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Johannes Karl Martensson, M.D., Ph.D.

Johannes Karl Martensson obtained his MD at the University Medical School in Uppsala and Linkoping and his PhD (in Biochemistry) at Linkoping University Medical School, in Sweden. He came to the USA as a Visiting Professor in Biochemistry at Cornell University Medical Collage, New York, in 1986. He was promoted to Associate Professor in Biochemistry and has 58 full-length publications, including 8 publications in the Proceeding of National Academy of Sciences on the importance of glutathione and vitamin C in anti-oxidant defenses, mitochondrial function and cell death.


He completed his Internal Medicine Residency at Greenwich Hospital/Yale University Medical School and his Gastroenterology Fellowship at Thomas Jefferson University Hospital and Pennsylvania Hospital, Philadelphia.


He moved to Citrus County in 1996 to join Citrus Gastroenterology and Fernando Bueno MD. He continues to enjoy working in this vibrant community, full of challenging medical conditions and patients in need. He has a specific interest in risk factors of cancer development and treatment, inflammatory bowel disease, bile duct and liver diseases, inflammatory conditions related to GERD and Esophageal cancer and functional disorders related to previous gastro-intestinal surgery. He is an advocate for preventive medicine and enjoys many of the outdoor activities found in this beautiful part of Florida. He is part-owner in Suncoast Endoscopy, Inverness, an efficient out-patient surgical center, and he is on staff at both Citrus Memorial Hospital and Seven River Regional Medical Center.

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Elaine Whyte, Ph.D., RN, MSN, FNP-C

Completed nursing degree in Dundee Scotland where I was born and raised. Moved to Texas after working with US Dept. of the Navy. Completed Masters in Nursing and Family Nurse Practitioner. Certification at West Texas A&M University. Completed PhD in Nursing Science at Texas Woman's University in Denton Texas. Loves nature and all things Disney. Has two furry companions who follow her everywhere.

View Curriculum Vitae (CV) Here
Our Office Staff

Here at Citrus Gastroenterology, PA, our entire staff believes excellent medical care is about heartfelt caring and compassion. That is why you’ll feel comfortable from the moment you walk in. You’ll appreciate a staff who knows you by name and doctors who treat you like family.

Citrus Gastroenterology, PA accepts most major insurance plans. Please call our Main (Inverness) office at 352.344.8080 for more details or to schedule an appointment. We look forward to helping you live a happier, healthier life.