3.6.4.1 - principles of homeostasis and negative feedback

homeostasis

maintenance of a constant internal environment within restricted limits

negative feedback

when stimulus causes corrective measure to be turned off to reduce the change, however could also lead to separate corrective measure being switched on to reduce the change

positive feedback

when the stimulus causes the physical change to remain on, to increase the change

negative feedback loop

input (change to system), receptor (change detected), coordinator (stores operational info, coordinates effectors), effector (brings change to system to return to optimum), output (system returned to optimum)

factors which need to be controlled in the body

temperature, water potential, ph, glucose/salts, co2, blood pressure

why does temperature need to be controlled in the body

at low temp enzymes have reduced ke so ror is lower as less likelihood of successful collisions, at exceedingly high temp enzymes become denatured due to bond breakage

why does ph need to be controlled in the body

small deviations from optimum ph reduces rate of enzyme controlled reactions due to h+/oh- clustering, large deviations cause enzymes to become denatured due to bond breakage

why does water potential need to be controlled in the body

affects osmosis into/out of cells leading to crenation or lysis

why do glucose/salts need to be controlled in the body

affects water potential, cells require constant supply of respiratory substrate

role of sweat glands in the skin in thermoregulation

when too hot - increased sweating from sweat glands so more evaporation of sweat from skin surface to remove heat from blood, when too cold - decreased sweating

role of hairs on skin in thermoregulation

when too hot - hair erector muscles relax, hairs lie flat on skin, no air trapped, when too cold - hair erector muscles contract, hair stands up, layer of warm air trapped around body

role of arterioles leading to capillaries in thermoregulation

when too hot - vasodilate so warm blood flows to capillaries and heat radiated out, when too cold - vasoconstrict so blood shunted through vessels closer to body core so less radiation of heat

role of liver cells in thermoregulation

when too hot - lower metabolic rate, when too cold - higher metabolic rate

role of skeletal muscles in thermoregulation

when too hot - no shivering, when too cold - involuntary contraction (shivering) requiring atp from respiration to release heat

behavioural changes in thermoregulation

when too hot - seeking shade, burrows, licking, when too cold - sheltering, basking in sun, huddling

ectotherms

body temp changes with external temp, cannot increase respiration rate

endotherms

maintain body temp within strict limits, independent of external temp