Feedback Loops

What is homeostasis?

Ability of an organism to maintain a stable internal environment

Why is homeostasis a dynamic state?

Outside factors tend to change the internal environment and internal control mechanisms oppose these changes

What maintains homeostasis?

Feedback loops

What do feedback loops consist of?

Receptor/sensor, control center, effector, and response

What are receptors/sensors in feedback loops?

Structures that monitor a controlled condition and detect changes

What does the control center do in feedback loops?

Determine next action

What is the effector typically in feedback loops?

Muscle or gland

What does the effector receive?

Directions from the control center

What does the effector produce?

Response that restores the controlled condition

What is the response in feedback loops?

Change causing increase or decrease of the effect of the stimulus

What do negative feedback loops do?

Reverse the original stimulus and reduce the effect of the stimulus

What are most feedback systems in the body?

Negative feedback loops

What are negative feedback loops used for?

Conditions that need frequent adjustment

What do positive feedback loops do?

Intensify/amplify the original stimulus and increase the effect of the stimulus

What are positive feedback loops not used for?

Homeostasis

What are positive feedback loops used for?

Driving a vital process further away from its initial set point and to completion

What is thermoregulation?

Maintenance of a stable internal body temperature

What happens to skin blood vessels when body temperature is too high?

Dilation that allows warm blood to be carried near the skin’s surface

What happens to sweat glands when body temperature is too high?

Activation that causes secretion of perspiration for evaporative cooling

What eventually happens after body temperature gets too high?

Body temperature decreases

What happens to skin vessels after body temperature gets too low?

Constriction that forces blood away from the skin’s surface 

What happens to skeletal muscles after body temperature gets too low?

Activation that stimulates shivering in order to produce heat

What eventually happens after body temperature gets too low?

Body temperature increases

What is transpiration?

Movement of water in a plant from the root to the leaves

What does transpiration lead to?

Evaporation of water from the leaves

How does water evaporate?

Through tiny opening on the underside of leaves called stomata 

What closes stomata?

Guard cells

When do guard cells close stomata?

In times where transpiration is occurring too fast and water is being lost too quickly

What plant hormone do plants secrete when water availability is scarce?

Abscisic acid

What does abscisic acid trigger?

Shrinking of guard cells which causes stomata to close

What are thermoregulation and transpiration examples of?

Negative feedback loops

What are childbirth and the ripening of fruit examples of?

Positive feedback loops

What does the baby pushing on the cervix cause?

Pituitary gland to secrete the hormone oxytocin

What does oxytocin stimulate?

Contraction of the uterine wall

What does the contraction of the uterine wall push?

Baby against the cervix

When does the cycle of the secretion of oxytocin by the pituitary gland, contraction of the uterine wall, and pushing of the baby against the uterine wall end?

Upon delivery of the baby 

What plant hormone does ripening fruit release into the air?

Ethylene gas

What does ethylene gas accelerate?

Ripening of nearby unripened fruit

What happens upon the ripening of unripened fruit?

Release of more ethylene gas into the air

What does the positive feedback loops concerning fruit ripening cause?

All fruit to ripen together