Final answer:
In positive feedback, a stimulus is amplified, leading to an intensified and continuing response in the same direction until an endpoint is reached, such as in blood clotting and childbirth contractions.
Step-by-step explanation:
In positive feedback, an initial stimulus produces a response that amplifies the stimulus. This involves a reaction to some stimulus in the same direction as the stimulus, thus intensifying the effect rather than reversing it, leading to an unstable, runaway process. An example of a positive feedback loop is the cascade of chemical reactions that result in blood clotting. As one clotting factor is activated, it activates the next factor in the sequence until a fibrin clot is achieved. The process maintains the direction of the stimulus, potentially accelerating it, and is considered positive because it does not shift direction until a certain endpoint is reached.
Another common example of positive feedback is oxytocin-stimulated uterine contractions during childbirth. The presence of oxytocin leads to contractions, which cause more oxytocin to be released, further intensifying the contractions until childbirth occurs. This is a control mechanism that serves to intensify a response until an endpoint is reached, which is a characteristic of the positive feedback process in physiology.