Biology of Disease

Polyploidy The situation in which the chromosome
number is an exact multiple of the haploid number
but exceeds the diploid number (seeaneuploidyand
euploidy).

Polyps Benign tumors that arise in the nose or from the
endothelium of the gastrointestinal tract.

Polyuria The production of abnormally large volumes of
urine. Compare withanuriaand oliguria.

Portals of entry Sites at whichpathogenscan enter the
body.

Portals of exit Sites at whichpathogenscan leave the
body.

Precision The ability of a test for ananalyteto give the
same result every time the same sample is analyzed.
Compare withaccuracy.

Predisposing factors Conditions or situations that make
an individual more susceptible to disease: they include
age, sex, heredity and environmental factors.

Premalignant This refers to clinical conditions that
increase the risk of the patient developing a malignant
tumor.

Prevalence The prevalence of a disease refers to the pro-
portion of people in a population affected at a specific
time.

Primary immunodeficiency diseases (PID) Clinical con-
ditions that result from a genetic defect leading to a
failure of one or more components of the immune
system (see alsosecondary immunodeficiencies).

Primary tumor Malignant tissue growing in the site where
it initially started (compare withmetastasis,second-
ary tumor).

Prognosis The likely outcome of a disease.

Programmed theory of aging Suggests that each spe-
cies has an inbuilt biological clock and that aging is a
genetically programmed series of events.

Proinflammatory Description of a number of cytokines,
which when secreted promoteinflammation.

Prophylactic bilateral mastectomy The removal of appar-
ently healthy breasts to prevent the development of
breast cancer in genetically susceptible women.

Psychogenic diseases Clinical conditions that originate in
the mind.

Ptosis An inability to raise the eyelids.

Pulmonary circulation The circuit which the blood fol-
lows between the right side of the heart, the lungs and
the leftatrium(compare withsystemic circulation).

Pulse The bulging of the arteries that can be felt at a

number of sites in the body during systole.

Purified protein derivative (PPD) A mycobacterial extract

used in the Mantoux reaction to test if an individual is

already sensitized by infection or previous vaccination

to TB.

Purkinje fibers Seebundle of His.

Pyogenic infections Infections with bacteria that cause

the formation of pus.

Recessive mutations Mutations that are only expressed in

an individual who ishomozygousfor the condition.

Recommended daily amount (RDA) This was originally

used by the UK Department of Health in 1979 to define

the amounts of certain nutrients needed by different

groups within the population.

Reference nutrient intake (RNI) An amount of a nutri-

ent that is greater than the dietary needs of 97.5%

of a population (compare with estimated average

requirement,lower reference nutrient intake and

safe intake).

Reference ranges Numerical reference limits based on the

mean value of ananalyteplus or minus two standard

deviations against which test results can be compared.

The termnormal rangeis still used synonymously

with reference range.

Reflux esophagitis A back flow of gastric juice from the

stomach into the lower end of the esophagus.

Regurgitation An imperfect closing of the heart valves

leading to leakage and backflow (compare with

stenosis).

Relapse A relapse occurs when, following a period of

apparent recovery, the symptoms of the disease

return.

Remission A period of good health with a reduction or

disappearance of symptoms following a disease; may

be permanent or temporary.

Respiratory acid–base disorder This is the occurrence of

an abnormal blood pH because of lung dysfunction.

Compare withmetabolic acid–base disorder.

Reticulocytes The immediate precursors of erythrocytes,

which have nuclei and are still able to synthesize

hemoglobin.

Retinoids Name for a group of naturally occurring as well

as many synthetic forms of vitamin A (retinol).

Reversion This occurs in some patients who do not

develop an effective immune response to an attenu-

ated vaccine and the weakened microorganisms in it

become virulent.

GLOSSARY

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