O
oat cell carcinoma histological subtype of small cell carcinoma most commonly of bronchogenic epithelium. It accounts for approximately 20% of all lung cancers and is characterized by rapid growth (doubling time approximately 29 days). The highest incidence is in smokers. The lung primary may present with cough, haemoptysis, recurrent pneumonia, increasing breathlessness and weight loss or may be an incidental finding on chest X-ray. Therapy generally does not include surgery, but 90% are sensitive to chemotherapy, which is usually the treatment of choice.
objective associated with things external to oneself.
objective signs those which the observer notes, as distinct from the symptoms of which the patient complains.
oblique fracture a break in bone continuity that is at an angle to the main shaft of the bone.
oblique incidence when a radiotherapy beam enters the patient at an angle other than 90° due to the curvature of the skin surface.
observational study research in which the researcher observes, listens and records the events of concern. Where the researcher participates and has a role it is termed a participant observational study. May be used in qualitative social science research.
obstetrician a qualified doctor who practices the science and art of obstetrics.
obstetrics the science dealing with the care of the pregnant woman during the antenatal, parturient and puerperal stages; midwifery.
obturator that which closes an aperture.
obturator foramen the opening in the innominate bone which is closed by muscles and fascia.
occipital associated with the back of the head.
occipital bone the bone forming the back and part of the base of the skull, characterized by a large hole through which the spinal cord passes.
occipitoanterior describes a presentation when the fetal occiput lies in the anterior half of the maternal pelvis.
occipitofrontal associated with the occiput and forehead.
occipitoposterior describes a presentation when the fetal occiput is in the posterior half of the maternal pelvis.
occiput the posterior region of the skull.
occlusal biting edge of the teeth.
occlusal film a radiographic film in a waterproof envelope which the patient bites on, used to demonstrate either upper or lower 321123 on a single film.
occlusion the closure of an opening, especially of ducts or blood vessels. In dentistry, the contact of the upper and lower teeth in any jaw position. See also centric occlusion, traumatic occlusion.
occult blood blood that is not obvious on examination, detected by a chemical test, microscopic or spectroscopic examination.
occupational disease see industrial disease.
occupational exposure job-related risk of exposure to carcinogens.
occupational health the active and proactive management of health in the workplace.
OCR (Optical Character Recognition) a means of the computer directly reading printed or written characters.
ocular associated with the eye.
oculomotor the third pair of cranial nerves which innervate four of the extrinsic muscles and the upper eye lid. They also alter the shape of the lens and control pupil size.
odontoid process a peg-like projection of the axis (second cervical vertebra).
oedema abnormal infiltration of tissues with fluid. There are many causes, including reduced blood albumin, disease of the cardiopulmonary system, the urinary system and the liver. See also angio-oedema, ascites.
oesophageal associated with the oesophagus.
oesophageal atresia a narrowing of the oesophagus which is often associated with a tracheo-oesophageal fistula.
oesophageal ulcer ulceration of the oesophagus due to gastro-oesophageal reflux caused by hiatus hernia.
oesophageal varices varicosity of the veins in the lower oesophagus due to portal hypertension. These varices can bleed and may cause a massive haematemesis.
oesophagostomy a surgically established fistula between the oesophagus and the skin in the root of the neck. May be used temporarily for feeding after excision of the pharynx for malignant disease.
oesophagus the musculomembranous canal, 23cm in length, extending from the pharynx to the stomach.
oestradiol (estradiol) an endogenous oestrogen secreted by the corpus luteum.
oestriol (estriol) an endogenous oestrogen. Produced by the fetus and placenta. Oestriol levels in maternal blood or urine can be used to assess fetal well-being and placental function.
oestrogens (estrogens) a generic term referring to a group of steroid hormones, oestradiol, oestriol and oestrone. Produced by the ovaries, placenta, testes and, in smaller amounts, the adrenal cortex in both sexes. Oestrogens influence normal skeletal growth especially in puberty and are responsible for female secondary sexual characteristics and the development and proper functioning of the female genital organs. Used in the combined oral contraceptive and as hormone replacement.
oestrone (estrone) an endogenous oestrogen.
off-centre field of view in magnetic resonance imaging a field of view that is not centred at the isocentre of the magnet.
ohm the unit of electrical resistance equal to the resistance between two points on a conductor when a potential difference of one volt between the points, produces a current of one ampere.
Ohm’s law the current flowing through a conductor is proportional to the potential difference which exists across it providing other physical conditions remain constant.
olecranon process the large process at the upper end of the ulna; it forms the point of the elbow when the arm is flexed.
olfactory associated with the sense of smell.
olfactory nerve the first pair of cranial nerves. They carry sensory impulses from the olfactory epithelium of the nose to the brain.
oligodactyly a developmental absence of one or more digits (fingers or toes). There is total absence of all parts of the digit, for example, metatarsals and all phalanges.
oligodendrocyte a neuroglial cell of the central nervous system.
oligodendroglioma a slow-growing tumour most commonly of the frontal lobe of the brain, may become more aggressive after many years.
oligospermia a diminished output of spermatozoa.
omentum a sling-like fold of peritoneum. The functions of the omentum are support and protection, limiting infection and fat storage. greater omentum the fold which hangs from the lower border of the stomach and covers the front of the intestines. lesser omentum a smaller fold, passing between the transverse fissure of the liver and the lesser curvature of the stomach.
omphalocele congenital herniation of the gut through the abdominal wall around the umbilicus which is associated with chromosomal abnormality.
oncogene an altered gene that contributes to cancer development.
oncogenic capable of tumour production.
oncology the scientific study and therapy of neoplastic growths.
one-tailed hypothesis a theory that predicts a particular outcome.
oogenesis the formation of oocytes in the ovary. See also gametogenesis.
oophorectomy the surgical removal of an ovary.
oophoropexy the surgical fixation of a displaced ovary to the abdominal wall or the inferior body of the uterus, can be done prior to radiotherapy treatment so that the ovary can be protected from receiving a large dose of radiation.
opacity the incident light over the transmitted light and is a measure of the effect the radiograph has on the original light shining on it.
open (compound) fracture there is a wound permitting communication of broken bone end with air.
open reduction the realigning of fractures using a surgical procedure.
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