Bma Illustrated Medical Dictionary

after ovulation, releases progesterone

during the 2nd half of the cycle.

After its release, the ovum travels along

the fallopian tubeand, if fertilizationdoes

not occur, is shed during menstruation.

Regular menstruation usually means that

ovulation is occurring, except around

pubertyand approaching the menopause.

ovumThe egg cell (female cell of repro-

duction). An ovum contains a nucleus

suspended in cytoplasm (a gel-like sub-

stance) and is surrounded by a protective

layer, the zona pellucida.

About 1 millionimmature ova are pre-

sent in each ovaryat birth, but only

about 200 per ovary mature to be

released at ovulation. A fertilizedovum

develops into an embryo.

oxazepamA benzodiazepine drugused

as a short-term treatment for anxiety.

Oxazepam may cause dependence if it

is taken regularly for more than 2 weeks

(see drug dependence).

oximeterAn instrument used for mea-

suring the oxygen content of the blood.

oxprenololA beta-blocker drugthat is

used in the treatment of hypertension,

angina, and cardiacarrhythmias. Ox-

prenolol may also be used to relieve

symptoms of anxietyand control those

of hyperthyroidism.

oxybutyninA drug that is used to treat

frequent urination (see urination, fre-

quent) by increasing the bladder’s

capacity. Common side effects include

dry mouth and blurred vision.

oxygenA colourless, odourless gas that

makes up 21 per cent of the Earth’s atmo-

sphere. Oxygen is essential for almost all

forms of life, including humans, because

it is necessary for the metabolic “burn-

ing” of foods to produce energy – a

process that takes place in body cells

and is known as aerobicmetabolism.

Oxygen is absorbed through the lungs

and into the blood, where it binds to

the haemoglobinin red blood cells. As

oxygen-rich blood circulates around the

body, the oxygen is released from the

red blood cells into the body tissues.

Additional supplies of oxygen are used

to treat conditions such as severe bron-

chitisor hypoxia. High-pressure oxygen

(see hyperbaric oxygen treatment) is

sometimes used to treat decompression

sicknessor carbon monoxidepoisoning.

(See also ozone.)

oxygen concentrator An appliance

used in oxygen therapythat separates

oxygen from the air and mixes it back in

at a greater concentration. This oxygen-

enriched air is delivered through a tube

for prolonged inhalation. The appliance

is used by people who have persistent

hypoxiadue to severe chronic obstruc-

tive pulmonary disease (see pulmonary

disease, chronic obstructive). (See also

hyperbaric oxygen treatment.)

oxygen therapyThe process of supply-

ing a person with oxygen-enriched air

to relieve severe hypoxia(inadequate

OVUM OXYGEN THERAPY

O

Nasal

cannulas

Oxygen tube

Oxygen

concentrator

OXYGEN THERAPY

Humidifier

keeps the

oxygen

moist

HOME OXYGEN THERAPY

Nucleus

Cytoplasm

Zona pellucida

Cell from

ovarian follicle

OVUM