homeostasis

word document with aids that help learning homeostasis.

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  • Created on: 13-01-09 19:19
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Biology Revision:
Homeostasis:
Homeostasis ­ maintaining internal conditions within narrow limits
Usually involves ­ negative feedback,
Effectors ­ are either muscles or glands, they bring about response
to a stimulus
Receptors ­ detect stimuli e.g. thermo receptors
Negative Feedback ­ departure from a set level is detected by
receptors. These send information to effectors which bring about a
return to the original value.
Thermo regulation - the regulation of body temperature
Endothermic animals ­ warm blooded e.g. mammals, birds. These
produce lots of heat and retain what is required
Exothermic animals ­ cold blooded e.g. reptiles, fish, and
amphibians. These produce less heat and retain very little of it.
Short-term heat production ­ (1) shivering ­ rapid contraction and
relaxation of muscle fibres. Major disadvantage ­ uses lots of
energy (2) release of hormone adrenaline ­ from adrenal glands,
this raises the metabolic rate of the individual.
Basal Metabolic Rate ­ energy expended by a resting fasting person
in a room at a comfortable temperate.
Factors that effect metabolic rate:
Age
Sex
Diet
Activity
Health
Drugs
Long-term heat production ­ increased production of the hormone
thyroxine from the thyroid gland in the neck.
Heat loss:
Radiation ­ loss of heat via electromagnetic waves
when body is warmer than the surroundings.
Evaporation ­ mainly via sweating
Conduction ­ the loss of heat through contact with an
object/medium that is cooler than the body
Regulation of heat loss:
Vasoconstriction and vasodilatation ­ alter blood flow
to the skin and hence regulate heat loss by changing
the diameter of the arterioles in the skin
Vasodilatation ­ widening of arterioles, increase blood
flow
Vasoconstriction ­ narrowing of arterioles decrease
blood flow
Erector pili muscle ­ reduce heat loss the muscles contract causing
hair to stand upright. This traps a still layer of air close to the skin
and reduces heat loss.
Adipose tissue ­ fat storage tissue

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Hot and cold thermo-receptors in the skin send nerve impulses to
the hypothalamus which brings about the changes necessary to
restore the correct temperature.…read more

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