AMA Medical Glossary
O
Oat cell carcinoma- another term for small-cell carcinoma
Obesity- a condition in which there is an excess of body fat; used to describe those who weigh at least 20 percent more than the maximum amount considered normal for their age, sex, and height
Obsessive-compulsive disorder- a mental disorder in which a person is obsessed with certain thoughts, leading them to repeatedly perform specific acts; for example, constantly washing the hands out of fear of germs and dirt
Obstructive sleep apnea- the blockage of the airways during sleep, which causes breathing to stop for very short periods of time, commonly caused by excessive relaxation of muscles at the back of the throat
Occlusion- the blocking of an opening or passageway in the body
Occult blood- blood in the feces that can be detected only by chemical tests
Occupational disease- a disease that occurs as a result of factors in the workplace
Occupational therapy- treatment to relearn physical skills lost as a result of an illness or accident
Ocular- describes something related to the eyes
Oculomotor nerves- nerves that stimulate movement of the eyeball
Olfactory nerves- nerves that play a role in the sense of smell
Oligodendroglioma- a rare type of cancerous brain tumor that occurs most commonly in the cerebrum
Oligohydramnios- an unusually small amount of amniotic fluid surrounding the fetus in the uterus, which can lead to complications with the pregnancy
Oligospermia- a low level of sperm in the semen; one of the main causes of infertility in men
Oncogenes- genes that, when altered by environmental factors or viruses, can cause abnormal cell growth
Oocyte- an egg cell that has not developed completely
Oophorectomy- the surgical removal of one or both ovaries; used to treat the growth of ovarian cysts or tumors
Open heart surgery- any operation in which the heart is stopped temporarily and a machine is used to take over its function of pumping blood throughout the body
Ophthalmia- severe inflammation of the eyes
Ophthalmologist- a doctor who specializes in care of the eyes; treats eye diseases and disorders
Ophthalmoplegia- partial or total loss of the ability to move the eyes
Ophthalmoscopy- examination of the inside of the eye using a lighted viewing instrument
Opportunistic infection- infection by organisms that would be harmless to a healthy person, but cause infection in those with a weakened immune system (for example, persons with AIDS or chemotherapy patients)
Optic- pertaining to the eyes
Optician- a person who specializes in the making and adjustment of eyeglasses and contact lenses
Optic nerves- the pair of nerves that carry visual information from the retina to the brain
Optic neuritis- inflammation of the optic nerve, often causing a partial loss of vision
Oral contraceptives- drugs taken in pill form to prevent pregnancy; contain synthetic progesterone and estrogen hormones
Orbit- the socket in the skull that contains the eyeball, along with its blood vessels, nerves, and muscles
Orchiectomy- the surgical removal of one or both of the testicles
Orchiopexy- an operation to correct an undescended testicle
Orchitis- inflammation of a testicle, which can be caused by infection with the mumps virus
Organ donation- an agreement to allow one or more organs to be removed and transplanted into someone else
Organism- any single, functioning form of life
Orgasm- involuntary contraction of genital muscles experienced at the peak of sexual excitement
Orphan drugs- drugs used to treat rare diseases; not normally produced because potential sales are small
Orthopnea- breathing difficulty experienced while lying flat; can be a symptom of heart failure or asthma
Orthotic- a device used to correct or control deformed bones, muscles, or joints
Osgood-Schlatter disease- painful enlargement and inflammation of the area of the shinbone just below the knee, usually occurring in adolescent boys
Osmosis- the process of passage of the solvent portion of a lesser-concentrated solution through a semipermeable membrane into a higher-concentrated solution until the two solutions are equal in concentration; plays an important role in water distribution in the body
Ossification- the formation and maintenance of bone
Osteitis- inflammation of bone
Osteitis deformans- another name for Paget's disease
Osteoarthritis- see Degenerative arthritis
Osteoblast- a cell that forms bone
Osteochondritis dissecans- bone degeneration inside of a joint, causing small pieces of bone and cartilage to become detached
Osteochondritis juvenilis- inflammation of a growing section of bone in a child or adolescent
Osteochondroma- a noncancerous tumor made up of bone and cartilage
Osteoclast- a cell that breaks down unwanted bone tissue; also refers to a device for fracturing a bone to correct a deformity
Osteodystrophy- defective bone formation
Osteogenesis imperfecta- a genetic disorder in which bones are abnormally fragile, leading to multiple breaks and deformity
Osteolysis- the softening and destruction of bone
Osteoma- a noncancerous bone tumor
Osteomalacia- the loss of minerals and softening of bones because of a lack of vitamin D; called rickets in children
Osteomyelitis- the inflammation of bones and bone marrow because of an infection, usually caused by bacteria
Osteopetrosis- a rare hereditary disorder in which bones become harder and more dense, causing them to break more easily
Osteophyte- an outgrowth of bone near a joint
Osteoporosis- a condition in which bones become less dense, more brittle, and fracture easily
Osteosarcoma- a cancerous bone tumor
Osteosclerosis- an abnormal increase in density and hardness of bone
Otalgia- the medical term for an earache
OTC remedy- see Over-the-counter remedy
Otitis externa- inflammation of the outer ear due to an infection; commonly called swimmer's ear
Otitis media- inflammation of the middle ear (between the eardrum and inner ear) because of the spread of an infection from the nose, sinuses, and throat
Otorrhea- a discharge from an inflamed ear
Otosclerosis- progressive deafness caused by bone formation around structures in the middle ear
Ototoxicity- harmful effect that some drugs have on the organs or nerves in the ears, which can lead to hearing and balance problems
Outpatient treatment- medical attention that does not include an overnight stay at a hospital
Ovaries- two almond-shaped glands located at the opening of the fallopian tubes on both sides of the uterus; produce eggs and the sex hormones estrogen and progesterone
Overdose- an excessively large dose of a drug, which can lead to coma and death
Over-the-counter remedy- a medication that can be purchased without a physician's prescription
Ovulation- the development and release of the egg from the ovary, which usually occurs halfway through a woman's menstrual cycle
Ovum- another term for an egg cell
Oxidation- a chemical reaction involving active sources of oxygen (called oxygen free radicals) that damages cells
Oximetry- determination of the amount of oxygen in the blood by measuring the amount of light transmitted through an area of skin
Oxygen- a gas that is colorless, odorless, and tasteless; essential to almost all forms of life
Oxygen free radicals- active forms of oxygen found in pollution, cigarette smoke, and radiation that can damage cells and are believed to play a role in the aging process and cancer
Oxytocin- a hormone produced in the pituitary gland that causes contraction of the uterus during childbirth and stimulation of milk flow during breast-feeding Ozone- a poisonous form of oxygen that is present in the earth's upper atmosphere, where it helps to screen the earth from damaging ultraviolet rays