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Homeostasis and feedback loops
Learning objectives
After completing this study unit, you will be able to:
- Discuss how homeostasis regulates body functions.
- Compare and contrast negative and positive feedback loops.
- Apply the concept of feedback loops to physiological mechanisms.
Introduction
Homeostasis ensures that the internal body environment remains stable even when the external environment changes. Homeostatic processes ensure that key characteristics of the extracellular fluid like temperature, composition, volume and pressure remain within ranges that are ideal for cellular function and survival. Failure of homeostasis often leads to pathology.
The main mechanism used to maintain homeostasis is negative feedback loops. Negative feedback loops have three main components:
- Sensor: detects the quantity of a variable
- Control center: determines how much the variable deviates from its optimal range
- Effector: changes the quantity of the variable
Variables under homeostatic control via negative feedback loops are called regulated variables, and the range a variable is maintained within is called normal range. When a regulated variable deviates beyond its normal range, the negative feedback loop brings it back to its optimal range. Examples of negative feedback loops include the regulation of blood pressure, sodium concentration, pH and volume of blood.
Positive feedback loops instead escalate a change in a variable, starting an ever-increasing cycle until a defined endpoint is reached. Positive feedback loops help promote quick responses when necessary, and include fetal progression during labor, blood clotting and transmission of action potentials in neurons.
Explore concepts
Homeostasis
Homeostasis helps maintain a stable internal environment despite changes in the external environment.
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Negative feedback loops
Negative feedback loops oppose changes to a variable, ensuring that regulated variables stay within their normal range.
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Positive feedback loops
Positive feedback loops escalate changes to a variable, ensuring that a defined endpoint is reached quickly.
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Summary
| Homeostasis | Maintenance of a stable internal environment of the body (the extracellular fluid), even when the external environment changes |
| Feedback loops: types |
Negative feedback loops: oppose changes in a variable to keep it within an ideal range of values Positive feedback loops: reinforce changes in a variable to escalate responses and reach an endpoint quickly |
| Feedback loops: examples |
Negative feedback loops: regulate body temperature, blood pressure, ion concentrations, blood volume Positive feedback loops: fetal progression during labor, blood clotting, action potential transmission |
| Negative feedback loops: definitions |
Regulated variable: sensed variables kept within a normal range Normal range: the ideal range of values of a regulated variable Non-regulated variable: variables altered by a negative feedback loop but not directly sensed |
| Negative feedback loops: components |
Sensor: monitors the quantity of a regulated variable and transmits information to the control center Control center: calculates how much a variable deviates from its normal range and sends to the effectors a signal proportional to the error detected Effector: increases or decreases the regulated variable, either directly or through non-regulated variables (e.g.: change heart rate to regulate blood pressure) |
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