7.2 Flashcards
Radiation is when heat energy is transferred from one place to another as
Electromagnetic waves
3 ways in which the body gains or loses heat:
- radiation
- conduction
- convection
Conduction is in which heat energy is transferred by the collisions of
Molecules
Solids and liquids conduct heat better than air
Convection is in which heat is transferred by
Currents in air or water
The body also loses heat by
Evaporation of sweat
(Evaporation) when water in sweat turns from liquid into vapour, it takes heat from the
Body
Heat is also lost in substances that leave the body, such as:
Urine
Faeces
Exhaled air
Human body temperature is controlled by the
Hypothalamus in the brain
Sensory receptors in the brain, called thermoreceptors, monitor the temperature of the blood
Flowing through the hypothalamus (known as core body temperature)
Thermoreceptors are also in the skin which monitor skin temperature. These thermoreceptors send nerve impulses to the
Hypothalamus
If the thermoreceptors in the hypothalamus detect a change in body temperature away from the normal level, the hypothalamus brings about
Corrective mechanisms
Responses are split into:
Heat loss
Heat conservation
If the thermoreceptors in the hypothalamus detect an increase in body temperature, the hypothalamus corrects this by bringing about:
Heat loss responses
Heat loss responses include:
Vasodilation
Increased rate of sweating
Pilorelaxation
(HLR) vasodilation occurs by;
- Hypothalamus sends impulses along the parasympathetic nerves to the skin arterioles
- Smooth muscle in the walls of these arterioles relax
- Shunt vessel constricts, forcing more blood to flow through the surface capillaries
(HLR) vasodilation causes an increase in the amount of energy lost by
Radiation
(HLR) increased rate of sweating occurs by more sweat being secreted on to the surface of the skin. As the water on the skin evaporates it
Removes heat from the body
(HLR) pilorelaxation has little effect in modern humans as we do not have hairy skins. However the parasympathetic nerves going to the wrecker pilli muscles at the base of the skin hairs causes these muscles to relax. This means that the hairs
Lie flat
- less air is trapped next to the skin
- reduces the insulating effect of the body hair
Humans also reduce their body temperature by:
Behavioural responses - opening a window
Behavioural responses as the thermoreceptors in the skin and hypothalamus send impulses to the cerebral cortex in the brain. This makes the person aware that they are too hot. As a result, they do something to help cool down.
People also become more inactive when they are too hot. This helps to reduce body temperature as the rate of respiration in muscle tissue decreases. This means that
Less heat is produced
if a person is exposed to high temperatures for a long period of time, the body produces less
Thyroxine
Thyroxine is a hormone that increases metabolic rate. As a result of being less produced in high temperatures the metabolic rate is
Reduced
If the thermoreceptors in the hypothalamus detect a decrease in body temperature, the hypothalamus corrects this by bringing about
Heat conservation responses
Heat conservation responses include:
- vasoconstriction
- decreased rate of sweating
- piloerection
(HCR) vasoconstriction- the hypothalamus sends impulses along the sympathetic nerves to the skin arterioles, causing
- smooth muscles in the walls of arterioles to contract
- the shunt vessel relaxes(forcing less blood to flow through the surface capillaries)
(HCR) effect of vasoconstriction is it reduces the amount of
Heat energy lost by radiation
(HCR) decreased rate of sweating, less sweet is secreted in to the surface of the skin, so less heat energy from the body is:
Used to evaporate the water in the sweat into vapour
(HCR) piloerection - although this has very little effect in humans, the erector pili muscles attached to the hairs in the skin pull the hairs ‘on end’ this traps an
Insulating layer of air, reducing heat loss
(HCR) behavioural responses also help to conserve heat, such as
Putting on a jumper
(HCR) shivering also generates heat. This is an involuntary response that occurs when:
-skeletal muscle contract and relax rapidly
(HCR) shivering increases the rate of respiration in muscles, so more heat is
Generated
(HCR) the hormone adrenaline is released, which
Increases the metabolic rate
(HCR) if a person is exposed to cold temperatures for long, the body produces more thyroxine - which
Increases metabolic rate
