Stomach problem introduced by a medic from the east (6)
I believe the answer is:
omasum
'stomach' is the definition.
(I know that omasum is a type of stomach)
'problem introduced by a medic from the east' is the wordplay.
'problem' becomes 'sum' (as in a mathematical problem).
'introduced by' is a charade indicator (letters next to each other).
'medic' becomes 'mo' (medical officer).
'from the east' says the letters should be written backwards (on a map from right to left).
'a'+'mo'='amo'
'amo' back-to-front is 'oma'.
'sum' put after 'oma' is 'OMASUM'.
(Other definitions for omasum that I've seen before include "bible for a 17 [RUMINANBT]" , "The third gut" , "Ruminant's third stomach" , "Cow's third stomach" .)