what is the immediate response of human body soon after a poisoning.what type of reactions take place?

Answer 1

One cannot generalize, except that it depends on the poison, and the dose.

Rattlesnake venom, lead, mustard gas, and poision ivy all evoke different reactions, and those reactions depend on the dose.

Answer 2

It depends upon the type of poison.

For some of the symptoms, see
http://www.emedicinehealth.com/poisoning/page3_em.htm