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Osmoregulation, micturation, and defecation reflex

Using the negative feedback system, explain how osmoreceptors and CO2 receptors maintain water balance and respiratory rates. Include a diagram.
How are micturation and defecation reflexes different?

NOTE: Moved from Physiology to Biology to expose question to different Online TAs.

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Solution Preview

This question is asking you to think about biological feedback systems. The first step to answering this question is to understand more about the types of feedback systems (or loops). Feedback systems are commonly categorized as negative or positive.


Feedback: A control system in which sensory information is sent to a controller; the controller then regulates a variable.

Negative feedback: Tends to keep things constant by reversing the direction of the change/reaction and thus allows for the maintenance of homeostasis (or internal equilibrium). For all variables there is a set point, which is the desired value, (for human temperature it would be 98.6 F). Feedback sensors detect the value of the variable and if it is not at the set-point it sends an "error message" to the controller that is proportional and opposite to the difference between the set point and the actual value (so if your temp was 100.6 the difference would be +2 degrees F, so the negative feedback would tell the control to change -2 degrees F). This feedback initiates a set of effectors that make appropriate changes (in this example a cooling of 2 degrees) to re-acheive the set-point. For example: You eat a candy bar. Sensors in your circulatory system detect an increase in blood sugar levels (say +40 mg/dl) and send a signal (we ...

Solution Summary

In this solution I define feedback loops (negative and positive), before explaining how osmoregulation, micturation, and the defecation reflex differ in their types of feedback.