Dr. Estrella is a Doctor of Medicine graduate from the University of the Philippines (UP) College of Medicine Batch 1955. He started his career as an Adjunct Resident of the Department of Gynecology in PGH in the same year.
After serving UP Manila as a professor and a consultant for nearly 40 years, he got the position of Vice-Chancellor for Administration in 1985. The following year, he became the Director of PGH. He held the said position for 8 year, from Semptember 1986 to October 1994.
During his term, the PGH was cited in 1994 as one of the "33 Centers of Excellence in Government Service" by the Senate Civil Service Committee that was chaired then by Senator Blas F. Ople.
While attending to his tasks as PGH administrator, Dr. Estrella was also a COnsultant to the Senate President, Senate-Manila and Special Adviser to the University President at UP Diliman.
After he retired from PGH, he was a consultant to the Department of Obstetrics and Gynecology of the Medical City. He joined the Medical City as its Director of Medical Services in February 1995. He also worked as a Consultant to the Office of Senator Edgardo Angara (September 1995), Euromed Laboratories, Philippines (November 1995), and UP Health Services (January to December 1997).
Dr. Estrella has attended post graduate training and education courses at the Radium Hemment in Stockholm, Sweden; the Memorial Hospital for cancer and Allied Diseases in New York, USA; the University of Vienna, Austria; and the Harvard Medical School, Harvard University, Massachusetts, USA.
He also won awards such as the 1997 Gawad Propesyonal sa Medisina from the UP Manila Alumnia Association and the 1992 Presidential or Lingkod Bayan Award.