8What is the ...Variable?Stimulus?Receptor?Control center?Effector?
9What is the ...Variable?Stimulus?Receptor?Control center?Effector?Receptors aren’t shown on this picture, but there are two sets of thermoreceptors: some in the hypothalamus to measure internal temperature , and some in the skin to measure external temperature
10You do: What is the ...Variable? Stimulus? Receptor? Control center? Effector?
11Receptors aren’t shown again, but there are two types of calcium receptors scattered throughout the bodyYou do: What is the ...Variable? Stimulus? Receptor? Control center? Effector?
12Negative Feedback Mechanisms Most homeostatic mechanisms are examples of negative feedback. In negative feedback, the output acts to change the direction of the stimulus. Example: If the body is hot, the hypothalamus will activate the sweat glands and dilate the blood vessels (the two outputs) … both of which will act to reduce the body temperature.
13Positive Feedback Mechanisms Some processes in the body are positive feedback mechanisms. In positive feedback, the output enhances the stimulus
14Positive or Negative Feedback? Blood ClottingBlood Pressure
15Positive or Negative Feedback? Blood ClottingBlood PressurePositive –The output (platelet adhering) increases the original stimulus (platelet-attracting chemical)Negative–The output (decreased heart rate / increased diameter) decreases the original stimulus (high blood pressure)
16Positive and Negative Feedback In pairs, write a Venn diagram comparing and contrasting positive and negative feedback. Also, identify other examples of positive and negative feedback and be prepared to justify why they are examples. ** may be in or out of the body** (5 minutes)
17Homeostatic Imbalance Most disease is caused by a disturbance of homeostatic mechanisms known as homeostatic imbalance.Homeostatic imbalance can result fromAgingGenetic mutationsPathogensEnvironmental factors