homeostasis Flashcards
homeostasis definition
maintenance of a stable internal environment
negative feedback in homeostasis (increased temp)
receptors detect increase in body temp
hypothalamus/ thermoregulatory centre stimulated
send impulse to sweat glands
more impulses sent along sympathetic nerves
increased blood flow to surface of skin by vasodilation
so more warm blood flows near skin surface
negative feedback glucose conc
receptors detect blood glucose concentration increase
effectors act to shift the blood glucose concentration back
heat loss centre
stimulates sweat glands to secrete sweat
inhibits contraction of arterioles in skin
- hair erector muscles
- liver (to reduce metabolic rate)
- skeletal muscle contractions (they relax so there is no shivering
heat gain centre
stimulates: arterioles in the skin to constrict
- hair erector muscles to contract
- liver to raise metabolic rate
- skeletal muscles to contract in shivering
inhibits: sweat glands
sweat heat loss mechanism
released on skin via sweat duct
evaporates- taking heat energy from the skin
sweat glands stimulated by nerves from hypothalamus
hairs
raised in cold by contractions of erector muscles
traps a layer of air that insulates the body
vasodilation
controlled by hypothalamus
in warm conditions
shunt vessel constricts and muscles in walls of arterioles relax
blood flows through the arterioles, making them dilate
more blood flows closer to the surface so more energy is lost
vasoconstriction
in colder conditions
arteriole walls contract causing the arterioles to constrict
reduces blood supply to the surfce capillaries
blood diverted through the shunt vessel, which dilates as more blood flows through it
blood flows further from the kin surface so less energy is lost
changes to energy in body
evaporation from moist surfaces of lungs increases energy loss (breathing)
sweat evaporation increases energy loss
arteriole vasodilation increases blood flow to skin- increasing energy loss by conduction, convection and radiation
voluntary muscle contraction and involuntary shivering releases energy- raising body temp
arteriole vasoconstriction decreases blood flow to skin reducing energy loss
hairs raised by contraction of erector muscles reduces energy lossr
radiation
bodies usually warmer than the environment so we radiate energy
conduction
involves direct contact between objects and energy transfer from one ot another
convection
energy loss by bulk movement of air
evaporation
energy needed to convert water to vapour
energy required to evaporate sweat is drawn from the body- only has cooling effect when water evaporates
