American doctor on course read up about certain glands (7)
I believe the answer is:
adrenal
'about certain glands' is the definition.
(as in the adrenal glands)
'american doctor on course read up' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'doctor' becomes 'Dr' (abbreviation).
'on course' becomes 'lane' (a lane is a path or course. I am not sure about the 'on' bit.).
'read up' is a reversal indicator (I've seen 'reading up' mean this (in a down clue, letters go up)).
'lane' backwards is 'enal'.
'a'+'dr'+'enal'='ADRENAL'
(Other definitions for adrenal that I've seen before include "close to the kidneys!" , "Relating to glands near the kidneys" , "Gland that secretes the fight or flight hormone" , "Glandular" , "(Gland) on the kidney" .)