Re: Do we have positive feedback in our body?

Yes, there are some processes that use positive feedback.   Blood clotting 
is one such example.  Bleeding causes a cascade of reactions to occur that 
"feed forward" to generate the next agent in the clotting process. 
Ultimately however the bleeding is stopped, thus the process terminates in 
a negative feedback step.  There are some other examples in the endocrine 
system of hormones acting in a positive feedback mechanisim to cause the 
release of another hormone.  In general, though, the majority of 
physiological processes use negative feedback.  If you need more specific 
examples of positive feedback please let me know.