Homeostasis Flashcards
Define “homeostasis”
Maintenance of internal stable environment in an organism within narrow limits even as external conditions fluctuate
What are the principles of homeostasis? 2
- Kept within dynamic equilibrium fluctuating at normal level
- Each condition controlled has norm/set point optimum for this condition
What is homeostasis vital for? 2
- Cell normal function to stop cellular damage
- Important in exercise for increased respiration, glucose use and body temperature
How is negative feedback carried out?
- Receptors used to detect deviations from the norm in response to a stimulus
- Connected to control centre
- Emits signals
- Turns effectors on/off to bring conditions back to the norm
Give the 2 types of signals emitted by control centres
- Nerve impulses
- Hormones
Give the 2 types of effector
- Muscles
- Glands
What are the two types of feedback?
- Negative feedback
- Positive feedback
Define negative feedback
Deviation from the norm results in a change in the opposite direction back to the norm
What is the limit of negative feedback?
- Only works in certain limits
- If the change is too big, effectors may not be able to counteract it
Describe negative feedback in glycolysis 7
- When level of ATP rises
- Inhibits enzyme catalysing early step in metabolic pathway
- ATP binds to enzyme
- Changes shape of enzyme and active site
- Enzyme substrate complex can’t form
- Enzyme activity inhibited
- Stops further glycolysis
Describe negative feedback in a species 2
- Environment supports a particular size population for a species as a norm
- If population increases competition or predation causes population size to fall back to norm
What is positive feedback? 2
- Output from control centre causes effectors to amplify a change
- Moves condition further from norm set point
When is positive feedback used? 2
- To rapidly activate something
- When homeostatic system breaks down e.g hypothermia
Is positive feedback a part of homeostasis and why/why not?
No - doesn’t keep internal environment stable
Explain blood clotting as an example of positive feedback 6
- Blood vessel damage
- Platelets become activated and release chemicals
- Attracts more platelets to be activated
- These release more chemicals
- Until a blood clot is formed
- Process ends with negative feedback as body detects blood clot
Why is a high temperature bad for the body? 5
- Enzyme molecules vibrate too much
- Breaks hydrogen bonds holding them in 3D shape
- Active site shape is changed and no longer works as catalyst
- Enzymes are denatured
- Metabolic reactions less efficient
Why is a low temperature bad for the body?
Reactions would occur too slowly for body to remain active
How does homeostasis control body temperature? 6
- Thermoreceptors detect changes in blood temperature [skin/in hypothalamus itself]
- Send impulses along sensory neurones to hypothalamus
- Sends impulses along motor neurones to effectors
- Respond to restore body temperature back to normal
- If too warm: initiates heat loss responses and inhbits heat gain responses
- If too cold: the opposite
Give 5 heat loss responses
- Hairs lie flat
- Vasodilation
- Sweat glands stimulated to secrete sweat
- Liver reduces metabolic rate
- Skeletal muscles relax: no shivering
- Evaporation from moist lung surfaces
How do hairs lie flat and how does this increase heat loss? 5
- Erector pili muscles relax
- Hairs lie flat
- Less heat is trapped
- Skin is insulated less
- Heat lost more easily
How does vasodilation occur and how does this cause heat loss? 5
- Shunt vessel constricts
- Muscles in arteriole walls relax
- Blood flows through them making them dilate
- More blood flows through capillaries in surface layer of dermis
- More heat energy lost through skin via radiation
How do sweat glands being stimulated to secret sweat allow for heat loss?
- Released on skin via sweat duct
- Evaporates, taking heat energy from skin
- Skin cools
Give 6 heat gain responses
- Sweat glands inhibited
- Vasocontriction
- Hairs stand up
- Liver increases metabolic rate
- Hormones released increasing metabolic rate
- Skeletal muscles contract: shivering
How does the inhibition of sweat glands ensure heat is gained?
Heat lost via evaporation reduced
How does vasoconstriction occur and why does this lead to heat gain? 5
- Muscles in arterioles constrict
- Reduces blood supply to surface capillaries
- Blood diverted through shunt vessels - they dilate as more blood flows through them
- Blood flows further from skin surface as less blood flows through capillaries in surface layers of dermis
- Reduces heat loss from skin via radiation
How do hairs stand up and why does this increase heat gain? 5
- Erector pili muscles contract
- Hairs stand up
- More air is trapped
- Skin is more insulated
- Heat lost less easily
What hormones produced increase metabolic rate?
- Adrenaline
- Thyoxine
Why does increasing metabolic rate increase heat gain?
More metabolic reactions leads to more heat energy
