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Medical
Glossary


A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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 apnoea

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 faeces 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

Oedema

abnormal build-up of fluid in the body, which may cause visible swelling

Oesophageal spasm

irregular contractions of the muscles in the oesophagus, which lead to difficulty swallowing

Oesophageal varices

swollen veins in the lower oesophagus and possibly the upper part of the stomach; can cause vomiting of blood and passing of black stool

Oesophagus

a tube-shaped canal in the digestive tract, connecting the throat to the stomach

Oestrogen

a group of hormones (produced mainly in the ovaries) that are necessary for female sexual development and reproductive functioning

Oestrogen replacement therapy

treatment with synthetic estrogens drugs to relieve symptoms of menopause and to help protect women against osteoporosis and heart disease

Olfactory nerves

nerves that play a role in the sense of smell

Oligodendroglioma

a rare type of cancerous brain tumour that occurs most commonly in the cerebrum

Oligohydramnios

an unusually small amount of amniotic fluid surrounding the foetus 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 tumours

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 specialises 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

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

Optician

a person who specialises in the making and adjustment of eyeglasses and contact lenses

Oral contraceptives

drugs taken in pill form to prevent pregnancy; contain synthetic progesterone and oestrogen hormones

Orbit

the socket in the skull that contains the eyeball, along with its blood vessels, nerves, and muscles

Orchidectomy

the surgical removal of one or both of the testicles

Orchidopexy

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

Orthopnoea

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 tumour 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 tumour

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 tumour

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

Otorrhoea

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 oestrogen and progesterone

Over-the-counter remedy

a medication that can be purchased without a physician's prescription

Overactive thyroid

Overactive thyroid is the familiar term for hyperthyroidism which means that the thyroid gland produces excess levels of thyroid hormones resulting in a raised metabolism.

Overdose

an excessively large dose of a drug, which can lead to coma and death

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 colourless, odourless, 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 ageing 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

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