Pathophysiology 101-823 Unit 1 Basic Concepts of Health & Disease Paul Anderson 2011
Feb 02, 2016
Pathophysiology 101-823
Unit 1
Basic Concepts of Health & Disease
Paul Anderson 2011
2
Learning Objectives
• Describe health and disease in terms of the homeostatic model of the human body.
• Explain how disease of cells, tissues or organs affects homeostasis and relate selected disequilibria to their diseases of origin.
• Explain how homeostatic responses may cause clinical manifestations of disease.
• Define the terms etiology, physiology, pathology, pathophysiology.
• Define etiological factors and distinguish between genetic and environmental factors.
• Define multifactorial, congenital and acquired, infectious, contagious (communicable) diseases.
• Define clinical manifestations, signs, symptoms, syndrome.
• Describe the process of diagnosing diseases and requirements of good lab tests.
• Describe the clinical course & appearance of disease, defining the terms acute and chronic diseases, preclinical, clinical, subclinical and carrier.
• Compare how a disease is studied by means of epidemiology and by the study of its pathogenesis.
• Define mortality, morbidity, incidence and prevalence of diseases.
References: Porth, Pathophysiology, Ch. 1 pp. 2 - 9, Ch. 9 (Homeostasis)
Porth, Essentials, Introduction, pp. xxxi-xxxv, Ch. 7 (Homeostasis).
3
Disease and Health
What is Health?
• Health can be defined as a state of complete physical, mental and social well being, not merely the absence of disease and infirmity (World Health Organisation WHO 1948).
What is Disease?
• Disease can be defined as a recognisabledeviation from the normal structure and functioning of a body system or its components.
• Diseases may also be called Disorders.
4
How Disease affects Homeostatic Mechanisms
Disease affects Homeostatic mechanisms in 4 ways
A. Disease Disturbs Homeostasis, causing Disequilibria.B. Disease causes a Failure of Homeostatic Adaptation
i.e. failure to restore homeostasis.C. The diseased body does adapt to disequilibria caused
by disease through its homeostatic mechanisms, but sometimes Overcompensates to cause Secondary Disease.
D. Compensatory Homeostatic Responses can produceClinical Manifestations of an existing disease.
Homeostatic Control Systems are Sensitive to Changes in the Internal Environment & produce Compensatory Negative Feedback Responses.
5
A. Disease Causes Disequilibria
Disease disturbs Homeostasis Producing a State of Disequilibrium
Disease cells tissues organs
Loss of homeostatic function
damages
Disequilibrium
Glomerulonephritisepithelial cells Glomerular Epithelium Kidney
•Filtration of blood•Urine formation:
Hypertension
Heart Disease Causes Disequilibrium
Coronary Heart Disease (CHD)
Heart cells die(Myocardial Infarction)
Ventricular muscle weakened
Heart’s pumping ability declines(cardiogenic shock -a dangerous complication of CHD)
Reduced cardiac outputHypotension
Note: CHD = Coronary Artery Disease - CAD
Examples of Disequilibria
DISEQUILIBRIUM FACTOR AFFECTED POSSIBLE CAUSES
Fever - elevated body temp. Viral/bacterial infection
Edema - elevated body [H20] kidney disease(causing fluid retention)
Hypertension - elevated ABP CV or kidney disease
Hypotension - lowered ABP hemorrhage or heart disease
Hyperglycemia - elevated plasma [glucose] -"blood sugar” Diabetes mellitus
Hypoxia - lowered tissue pO2 Respiratory or CV disease
8
B. Disease causes a Failure to Maintain Homeostasis
• Diseased organs, tissues, cells cannot properly adapt to environmental changes and maintain homeostasis.
• With disease there is therefore a tendency for persistence of disequilibria that may lead to other disequilibria and secondary disease.
• Thus in Diabetes mellitus, chronic hyperglycemia with disordered metabolism causes further disequilibriasuch as dehydration and ketoacidosis.
• Complications of diabetes from secondary diseasesare superficial infections and diseases of the eyes, kidneys, nerves and arteries.
Disturbance to Homeostasis
Adaptation
Health Diseasenormal abnormal
Adaptations to Homeostatic Imbalance in Health & Disease
•Healthy Adaptation is Homeostatic, restoring normal equilibrium and health.
•In Disease there is a Failure of Normal Adaptationcausing persistent disequilibrium leading to other disequilibria and secondary disease.
•Disequilibrium removed•Homeostasis restored
•Disequilibrium remains•Further disequilibria may occur•Secondary disease may occur
Local Adaptations to Environmental Change
Increased Workload on
Heart
Local (Cellular)Adaptation
Health Disease
Normal Hypertrophy increases cardiac output & reduces stress on heart muscle
Abnormal Hypertrophy may cause decline in cardiac output
Local Adaptations to Environmental Change are Cellular•myocardial hypertrophy in an athlete (normal): cells increase insize uniformly.•myocardial hypertrophy in hypertensive patient (abnormal): cellsincrease in size abnormally (width more than length)
Exercise causes increased oxygen demands by muscles
Chronic hypertension means heart must generate higher pressure to eject blood
Porth fig 5-2
11
Systemic Adaptations to Environmental Change
Hyperglycemia
Systemic Adaptation
Health DiseaseNormal blood sugar level restored
•Hyperglycemia remains•Further disequilibria may occur (e.g. ketoacidosis, dehydration)
•Secondary disease may occur (in skin, eyes, kidneys, nerves, arteries)
Systemic Adaptations to Environmental Change involvesHomeostatic Control Systems
• Restoring the blood sugar level to normal after a meal via the insulin response in a healthy person.
