The main difference between positive and negative feedback loops is that the positive feedback loops amplify the initiating stimulus, moving the system away from its equilibrium whereas the negative feedback loops counteract the changes of the system, maintaining them in a set point. Furthermore, positive feedback loops result in more products while negative feedback loops result in fewer products.
Positive and negative feedback loops are the two mechanisms that affect homeostasis, which refers to the tendency to maintain a relatively stable environment in biological systems.
Key Areas Covered
1. What are Positive Feedback Loops
– Definition, Characteristics, Examples
2. What are Negative Feedback Loops
– Definition, Characteristics, Examples
3. What are the Similarities Between Positive and Negative Feedback Loops
– Outline of Common Features
4. What is the Difference Between Positive and Negative Feedback Loops
– Comparison of Key Differences
Key Terms
Childbirth, Fruit Ripening, Homeostasis, Negative Feedback Loops, Positive Feedback Loops, Thermoregulation
What are Positive Feedback Loops
Positive feedback loops reinforce a particular change that occurs in the body. When a change is detected by a receptor, this type of feedback mechanisms promotes the change to proceed further. The amplification of the initial change occurs until the removal of the stimulus. Childbirth is one of the most precise examples of positive feedback loops. During childbirth, the pressure on the cervix due to the pushing of the child’s head downwards induces the release of oxytocin, which in turn stimulates further contractions of the cervix. Subsequently, these contractions stimulate the release of oxytocin further until the baby is born.
Figure 1: Childbirth through Positive Feedback Loops
Some other examples of positive feedback loops are as follows:
- Lactation – Breastfeeding stimulates milk production, which causes further feeding. This continues until baby stops feeding.
- Ovulation – The dominant follicle inside the ovary releases estrogen, which stimulates the release of FSH and LH. These hormones stimulate further growth of the follicle.
- Blood clotting – The release of clotting factors by the activated platelets stimulates the aggregation of more platelets at the site of injury.
- Fruit ripening – The ripened fruits release ethylene, which stimulates the ripening of the nearby fruits.
What are Negative Feedback Loops
Negative feedback loops are responsible for reversing the change by activating the opposite responses. This means this type of feedback mechanisms stabilize biological systems maintained under homeostatic conditions, important for a constant internal environment. Some examples of negative feedback loops are described below.
Thermoregulation
The regular body temperature of humans is 37 °C. When the body temperature increases, the mechanisms such as sweating and vasodilation, which release internal heat to the external environment, are induced. The evaporation of sweat from body surfaces uses heat in the body. Also, increased blood circulation near the skin through vasodilation carries internal heat to the surface of the body. Both of these mechanisms together cool down the increased body temperature. On the other hand, when the temperature of the body decreases, goosebumps and vasoconstriction help in increasing the body temperature by retaining the heat inside the body.
Figure 2: Thermoregulation
Blood Pressure Regulation
Baroreceptors detect blood pressure inside arteries and help to control the heart rate by sending signals to the brain.
Maintenance of the oxygen/carbon dioxide balance, blood sugar levels, blood pressure, acid/base balance, water balance (osmoregulation), calcium levels, blood pH, and energy balance are some other examples of negative feedback loops of the body.
Similarities Between Positive and Negative Feedback Loops
- Positive and negative feedback loops work on a stimulus, either increasing or decreasing its effect.
- Both play a critical role in homeostasis in biological systems.
Difference Between Positive and Negative Feedback Loops
Definition
Positive feedback loops refer to a feedback mechanism resulting in the amplification or growth of the output signal while negative feedback loops refer to a feedback mechanism resulting in the inhibition or the slowing down of a process.
Effect on Homeostasis
Furthermore, the positive feedback loops breakdown the homeostasis of the system while the negative feedback loops always maintain the conditions of homeostasis.
Occurrence
Also, the positive feedback loops are less common but, occur in specific situations while the negative feedback loops occur more often in the body, helping in maintaining various conditions of the body.
Examples
Some examples of positive feedback loops are childbirth, blood clotting, and fruit ripening while some of the examples of negative feedback loops are the regulation of body temperature, blood pressure, and fluid content.
Conclusion
Positive feedback loops are bodily mechanisms that increase the effect of a particular stimulus, as occurred during childbirth, lactation or fruit ripening. However, negative feedback loops counteract the changes of the system, maintaining them in a set point. The main difference between positive and negative feedback loops is the response of each feedback loop to the change.
Reference:
1. Cornell, Brent. “Feedback Loops.” BioNinja, Available Here
Image Courtesy:
1. “106 Pregnancy-Positive Feedback” By OpenStax – https://cnx.org/contents/[email protected]:fEI3C8Ot@10/Preface (CC BY 4.0) via Commons Wikimedia
2. “105 Negative Feedback Loops” By OpenStax – (CC BY 4.0) via Commons Wikimedia
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