Do you think that in hash function can be decrypted and reversible?
No, they cannot be decrypted. These functions are not reversible. There is no deterministic algorithm that evaluates the original value for the specific hash.
However, if you use a cryptographically secure hash password hashing then you can may still find out what the original value was. These functions were designed to produce hash codes for big volumes of data / files. That is why they were designed to be very fast. It is relative easy to calculate MD5 and SHA1 hashes over a big number of inputs and use that to create a reverse lookup table.