Feedback mechanism | Negative feedback | Positive feedback examples (Biology class 12)

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Feedback mechanism
Feedback is defined as the information gained about a reaction to a product, which will allow the modification of the product. Feedback loops are therefore the process whereby a change to the system results in an alarm which will trigger a certain result. This result will either increase the change to the system or reduce it to bring the system back to normal.

Negative Feedback

A negative feedback loop occurs in biology when the product of a reaction leads to a decrease in that reaction. In this way, a negative feedback loop brings a system closer to a target of stability or homeostasis. Negative feedback loops are responsible for the stabilization of a system, and ensure the maintenance of a steady, stable state. The response of the regulating mechanism is opposite to the output of the event.

Example: Temperature Regulation
Temperature regulation in humans occurs constantly. Normal human body temperature is approximately 37°C. When body temperature rises above this, two mechanisms kick in the body begins to sweat, and vasodilation occurs to allow more of the blood surface area to be exposed to the cooler external environment. As the sweat cools, it causes evaporative cooling, while the blood vessels cause convective cooling. Normal temperature is regained. Should these cooling mechanisms continue, the body will become cold. The mechanisms which then kick in are the formation of goose bumps, and vasoconstriction. Goosebumps in other mammals raise the hair or fur, allowing more heat to be retained. In humans, they tighten the surrounding skin, reducing (slightly) the surface area from which to lose heat. Vasoconstriction ensures that only a small surface area of the veins is exposed to the cooler outside temperature, retaining heat. Normal temperature is regained.

Positive Feedback Loops
A positive feedback loop occurs in nature when the product of a reaction leads to an increase in that reaction. If we look at a system in homeostasis, a positive feedback loop moves a system further away from the target of equilibrium. It does this by amplifying the effects of a product or event and occurs when something needs to happen quickly.

Example: Childbirth (Labour pain)

When labor begins, the baby’s head is pushed downwards and results in increased pressure on the cervix. This stimulates receptor cells to send a chemical signal to the brain, allowing the release of oxytocin. This oxytocin diffuses to the cervix via the blood, where it stimulated further contractions. These contractions stimulate further oxytocin release until the baby is born.