FO REPORTS DISTRACTION BY FA MEDICAL EMERGENCY CALL DURING APPROACH AND ALLOWS ACFT TO DESCEND BELOW MSA.

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DURING RADAR VECTORS FOR THE ILS; THE 'A' FLT ATTENDANT CALLED TO SAY SHE HAD A MEDICAL EMER. I WAS THE PF; SO THE CAPT TOOK THE FLT ATTENDANT'S CALL AND I TOOK OVER THE RADIOS AND CONTINUED FLYING/MONITORING THE AUTOPLT. WE WERE JUST LEVELING AT 3000 FT MSL; HDG 060 DEGS; WHEN THE FLT ATTENDANT CALLED. ATC CALLED AND GAVE US A HDG 030 DEGS TO INTERCEPT THE LOC; AT WHICH TIME I TURNED THE HDG BUG 030 DEGS AND RESPONDED TO ATC. DURING THAT TIME AND THE DISTR OF THE MEDICAL EMER; I FAILED TO MONITOR THE AUTOPLT'S PROGRESS AND THE PLANE DSNDED BEYOND 3000 FT MSL UNTIL THE CTLR SAID SHE HAD A LOW ALT ALERT AND WE SIMULTANEOUSLY RECEIVED A GPWS TERRAIN ALERT. I IMMEDIATELY APPLIED FULL PWR AND PITCHED UP. WE LEVELED AT 3200 FT MSL AT WHICH TIME THE CTLR ASKED FOR OUR ALT AND THEN CLRED US FOR THE APCH. WE WERE UNABLE TO GET THE AUTOPLT OR THE FLT DIRECTOR TO CAPTURE THE LOC OR GS; SO I FLEW THE PLANE RAW DATA DOWN TO AN UNEVENTFUL LNDG. LESSON LEARNED: NEVER LET EXTRANEOUS EVENTS -- EVEN WHAT SEEM URGENT AT THE TIME -- DISTRACT FROM FLYING THE PLANE/MONITORING THE AUTOPLT'S PROGRESS IN A CRITICAL PHASE OF FLT.