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