Homeostasis Flashcards
Define stimulus and response
Stimulus: change to external environment
Response: change in organism’s behaviour or physiology in response to a stimuli
Define homeostasis
Maintaining a constant internal environment despite external/internal changes
Define negative feedback
Reversal of a change to bring the system back to optimum
Define positive feedback
Increasing a change, taking the system further away from optimum
Outline the basic mechanism of negative feedback
Change away from optimum
Sensory receptor detects change (input)
Communication system informs effector (output)
Effector reacts to reverse change
Returns to optimum condition
Outline the mechanism of temperature control by negative feedback
Fall in core temp below 37 degrees
Thermoregulatory centre in hypothalamus detects change
Nervous & hormonal systems carry signals to skin, liver & muscles
More heat generated
Temp rises
Vice versa
Despite negative feedback a core body temp could be measures above or below the optimum. Why?
A slight overshoot during time taken for response to be initiated
Why does body temp need to stay within a narrow range of 37 degrees
So enzymes and other proteins can function and aren’t altered tertiary structure
Outline the basic mechanism of positive feedback
Change away from optimum condition
Receptor detects change (input)
Communication systems inform effectors (output)
Effectors react to increase change
Moves further away from optimum
Outline the mechanism of cervix dilation during pregnancy
Cervix begins to stretch
Posterior pituitary gland secretes more oxytocin hormone
Once fully dilated, baby is born & oxytocin production ends
Is neurone activity positive or negative feedback?
Positive - more membrane channels open to increase depolarisation
What is an ecotherm?
Organism that relies on external heat sources to maintain body temp
What is an endotherm?
Organism that uses heat from metabolic reactions to maintain body temp
Advantages of ectothermy
Less food used for respiration- more energy can be used for growth
Can survive for longer periods w/out food so dont need to find it often
Disadvantages of ectothermy
Less active in cooler temperatures - at risk of predatation and cant take advantage of available food when cold
What do ectotherms do when they are too cold?
Move to sunny area
Lay on warm surface
Expose a larger surface area to sun
What to ectotherms do when too hot
Reduce body surface exposed to sun
Move out of sun
Move underground
Advantages of endothermy
Remain active whatever the temperature- can always take advantage of prey or escape predators
Can inhabit colder parts of planet
Disadvantages of endothermy
Use lots if energy intake to maintain body temp (higher metabolic demand)
Need more food
Lower proportion of energy and nutrients used for growth
May overheat in hot weather
Physiological response to endotherms being too hot
Skin: sweat glands secrete swear- uses heat from blood as latent heat of vaporisation when it evaporates
- hairs / feathers lay flat to reduce insulation
- vasolidstion of precapillary sphincters directs blood to skin surface so more eat radiated away from body
Gaseous exchange system: increased breathing rate therefore evaporation of water from surface of lungs & airways; used heat from blood as latent heat of vaporisation = PANting
Liver: metabolism slows; less respiration; less heat released from exergonic reactions
Skeletal muscles: fewer contractions; less heat released
Blood vessels: dilation to direct blood to extremities
Physiological response to endotherms being too cold
Skin: less sweat secreted; less evaporation so less heat used, hairs/feathers erect to trap air (insulates), vasoconstriction of arterioles & precapillary sphincters leading to skin surface; blood diverted away from surface
Gaseous exchange system: slower breathing rate so less heat lost through evaporating water
Liver: increased metabolism therefore respiration therefore heat production
Skeletal muscles: spontaneous muscle contraction (shivering) releases heat by exergonic reactions of respiration
Blood vessels: constrict to limit blood flow to extremities; so blood isnt cooled as much
Behavioural responses to endotherms being too hot and too cold
Too hot: hide from sun, reduce surface area exposed to sun, remain inactive and spread limbs out to enable greater heat loss, wet skin to use evaporation to cool the body (eg cats licking self)
Too cold: lay in sun, orientate body towards sun to increase SA exposed, be more active to generate heat, remain dry
What do peripheral temperature receptors do?
Skin receptors that monitor temperature in extremities and send info to hypothalamus if it is very hot or very cold so that behavioural mechanisms are initiated - the person starts to FEEL hot/cold so will move to shade/heat source
What does homeostasis need to maintain?
blood pH, core temperature, blood conc. of urea & sodium ions
