Mid pair, top kicker - can I fold this?

[Analyst]

with apologies to spydog

MP has shown himself to be somewhat too loose (a fondness for limping early with Axo and small suited connectors) but not unreasonable postflop.

PokerStars 5/10 Hold'em (5 handed) converter

Preflop: Hero is BB with A[img]/images/graemlins/club.gif[/img], 7[img]/images/graemlins/spade.gif[/img].
<font color="#666666">1 fold</font>, <font color="#CC3333">MP raises</font>, <font color="#666666">2 folds</font>, Hero calls.

Flop: (4.40 SB) 6[img]/images/graemlins/spade.gif[/img], J[img]/images/graemlins/spade.gif[/img], 7[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets</font>, <font color="#CC3333">MP raises</font>, Hero calls.

Turn: (4.20 BB) 8[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">MP bets</font>, Hero calls.

River: (6.20 BB) 7[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">MP bets</font>, <font color="#CC3333">Hero raises</font>, MP calls.

Final Pot: 10.20 BB

I've been defending w/Ax pretty consistantly against all but UTG raisers, but am unsure if this is SOP.

The flop bet seems automatic. His raise could mean a J, 89, 45, etc., or even just overcards - a pretty wide range of hands.

On the turn, I'm not getting odds if behind but factoring the percent of times (and river bets as well) I'm still ahead decided to call. This strikes me as a pretty questionable call, though. Who mucks here?

River plays itself.

Thoughts greatly appreciated - I think playing bottom/mid pairs is one of my bigger leaks.