemical energy. 
  • Body hair - hairs on skin become erect. This traps air in between the hairs. The air acts as an insulating layer
  • Hypothermia - this is when the core body temperature drops to 32 degrees celsius. Symptoms are: pale dry skin, slow pulse rate, shivering, fainting, lack of coordination/confusion/tiredness 
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Mechanisms to counteract overheating

Temperature receptors in the skin and the hypothalamus detect a rise in body temperature

Muscles in arterioles relax, causing vasodilation

Blood is diverted to the skin surface and heat is lost through radiation

Sweating occurs

Water in sweat evaporated from the skin surface, removing heat energy and causing a cooling effect 

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Mechanisms to counteract heat loss

Temperature receptors in the skin and the hypothalamus detect a fall in body temperature

Muscles in arterioles contract, causing vasoconstriction

Blood is diverted away from the skin surface and less heat is lost by radiation

Muscles contract rapidly (shivering) , releasing waste heat energy from chemical reactions (respiration)

Piloerection occurs and body hairs stand on end

This traps a layer of air next to the skin, acting as an insulator and reducing heat loss by convection. 

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