1. Importance of Homeostasis 1). It can maintain the composition of the body in fairly strict limits. ( ion concentrations, pH, blood gasses, T℃ etc). 2). It results in normal functions. 2. How is the homeostasis achieved ? This is done by several regulation mechanisms， particularly the feedback control. 3. 3 patterns of regulation: Nervous Regulation （神经调节) Hormonal Regulation （体液调节） Autoregulation （自身调节） 4. Nervous Regulation Characteristics: ① It responses fast. ② It acts exactly. ③ Duration is short. 5. Hormonal Regulation Characteristics : ① It responses slowly. ② It acts extensively. ③ It lasts for long time. 6. Auto-regulation Characteristics: ① Amplitude of its effect is smaller than other two types. ② Extension of its effect is smaller than other two types. Role: only a supplement to the actionsof other two types of regulations. 7. Negative feedback Significance: Reverse effect of original stimulus. Prevent small changes from becoming too large. Help maintain homeostasis. This is the most common and important control mechanism in the body. 8. Positive feedback Significance: amplify changes or response and enhance or reinforce action of original stimulus so as to promote an activity to finish. sometime useful ,But sometime it is known as vicious cycle （恶性循环）because it can lead to instability or even death ! 9. Interaction between two types of feedback Normally the negative feedback can overcome the positive feedback, thus a vicious circle fails to develop. 10. Feed-Forward Control Significance It makes human body to foresee and adapt the environment promptly and exactly. an adaptive control 11 . Summary of Control of Body Function ① Homeostasis is kept by feedba...
