The Nature of Disease

Definitions

• Physiology• Function of the Body in the healthy state

• Pathology = From the Greek for Pathos meaning Disease

• Deals with the study of the structural and functional changes in cells, tissues and organs of the body that cause or are caused by disease

• Pathophysiology• Focuses on the mechanisms of the underlying disease

and provides the background for preventive as well as therapeutic health care measures and practices

The Nature of Disease

• Disease = an unhealthy state caused by the effect of injury

• Acute Disease = arises rapidly, lasts a short time

• Chronic Disease = usually begins slowly• Has signs and symptoms• Persists for a long time• Can’t be cured by medication

Sign versus Symptom

• Symptom• A subjective complaint that is noted by

the person with a disorder

• Sign• A manifestation that is noted by an

observer

• Syndrome• A collection of clinical signs, symptoms and

data

Etiology

• The cause or set of causes of a disease or condition.

Etiologic Factors • Biological Agents

• Bacteria, viruses

• Physical Forces• Trauma, burns, radiation

• Chemical Agents• Poisons, alcohol

• Nutritional Excesses of Deficits

• Most diseases are multi-factorial in origins• Risk Factors

• For example, heart disease or cancer

Idiopathic versus Iatrogenic

• Idiopathic• If etiology is unknown the disease is

said to be idiopathic

• Iatrogenic• If the disease is a byproduct of medical

diagnosis or treatment• iatros = for physician

Diagnosis versus Differential

• Diagnosis• The designation as the the nature or cause

of a health problem• Requires history and physical examination

• Differential Diagnosis• A systematic method used to identify

unknowns. This method is essentially a process of elimination

Diagnosis

• Normality• An important factor when interpreting diagnostic

test results is the determination of whether they are normal or abnormal

• Within normal Range• Not always accurate or appropriate

• Reliability• The extent to which an observation is repeatable

• Validity• The extent to which a measurement tool

measures what is intended to measure

DiagnosisSensitivity

The proportion of people with a disease who are positive for that disease on a given test or observation (e.g., Patient is 99% positive for the disease)

SpecificityThe proportion of people without the disease who are negative on a given test or observation

95% accurate v. 100%

Prevalence on Tests

• Prevalence• The number of persons who have the

disease at any given time

• Incidence• The number of new cases per year

Mortality versus Morbidity

• Mortality• Death statistics

• Morbidity• The effects of an illness has on a person’s life

• Concerned not only with the occurrence and incidence of the diseases but also the long-term impact of the disease

Prognosis• Prognosis is the probable outcome

and prospect of recovery from a disease

Levels of Prevention

• Primary• Keeping disease from occurring by removing risk

factors

• Secondary• Detect disease early when it is still asymptomatic

• Pap smears

• Tertiary• Clinical interventions that prevent further

deterioration or reduces the complication of a disease once it is diagnosed