1 2 3 4 5 6 7 8

This requires three components:

1. Receptor- detects change in environment 2. Control center- processes information 3. Effector- responds to change

Humans use these mechanisms to regulate temperature (37ºC), blood glucose (800 mg/ml), O2 (100 mm Hg), CO2 ( 40mm Hg), Na+ (142 mEg/L) and K+ (4 mEq/L).

D. Negative vs Positive feedback

40.12

Negative feedback: a change in a variable triggers a response that counteractsthat change. For example, a thermostat senses that the temperature has fallen below the set point and activates the furnace to heat the room.

Positive feedback: a change in a variable triggers a response that augmentsthe change. For example, during childbirth, when contractions are detected by stretch receptors, they signal the hypothalamus to release a hormone (oxytocin) that stimulates more contractions. Rather than reestablishing equilibrium, positive feedback leads to a definite conclusion.

(Campbell, 4th,Ch. 36, especially pp mid 785-792. )