Negative Feedback

Key Questions

  • Negative feedback is activated by the body when something such as body temperature, pH of the blood, sugar concentration in the blood, gas concentrations, and water balance are not within very strict boundaries. It is a part of homeostasis.

    The diagram below shows how negative feedback helps keep the blood temperature between 35.8 and 37.8 degrees celcius , which are the limits the human body can take.

    As can be seen, a stimulus is needed to cause a drop or incease in blood temperature. A temparature that is too high will activate the heat-loss center in the hypothalamus, which causes blood vessels to dilate (so that heat can travel in the blood stream), and activates sweating (because the evaporation of sweat causes body temperature to decrease).

    In case the temperature is too low, skin blood vessels will contract (to keep the blood from losing heat), and shivering begins (the contraction of the muscle that occurs when one shivers causes heat).

    Image taken from bio119homeostasis

  • Negative Feedback during enzyme catalysed reaction occurs when there is excess formation of products.
    Continued accumulation of products may be harmful to the tissues , in order to prevent that the end products send negative feedback to prevent further formation of products.

  • Negative feedback shuts a process off.
    If you set you stove top temperature gauge to a set point, it will turn off the stove top. And it will turn the heat back on when the top cools. It keeps the process in balance.
    Most of our processes are regulated by negative feedback.

    Only a few are positive feedback. The one you may be most familiar with is blood clotting. Once damage occurs, blood flow to the site carries more and more platelets and fibrinogen until a clot forms that will keep the injury from losing any more blood. Otherwise, you could bleed out. This an over reaction, but one that can save your life.
    Two more examples of positive feedback are childbirth and breastfeeding.