9.2 - Homeostasis and Feedback Mechanisms Flashcards
What is a feedback mechanism
A cycle/loop
What does a negative feedback loop do?
Restores normal conditions/brings body back within acceptable range by making adjustments
Example of negative feedback?
Household thermostat: when room temp falls below set point (20 degrees for ex.), the thermostat switches off the furnace
-> negative feedback b/c a change in the variable being monitored triggers control mechanism to COUNTERACT any further change in the same direction
Why is negative feedback loop “negative”? Give an example
Because the response of the system cancels or counteracts the effect of the original environmental change
Example: regulation of body temp:
cooling - evaporation of sweat and dilation of blood vessels
heating - constriction of blood vessels, shivering, and body hair sticking up
When does negative feedback occur?
When a system responds to change by attempting to compensate for this change
3 components of a negative feedback mechanism and explain
Sensor - detects changes in body conditions
Integrator - compares sensory info to desired set point (tells what to do) -> usually brain
Effector - acts to re-establish homeostasis (a muscle or gland)
Define stimulus
Environmental change
Define response
Systems output
List 5 stages of negative feedback in order
stimulus -> sensor -> integrator -> effector -> response
What are the special sensors in the organs of the body? What do they do?
Monitors - signal a coordinating center once an organ begins to operate outside its normal limits
-> sends info to regulator to restore normal balance
Why do arterioles dilate?
They have a large diameter to allow blood to radiate thermal energy/heat
- > allow for more blood flow to skin!!
- > as sweat evaporates, it releases heat as well to cool body off
State sensor, integrator, and effector for when: you feel cold, so blood vessels in skin constrict to minimize loss of thermal energy
Sensor: nerve cells (thermoreceptors)
Integrator: brain (hypothalamus)
Effector: skeletal muscles (contain blood vessels)
State sensor, integrator, and effector for when: a driver sees the car is moving over the speed limit, so takes her foot off the accelerator
Bonus: what is the negative feedback of this?
Sensor: eyes
Integrator: brain
Effector: foot muscles (contract)
- negative feedback prevents further slowing down*
State sensor, integrator, and effector for when: you get a cut in your leg and begin to bleed
Sensor: skin (pain)
Integrator: brain
Effector: arm/hand (putting pressure to initiate blood clotting) behavioural response
Label negative feedback loop with terms: sweat gland, thermoreceptors in skin, sweat, thermoreceptors in hypothalamus (brain), skin blood arterioles, increase in thermal energy
Stimulus: increase in thermal energy (heat)
Sensor: thermoreceptors in skin (detect increase in body temp.)
Integrator: thermoreceptors in hypothalamus (brain)
Effector: sweat gland
Response: sweat (flushed red), and skin blood arterioles (can expand/constrict)
-> arterioles dilate to release blood, which releases heat
What is the negative feedback of sweating a lot? How?
Sensor detects body temp between points
- brain is informed, so effectors stop what they are doing (no more sweat/dilation)
Which types of organisms use feedback loops to regulate INTERNAL processes?
Mammals - can stay at set point even in extreme temperatures/conditions
List 4 examples of negative feedback mechanisms in animals. Are they physiological or behavioural?
1) birds and dogs pant to release thermal E from body -> physiological
2) reptiles bask on sunny rocks to absorb thermal E & move to cooler areas -> behavioural
3) insects bask in sunlight to warm their muscles/contract their flight muscles (like shivering) - dragon flies, bees, moths -> behavioural
4) fish (tuna & hunting sharks) contract swimming muscles to generate thermal E -> physiological
What is positive feedback?
- allows a discrete physiological event to be accomplished RAPIDLY *
- less common in the body
- reinforce change
- move controlled variable further away from steady state
Why is positive feedback “positive”? Purpose?
It INCREASES the change in environmental condition instead of reversing the change, causing the system to become UNSTABLE
- > away from norm in extreme way
- > has to be drastic and fast
- > purpose is to accomplish a specific goal quickly
Give examples of positive feedback loop in humans
1) child labour - uterine contractions cause hormone oxytocin to be released, resulting in intensified contractions -> more oxytocin -> stronger contractions
- > increases pressure (positive feedback) allows quick delivery of baby
2) breastfeeding - sensation of suckling -> production of milk (FAST) -> more suckling = more positive feedback
3) animal running from predator - adrenaline spikes, blood sugar and hormones increase
In what way is the examples of positive feedback not homeostasis?
More suckling of milk and labour increase production of a certain variable, SYSTEM moves further away from set point/ dynamic equilibrium
-> instead of inhibiting future milk production, it make the system unstable (* creating extreme conditions *)
Why is it good for the body not to be in homeostatic balance at certain times?
Because the body may need a continuous increase in some INTERNAL VARIABLE, such as when an animal is attacked/frightened (flight or fight response!!)
* to accomplish a specific goal quickly *
How does child labour work in terms of feedback mechanisms?
- Pushing on the cervix is the stimulus (pressure) -> transmitted to brain
- Receptor is the nerves in cervix
- hormone oxytocin travels through blood to UTERUS
- pituitary gland releases oxytocin
- hormone tells uterus to contract, and response is contractions of uterus, and baby’s head pushing continues the pressure process (reinforcing change), and stronger muscle contractions
Explain what happens when you exercise with negative feedback flowchart
-> raises CO2 levels in the blood
Sensor: monitors CO2 & detects any inc. or dec. out of the range
(Chemoreceptors (cells) located in arteries)
Integrator: sensor sends message to brain of high CO2
Effector(s): carry out the response after receiving messages from integrator
- diaphragm and rib (intercostal) muscles -> contract faster to SPEED UP breathing
Response: breath faster (to expel CO2)
What does negative feedback do after CO2 levels decrease with fast breathing after exercise?
Decrease of CO2 is detected, message sent to brain, quick breathing stops (goes to normal)
-> negative feedback prevents further decrease of CO2 levels
