Edexcel IGCSE Biology: Double Science 复习笔记 2.10.10 Temperature Regulation

Edexcel IGCSE Biology: Double Science 复习笔记 2.10.10 Temperature Regulation

The Role of Skin in Temperature Regulation

 

  • The skin is our largest sense organ
  • It contains many different receptors that enable us to detect various external stimuli, including touch, pressure, pain, heat and cold
  • Structures within the skin also play an important role in regulating body temperature (an example of homeostasis)

 

A-cross-section-of-human-skin

 

Human skin contains structures involved in processes that can increase or reduce heat loss to the surroundings

 

 

 

Cooling mechanisms in humans

  • Vasodilation of skin capillaries
    • Heat exchange (both during warming and cooling) occurs at the body's surface as this is where the blood comes into closest proximity to the environment
    • One way to increase heat loss is to supply the capillaries in the skin with a greater volume of blood, which then loses heat to the environment via radiation
    • Arterioles (small vessels that connect arteries to capillaries) have muscles in their walls that can relax or contract to allow more or less blood to flow through them
    • During vasodilation, these muscles relax, causing the arterioles near the skin to dilate and allowing more blood to flow through capillaries
    • This is why pale-skinned people go red when they are hot

     

  • Sweating
    • Sweat is secreted by sweat glands
    • This cools the skin by evaporation which uses heat energy from the body to convert liquid water into water vapour

     

  • Flattening of hairs
    • The hair erector muscles in the skin relax, causing hairs to lie flat
    • This stops them from forming an insulating layer by trapping air and allows air to circulate over skin and heat to leave by radiation

     

 

 

Responses-in-the-skin-when-hot

 

Responses in the skin when the body temperature is too high and needs to decrease

 

 

 

Warming mechanisms in humans

  • Vasoconstriction of skin capillaries
    • One way to decrease heat loss is to supply the capillaries in the skin with a smaller volume of blood, minimising the loss of heat to the environment via radiation
    • During vasoconstriction, the muscles in the arteriole walls contract, causing the arterioles near the skin to constrict and allowing less blood to flow through capillaries
    • Vasoconstriction is not, strictly speaking, a 'warming' mechanism as it does not raise the temperature of the blood but instead reduces heat loss from the blood as it flows through the skin

     

  • Shivering
    • This is a reflex action in response to a decrease in core body temperature
    • Muscles contract in a rapid and regular manner
    • The metabolic reactions required to power this shivering generate sufficient heat to warm the blood and raise the core body temperature

     

  • Erection of hairs
    • The hair erector muscles in the skin contract, causing hairs to stand on end
    • This forms an insulating layer over the skin's surface by trapping air between the hairs and stops heat from being lost by radiation

     

 

Responses-in-skin-when-cold

 

Responses in the skin when body temperature is too low and needs to increase

 

 

 

  • The core body temperature of humans is kept close to 37°C
    • This is very tightly controlled as a change in core body temperature of more than 2°C can be fatal

     

  • For this reason, the human body must be able to make a coordinated response to any rise or fall in body temperature
  • Temperature receptors (also known as thermoreceptors) in the skin and hypothalamus (a part of the brain) can detect minute changes in body temperature
  • The brain then coordinates a cooling or heating response, depending on what is required

 

 

Regulating-body-temperature

 

Remember - homeostasis involves the maintenance of a constant internal environment; temperature regulation is an example of homeostasis

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