1. Homeostasis

9. Feedback Control The word “feedback” means a process in which a part of output (feedback signal) from controlled organ returns to affect or modify the action of the control system. Feedback control mechanism consists of two forms: negative and positive feedback control.

10. The feedback signals from controlled system produces effect opposite to the action of the control system. The opposite effect is mainly “inhibitory action”. Negative feedback

11. Control Systems (Negative feedback in cardiovascular and endocrine systems) Reference Signal Comparator Controller Effectors Regulated Variable Sensor Feedback Signal Error Signal

12. Hyperthermia Heat receptors in the skin Hypothalamus Stress Sensors Control Center Increased activity of sweat glands Increased blood flow to the skin Effectors Perspiration evaporates cooling the skin Effect Stress is reduced shutting down mechanism Homeostatic Regulation of Body Temperature through Negative Feedback

13. Homeostasis Using a Neural Pathway Control center Many homeostatic mechanisms use a nerve pathway in which to produce their effects. These pathways involve an afferent path which brings sensory messages into the brain and an efferent path which carries outgoing nerve messages to effectors.

14. Hyperglycemia Pancreas-beta cells Sensor and Control center Insulin is released into blood Liver and Muscle cells take up glucose from the blood Effectors Blood glucose is reduced Stress is reduced shutting down mechanism Stress Homeostatic Regulation of Blood Sugar through Negative Feedback

15. Negative Feedback Via a Hormonal Pathway Regulation of Blood Sugar Hormones play an important role in many homeostatic pathways. Hormones are produced by endocrine glands. They enter the blood after being produced and travel throughout the body. However, hormones have their effect on specific target tissues.

18. Homeostatic Regulation of Child Birth through Positive Feedback Pressure of Fetus on the Uterine Wall Nerve endings in the uterine wall carry afferent messages to the Hypothalamus Production and Release of Oxytocin into the Blood Increasing strength of uterine contractions Intensifies The birth of the child will bring this process to a close. Other examples of positive feedback regulation occur during milk letdown and blood clotting.

19. Positive feedback “mini-loops” are built into pathway to speed up production of chemicals needed to form the clot. Entire sequence of clotting is a negative feedback pathway: Feedback in Coagulation

20. Importance: 1) Enhance the action of original stimulus or amplify or reinforce change, promote an activity to finish 2) It is known as a vicious circle because it can lead to instability or even death

21. Feed-forward control Concept: a direct effect of stimulus on the control system before the action of feedback signal occurs. Here the direct effect of the stimulus is termed disturb signal or interfere signal . Example: Shivering before diving into the cold water

22. Significance of Feedback-forward : adaptive feedback control. makes the human body to foresee and adapt the environment promptly and exactly (prepare the body for the change).