Q:

PPV vs Sensitivity

I am looking at the equation PPV and Sensitivity
and I got this 
PPV = TP / (TF+FN)

and 
Sensitivity = TP / (TF+FN)

Which means both are the same !!
So do we have them in 2 names?
and how come F1 Score is 
F1 Score = 2*PPV*S / (PPV+S)

Can we rewrite F1 Score to be
F1 Score = 2*PPV*PPV / (PPV+PPV) = 2*PPV*PPV / (2*PPV) = PPV !!

They all the same?
It seems there is some condition or something I am missing here!
can someone please explain to me what am I missing? 

A:

Using medical diagnosis as an example:
sensitivity is the proportion testing positive among all those who actually have the disease.
Sensitivity = TP/(TP+FN) = TPR
While,
PPV is how likely a patient has a predicted specific disease given the test results. 
PPV = TP/(TP+FP) which is definitely NOT equal to TP/(TP+FN)!
Regarding F1:
F1 is the harmonic mean of precision and sensitivity. One is normalized by column and the other normalized by row. Precision is synonymous with PPV while sensitivity is synonymous with TPR.
F1 = 2*PPV*TPR / (PPV+TPR) 

