Positive and Negative Feedback

Positive Feedback

• Designed to accelerate or enhance a response that has already started

• Pushes systems outside of their normal range

Positive Feedback Example

• Childbirth– Pressure receptors encourage the release of

Oxytocin in the Pituitary Gland– Oxytocin causes contractions – Pressure increases on the pressure sensors– After the child is born, the pressure receptors

are no longer stimulated and Oxytocin production ceases

Pressure Sensors cause the release of oxytocin

Oxytocin causes contractions to intensify

More intense contractions cause more pressure

Positive Feedback Example

• Blood Clotting– A tear in the capillary wall exposes collagen– Exposed collagen encourages platelets to adhere– Platelets release chemicals to encourage platelet

production and to encourage constriction of the wound

– This constriction exposes more collagen– More platelets to adhere and release chemicals

encouraging the production of more platelets

Collagen is exposed in the damaged capillary

Platelets bind to the collagen

Platelets release chemicals into the blood

Chemicals increase platelet production and constrict the

capillaries exposing more collagen

Negative Feedback

• Designed to maintain the body systems within appropriate parameters

• Keeps delicate systems working ideally and preserves body function

Negative Feedback Examples

• Calcium Levels– If calcium levels in the blood are too low the

parathyroid releases parathyroid hormone– Parathyroid hormone causes the bones to

release calcium– Parathyroid hormone also causes intestines

to absorb more calcium– Blood calcium levels then return to normal

Negative Feedback Example

• Calcium Levels cont’d– If your calcium levels in your blood are too

high– The thyroid produces calcitonin– Calcitonin increases the uptake of calcium to

the bones– Calcium levels return to normal

Facebook Activity

• Create a Facebook Profile for a gland on paper– Profile picture of what the gland looks like– Where the gland is located in the body– The hormones the gland secretes– The tissues or hormones it interacts with, or

interact with it and the effects– Conditions that may result from a malfunction

of the gland