4.3 - Coordination and response in living organisms
Homeostasis (體內平衡)
● ***Maintenance/control (of fluctuations) of constant internal environment in body of
organism
● ***Internal environment: includes factors, e.g.: water content of body fluids, body
temperature, pH, blood glucose levels
● This internal environment must be kept carefully within certain narrow limits, to keep
organism healthy — if limits exceeded, organism may die
Control of body temperature in humans
● Change in body temperature → effect on enzymes and their response to changes
in temperature
● ***Core body temperature: that of blood circulating around body organs; kept close
to 37˚C
● When taking part in physical activity, active muscles respire more glucose providing
energy for muscle contraction; respiration releases heat as by-product →
blood carries away heat from internal organs to body surface (skin) → heat
lost to surroundings
● Temperature receptors and their role (involving sweat glands, skin
blood vessels, skin hairs)
○ Sweating
■ Sweat - watery fluid, containing some mineral salts (including NaCl)
and urea (trace amounts)
■ ***Sweat glands draw water out from blood capillaries under skin, then
sweat passes up sweat duct to skin surface
■ Liquid evaporates from skin surface, and to do this, heat
taken from skin → causes cooling
■ If humid, sweat does not evaporate easily, therefore feels
uncomfortable (as less cooling)
○ Skin blood vessels
■ Contribute to temperature control by changing blood volume which
flows near skin surface
■ When body temperature ↑, arterioles expand; allowing more
blood flow through blood capillaries near skin surface
(vasodilation [血管擴張])
■ Heat carried in blood lost by radiation
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Homeostasis (體內平衡)
● ***Maintenance/control (of fluctuations) of constant internal environment in body of
organism
● ***Internal environment: includes factors, e.g.: water content of body fluids, body
temperature, pH, blood glucose levels
● This internal environment must be kept carefully within certain narrow limits, to keep
organism healthy — if limits exceeded, organism may die
Control of body temperature in humans
● Change in body temperature → effect on enzymes and their response to changes
in temperature
● ***Core body temperature: that of blood circulating around body organs; kept close
to 37˚C
● When taking part in physical activity, active muscles respire more glucose providing
energy for muscle contraction; respiration releases heat as by-product →
blood carries away heat from internal organs to body surface (skin) → heat
lost to surroundings
● Temperature receptors and their role (involving sweat glands, skin
blood vessels, skin hairs)
○ Sweating
■ Sweat - watery fluid, containing some mineral salts (including NaCl)
and urea (trace amounts)
■ ***Sweat glands draw water out from blood capillaries under skin, then
sweat passes up sweat duct to skin surface
■ Liquid evaporates from skin surface, and to do this, heat
taken from skin → causes cooling
■ If humid, sweat does not evaporate easily, therefore feels
uncomfortable (as less cooling)
○ Skin blood vessels
■ Contribute to temperature control by changing blood volume which
flows near skin surface
■ When body temperature ↑, arterioles expand; allowing more
blood flow through blood capillaries near skin surface
(vasodilation [血管擴張])
■ Heat carried in blood lost by radiation
1
