9.2 - Homeostasis and Feedback Mechanisms

Question 1

What is a feedback mechanism

Answer 1

A cycle/loop

Question 2

What does a negative feedback loop do?

Answer 2

Restores normal conditions/brings body back within acceptable range by making adjustments

Question 3

Example of negative feedback?

Answer 3

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

Question 4

Why is negative feedback loop “negative”? Give an example

Answer 4

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

Question 5

When does negative feedback occur?

Answer 5

When a system responds to change by attempting to compensate for this change

Question 6

3 components of a negative feedback mechanism and explain

Answer 6

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)

Question 7

Define stimulus

Answer 7

Environmental change

Question 8

Define response

Answer 8

Systems output

Question 9

List 5 stages of negative feedback in order

Answer 9

stimulus -> sensor -> integrator -> effector -> response

Question 10

What are the special sensors in the organs of the body? What do they do?

Answer 10

Monitors - signal a coordinating center once an organ begins to operate outside its normal limits
-> sends info to regulator to restore normal balance

Question 11

Why do arterioles dilate?

Answer 11

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

Question 12

State sensor, integrator, and effector for when: you feel cold, so blood vessels in skin constrict to minimize loss of thermal energy

Answer 12

Sensor: nerve cells (thermoreceptors)
Integrator: brain (hypothalamus)
Effector: skeletal muscles (contain blood vessels)

Question 13

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?

Answer 13

Sensor: eyes
Integrator: brain
Effector: foot muscles (contract)

• negative feedback prevents further slowing down*

Question 14

State sensor, integrator, and effector for when: you get a cut in your leg and begin to bleed

Answer 14

Sensor: skin (pain)
Integrator: brain
Effector: arm/hand (putting pressure to initiate blood clotting) behavioural response

Question 15

Label negative feedback loop with terms: sweat gland, thermoreceptors in skin, sweat, thermoreceptors in hypothalamus (brain), skin blood arterioles, increase in thermal energy

Answer 15

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

Question 16

What is the negative feedback of sweating a lot? How?

Answer 16

Sensor detects body temp between points

- brain is informed, so effectors stop what they are doing (no more sweat/dilation)

Question 17

Which types of organisms use feedback loops to regulate INTERNAL processes?

Answer 17

Mammals - can stay at set point even in extreme temperatures/conditions

Question 18

List 4 examples of negative feedback mechanisms in animals. Are they physiological or behavioural?

Answer 18

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

Question 19

What is positive feedback?

Answer 19

• allows a discrete physiological event to be accomplished RAPIDLY *
• less common in the body
• reinforce change
• move controlled variable further away from steady state

Question 20

Why is positive feedback “positive”? Purpose?

Answer 20

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

Question 21

Give examples of positive feedback loop in humans

Answer 21

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

Question 22

In what way is the examples of positive feedback not homeostasis?

Answer 22

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 *)

Question 23

Why is it good for the body not to be in homeostatic balance at certain times?

Answer 23

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 *

Question 24

How does child labour work in terms of feedback mechanisms?

Answer 24

• 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

Question 25

Explain what happens when you exercise with negative feedback flowchart

Answer 25

-> 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)

Question 26

What does negative feedback do after CO2 levels decrease with fast breathing after exercise?

Answer 26

Decrease of CO2 is detected, message sent to brain, quick breathing stops (goes to normal)
-> negative feedback prevents further decrease of CO2 levels