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Glossary - O

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  • Observation

    (OB-ser-VAY-shun)

    In medicine, watching a patient’s condition but not giving treatment unless symptoms appear or change.

  • Oncologist

    (on-KAH-loh-jist)

    A doctor with special training in the diagnosis and treatment of cancer. A pediatric oncologist is a doctor who specializes in children's cancers.

  • Oncology

    on-KAH-loh-jee

    The branch of medicine concerned with the diagnosis and treatment of cancer.

  • Operating room

    Surgical site.

  • Ophthalmologist

    OF-thul-MAH-loh-jist

    A medical doctor who specializes in diseases of the eye.

  • Opioid

    (OH-pee-OYD)

    A substance used to treat moderate to severe pain. Opioids are like opiates, such as morphine and codeine, but are not made from opium. Opioids bind to opioid receptors in the central nervous system. Opioids used to be called narcotics. An opioid is a type of alkaloid.

  • Optical

    Pertaining to the sense of sight or to the eyes.

  • Organ

    (OR-gun)

    Several tissues grouped together to perform one or more functions in the body.

  • Organism

    (OR-guh-NIH-zum)

    Any living thing.

  • Orgasm

    (OR-ga-zum)

    The final part of the sex act, which involves contraction of sexual organs and a sudden release of endorphins, leading to a feeling of pleasure. In males, orgasm usually occurs with release of semen.

  • Orthopedic surgeon

    (OR-thuh-PEE-dik SER-jun)

    A surgeon who specializes in diseases and injuries of the bones.

  • Osteomyelitis

    Infection of bone.

  • Osteoporosis

    (OS-tee-oh-puh-ROH-sis)

    A condition in which there is a decrease in the amount and thickness of bone tissue. This causes the bones to become weak and break more easily. Osteoporosis may be caused by older age, hormone changes, taking certain medicines, and not eating enough foods with calcium and vitamin D. It may also be caused by certain types of cancer and cancer treatment.

  • Osteosarcoma

    OS-tee-oh-sar-KOH-muh

    A cancer of the bone that usually affects the large bones of the arm or leg. It occurs most commonly in young people and affects more males than females. Also called osteogenic sarcoma.

  • Otic

    Relating to the ear.

  • Otitis

    Ear infection.

  • Ovaries

    (OH-vuh-rees)

    A pair of female glands in which the eggs form and the female hormones estrogen and progesterone are made. These hormones play an important role in female traits, such as breast development, body shape, and body hair. They are also involved in the menstrual cycle, fertility, and pregnancy. There is one ovary on each side of the uterus.

  • Over-the-counter

    (OH-ver-the-KOWN-ter)

    Refers to a medicine that can be bought without a prescription (doctor's order). Examples include analgesics (pain relievers), such as aspirin and acetaminophen. Also called nonprescription and OTC.

  • Oxygen

    (OK-sih-jen)

    A colorless, odorless gas. It is needed for animal and plant life. Oxygen that is breathed in enters the blood from the lungs and travels to the tissues.

  • Oxygen mask

    An implement to enable breathing.