Positive and Negative Feedback Mechanisms

What is homeostasis?

The tendency toward a relatively stable equilibrium between interdependent elements, especially as maintained by physiological processes

What is a negative feedback loop?

A biological process that counteracts a change to maintain a stable internal environment, a state known as homeostasis

Explain how the thermostat in your house uses a negative feedback system to maintain your home’s temperature.

By sensing when the temperature deviates fr9m a set point and taking the opposite action to correct it

Explain how your body maintains its temperature at roughly 98.6 degrees Fahrenheit under the following conditions:

a. You walk outside in January and the temperature is 30 degrees Fahrenheit

Hint: Peripheral vasoconstriction, shivering, increased metabolism, and behavioral responses

• Peripheral vasoconstriction: Blood vessels near the skin’s surface, which limits blood flow to the skin and extremities to minimize heat loss from the core to the cold environment

• Shivering: Muscles rapidly contract and relax to generate extra heat through increased metabolic activity

• Increased metabolism: The body may increase its metabolic rate to burn more calories and generate more internal heat

• Behavioral responses: The sensation of feeling cold prompts actions like putting on more clothes or moving to a warmer area

Explain how your body maintains its temperature at roughly 98.6 degrees Fahrenheit under the following conditions:

b. You walk outside in August and the temperature is 102 degrees Fahrenheit.

Hint: Vasodilation, sweating, decreased metabolism, and behavioral responses

• Vasodilation: Blood vessels near the skin’s surface widen, increasing blood flow to the skin to allow heat to radiate away from the body’s core to the cooler skin surface and then to the environment

• Sweating: Sweat glands produce perspiration on the skin. As the sweat evaporates, it carries heat away from the body, providing a significant cooling effect.

• Decreased metabolism: The body’s metabolic rate might slow down slightly to reduce the amount of internal heat being produced.

• Behavioral Responses: The sensation of feeling hot prompts actions like seeking shade, wearing lighter clothing, or taking a break from strenuous activity.

What is a positive feedback loop?

A process where a product of a reaction amplifies the original stimulus, creating a “snowballing” or “chain reaction” effect that drives a system further away from its starting point to completion

Explain how fruit ripening is an example of positive feedback. Hint: Initial signal, stimulation, amplification, and reinforcing the cycle.

• Initial signal: As a fruit begins to ripen, it starts to release ethylene gas.

• Stimulation: This ethylene gas acts as a signal to nearby unripe fruits, stimulating them to begin their own ripening process.

• Amplification: These newly ripening fruits then start to produce and release even more ethylene.

• Reinforcing cycle: This process continues in a cycle: more ripening fruits produce more ethylene, which causes more fruits to ripen, leading to the rapid and simultaneous ripening of multiple fruits on a plant.

What type of feedback help to maintain homeostasis?

• Negative feedback; reverses the initial stimulus; for example, if your body temperature rises, a negative feedback loop will trigger responses to lower it back down; if it gets too cold, it will trigger responses to warm it up