MD80 CREW EXECUTED AN EMER DSCNT WHEN CABIN PRESSURIZATION WAS LOST.

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LOSS OF CABIN PRESSURIZATION. LEVEL AT FL330 AND CABIN BEGAN SLOW CLB TO ABOVE 10000 FT. DID NOT NOTICE ANYTHING UNUSUAL UNTIL CABIN ALT HORN SOUNDED. CABIN ALT STABILIZED AT 10500 FT; AS WE RAN THE RAPID DEPRESSURIZATION CHKLIST. WE WERE UNABLE TO LOWER THE CABIN ALT AND EXECUTED THE EXPLOSIVE DEPRESSURIZATION CHKLIST. DECLARED EMER WITH CTR AND AFTER BEGINNING OUR DSCNT WE WERE ABLE TO POSITIVELY CTL THE CABIN ALT WITH THE MANUAL CTLR. I ELECTED TO LEVEL THE ACFT AT FL200 FOR FUEL CONSIDERATIONS AND WE WERE ABLE TO ASSESS THAT THE PAX AND THE CABIN AREA WERE OK. DURING OUR DSCNT; WE INITIALLY BROUGHT THE CABIN DOWN TO 1000 FT THEN SLOWLY RAISED IT BACK UP TO 3000 FT FOR PAX COMFORT. FLT ATTENDANT #1 AGAIN RPTED NO ADVERSE REACTIONS TO PAX DUE TO SHORT EXPOSURE ABOVE 10000 FT SO WE CONTINUED TO OUR DEST. COORDINATED EMER PROCS WITH DISPATCH; BNA OPS AND BNA MAINT DURING DSCNT. ALSO USED JUMP SEATER TO MANUALLY CTL PRESSURIZATION DURING DSCNT AND LNDG PHASE. TERMINATED EMER WITH BNA APCH WHEN BELOW 10000 FT. LANDED WITHOUT FURTHER EVENT AT BNA.