Dictionary

Body systems

Anatomy and the conditions of each body system, from the heart and lungs to the skin.

obesityHaving much more body fat than is healthy, usually defined in adults as a body mass index of 30 or higher.

obsessive-compulsive disorderA mental health condition with unwanted thoughts that keep coming back and actions a person feels driven to repeat.

obstetricianA physician who specializes in the care of people during pregnancy, labor and birth, and just after.

obstetricsThe branch of health care that looks after people during pregnancy, birth and the weeks after birth.

obstructionA blockage in a passage of the body, such as an airway, the bowel, a blood vessel or a tube.

obstructive sleep apneaA sleep disorder in which the upper airway closes again and again during sleep, stopping or reducing breathing.

occipitalRelating to the back of the head.

occipital lobeThe part of the brain at the back of the head that takes in and makes sense of what the eyes see.

occlusionA blockage or closing off of a passage, such as a blood vessel, tube or IV line.

oculomotorHaving to do with movement of the eyes; most often refers to the oculomotor nerve, the third cranial nerve.

oculomotor nerveThe third cranial nerve, which moves most of the muscles of the eye, raises the eyelid and narrows the pupil.

olfactoryRelating to the sense of smell.

oligohydramniosToo little amniotic fluid around the baby during pregnancy.

oliguriaMaking less urine than normal, in an adult below about 400 mL a day.

omega-3 fatty acidA kind of healthy unsaturated fat found in oily fish, flaxseed, walnuts and some plant oils.

oncologyThe branch of medicine that deals with cancer.

oncotic pressureThe pull that proteins in the blood, mainly albumin, exert to hold fluid inside the blood vessels.

ophthalmicHaving to do with the eye, or describing a medicine made to be put in the eye.

opportunistic infectionAn infection caused by a germ that rarely makes healthy people sick but takes advantage of a weakened immune system.

optic nerveThe nerve that carries visual signals from the back of the eye to the brain; the second cranial nerve.

oralRelating to the mouth, or taken by mouth.

oral cavityThe mouth: the space from the lips to the throat, including the teeth, gums, tongue and palate.

oral glucose tolerance testA blood test that measures blood sugar before and at set times after drinking a measured sweet glucose drink.

oral rehydration solutionA drink with a set mix of water, salts and sugar, used to replace fluid lost through diarrhea or vomiting.

organ systemA group of organs that work together to do one main job in the body.

orientationA person's awareness of who they are, where they are, what time it is and what is happening.

oropharynxThe middle part of the throat, behind the mouth, from the soft palate down to the top of the voice box.

orthopedicHaving to do with the bones, joints, muscles, ligaments and tendons, and the branch of medicine that treats them.

orthopneaDifficulty breathing when lying flat that eases when sitting or standing up.

orthostaticRelating to standing upright, or caused by changing to a standing position.

orthostatic hypotensionA drop in blood pressure when a person stands up from lying or sitting.

osmolarityThe amount of dissolved particles in a set volume of fluid, which decides which way water moves.

osmosisThe movement of water across a membrane from a less concentrated solution to a more concentrated one.

osmoticRelating to osmosis, the movement of water across a membrane toward the side with more dissolved particles.

osmotic diuresisAn increase in urine output caused by dissolved substances in the kidney tubules that hold water with them.

osteoarthritisA long-term joint disease in which the cartilage that cushions the ends of the bones wears away.

osteoclastA bone cell that breaks down and removes old bone tissue.

osteomyelitisAn infection of bone.

osteopeniaBone density that is lower than normal but not low enough to be called osteoporosis.

osteoporosisA condition in which bones lose density and become thin, weak and easy to break.

ostomyA surgically made opening from an inside organ, such as the bowel or urinary tract, through the belly wall to the outside.

otitisInflammation of the ear.

otitis externaInflammation or infection of the outer ear canal, often called swimmer's ear.

otitis mediaInflammation or infection of the middle ear, the space behind the eardrum.

outflowThe flow of a fluid out of an organ, space or vessel.

ovarian cancerCancer that starts in the ovaries or in the nearby fallopian tubes.

ovaryOne of the two small female glands beside the uterus that hold eggs and make the hormones estrogen and progesterone.

overloadMore of something than the body can handle; in nursing, most often too much fluid in the circulation.

ovulationThe release of a mature egg from an ovary, usually once in each menstrual cycle.

ovumAn egg cell: the female reproductive cell that can join with a sperm to start a pregnancy.