Homeostasis August 15, 2016 Don’t forget organ system stuff before!

Homeostasis The maintenance of relatively stable internal conditions Dynamic process – the body is constantly regulating to keep conditions within acceptable ranges

Examples of Homeostasis Many variables are maintained by homeostasis. What examples can you think of?

Examples of Homeostasis Many variables are maintained by homeostasis. Examples include: Temperature Blood pH Blood sugar Water balance Blood pressure Ion balance

Homeostatic Control Mechanisms

Homeostatic Control Mechanisms Analogies Thermostat Cruise control others?

What is the ... Variable? Stimulus? Receptor? Control center? Effector? (some may not be listed on chart)

What 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

You do: What is the ... Variable? Stimulus? Receptor? Control center? Effector?

Receptors aren’t shown again, but there are two types of calcium receptors scattered throughout the body You do: What is the ... Variable? Stimulus? Receptor? Control center? Effector?

Negative 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.

Positive Feedback Mechanisms Some processes in the body are positive feedback mechanisms. In positive feedback, the output enhances the stimulus ** This is hard for students. Output must cause further change in the initial stimulus.

Positive or Negative Feedback? Blood Clotting Blood Pressure

Positive or Negative Feedback? Blood Clotting Blood Pressure Positive – 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)

Positive and Negative Feedback Come up with examples and non-examples of negative and positive feedback. (For non-examples, I want something that at first glance might seem like positive or negative feedback, but isn’t). What is it that distinguishes the true examples from the non-examples? Non-examples: + fever (that is actually negative feedback but with a higher setpoint than normal!), growth, running & heart rate - diffusion, bright sun pupil contract

Homeostatic Imbalance Most disease is caused by a disturbance of homeostatic mechanisms known as homeostatic imbalance. Homeostatic imbalance can result from Aging Genetic mutations Pathogens Environmental factors

Chapter 1 Summary due next class, Aug 17 First quiz Aug 19! Homework Chapter 1 Summary due next class, Aug 17 First quiz Aug 19!

Closure What are your key takeaways from our objectives? What was our LP and how did we use it? How does what we did today relate to our significant concept? Do Congo Line Review if time permits!

Exit Ticket Study this diagram. What is the stimulus? What are the effectors? Is this + or – feedback, and how can you tell?

Exit Ticket Identify the body system to which each organ belongs Pancreas Liver Ex) Which system cleans and returns body fluids to the blood stream?