Wiktionary
n. (context biology English) Any function of the body that is essential for maintaining life, especially breathing and circulation.
Usage examples of "vital function".
Now he was performing a vital function, an act upon which the future of House Harkonnen depended.
The first was that he was needed at Fortress Draconis, and that Fortress Draconis performed a vital function in keeping Chytrine bottled up in the north.
Our duties here are varied, but more or less our most vital function is to keep Tokyo as free as possible of terrorist incursion.
Surely, when no vital function of the Library is involved, they will be pleased to honor the Emperor and oblige his wishes.
It had always been obvious the the pol-com performed a vital function for somebody--presumably for the Estes Park Government.