What is the difference between organic and functional mental disorder?

What is the difference between organic and functional mental disorder?
"Organic disease" is caused by an identifiable condition with clinical examination and laboratory findings. There is a "lesion" that can highlight objectively.
Conversely, if you have for example epigastric pain, but no lesion is found, neither by endoscopy or by imaging, we say, after a comprehensive review, that your pain is functional.

Pretty bad i would assume.

So you and your partner don’t get sexually transmitted diseases and so your partner doesn’t get pregnant