How do snakes produce their venom?

Recently I have come to know some interesting facts about snakes. As I always write about the things which make me surprise , even today I am writing the same. Snake venom is made by organs which are evolved from its salivary glands. Even we have salivary glands. What is the work of saliva? It contains enzymes which help to chew the food and thus helps in digestion. But saliva of snakes contain ever more toxic enzymes , that make it poisonous. The toxins in snake's venom contain complex mix of proteins that alter blood pressure, prevent blood clotting and paralyze nerves. That's why we die when a poisonous snake byte us if we don't receive medical help immediately.