• Failure to restore the blood sugar level in the absence of an insulin response in a diabetic person and shifting of metabolism to fat & protein breakdown.
Blood sugar level rises after a meal
Blood sugar level is high due to pancreatic β cell dysfunction or because of insulin resistance
12
C. Disease Caused by Homeostatic Overcompensation
The body adapts to stress from one disease through its homeostatic mechanisms, sometimes Overcompensating to cause a Secondary Disease
Chronic Systemic Hypertension
Increased workload on left ventricle
Left ventricle hypertrophies
Cardiac Arrythmia
Decreased cardiac output
In this example a local (cellular) adaptive response of cardiac muscle results in overcompensation.
Overcompensation may eventually cause
Porth fig 5-2
13
D. Homeostatic Responses Produce Clinical Manifestations
Stimulus Receptor
Integrating Center
EffectorCompensatory Homeostatic Response
Negative feedbacknormallyturns off stimulus
ClinicalManifestation of Disease
Disease
Disequilibrium
Homeostatic Responses can cause Clinical Manifestations of a Disease
acts as activates
Sendsmessage to
Sends message to
causes
Compensatory Responses may Persist in Disease State giving Clinical Manifestations
may cause
14
Clinical Manifestation of Hemorrhage
Hypotension Arterial Baroreceptors
Cardiac Accelerator Center of hind brain
TachycardiaClinical Manifestation (Sign) of Disease
Negative feedback
Disease or Injury
Blood Volume
Homeostatic responses can causeClinical Manifestations of a Disease.
Compensatory Homeostatic ResponseIncreased heart activity
Causes acute hemorrhage
15
Definition of Pathophysiology - 1
• Pathology is concerned mainly with studying the characteristics of diseased organs & tissues.
• Physiology is the study of normal body function.
• Pathophysiology is the study of the physiological changes associated with disease.
Pathophysiology is a combination of Pathology and Physiology
Pathophysiology is the Physiology of Disease
Disturbance to Homeostasis
Adaptation
Health Disease
Local (Cellular)
Systemic (Homeostatic Control System)
Pathology
Pathophysiology
Physiology
normal abnormal
studies Studiesdiseased organs & tissues Studies the
physiology of disease
combination of pathology & physiology
Definition of Pathophysiology - 2
17
Focus & Usefulness of Pathophysiology
Since structure and function go together pathophysiologymust deal with
• Structural changes due to disease in organs, tissues and cells
• Effects these structural changes have on body functions.
Therefore Pathophysiology
• Focuses on the mechanisms underlying disease but also
• Provides a background for therapeutic health caremeasures and practices.
Pathophysiology is the Physiology of Disease
Therefore Pathophysiology helps nurses understand disease processes & how nursing interventions can restore health.
18
What Pathophysiology Includes
Pathophysiology studies the disease in the individual so includes:
• Etiology
• Clinical Manifestations & diagnosis
• Pathogenesis & Clinical Course of disease
• Treatment & Management of Disease
19
Etiology
• Environmental Factors– Microorganisms, viruses, bacteria & other parasites– Physical factors, physical trauma, radiation, etc– Chemical agents, drugs, toxins– Nutritional excess or deficit– Psychological stressors (causing maladaptive responses to stress
e.g. Post Traumatic Stress Disorder)
• Genetic Factors– Inherited gene or chromosomal mutations (alterations to DNA)
Etiology is the the study of the causes of disease
�Etiological factors are factors that cause disease �Etiological factors may be Environmental or Genetic
Diseases may be genetic, environmental or multifactorial(caused by a combination of genetic & environmental factors).
20
Genetic Factors may cause Genetic Disease or a Genetic Predisposition to develop a disease.
Etiology: Genetic & Multifactorial Disease
• Genetic Disease may be caused by a single gene defect(e.g. cystic fibrosis, sickle cell anemia), by many genes or by a chromosomal defect (e.g. Down syndrome).
• Diseases involving a Genetic Predisposition are associated with many genetic factors (inheritance of certain genes) and environmental factors (lifestyle etc.) called “Risk Factors” .
• These diseases are therefore called MultifactorialDiseases and include some congenital diseases, heart disease, diabetes mellitus 2, hypertension, cancer, manic depressive psychosis (bipolar disorder) and schizophrenia.
Most Diseases are Multifactorial
21
Congenital vs Acquired Conditions
Environmental Factors may cause congenital or acquired disease.
• Congenital Conditions are present at birth.
• Congenital Conditions may be genetic (e.g. cystic fibrosis) environmental (e.g. fetal alcohol syndrome, AIDS) or be multifactorial (e.g. cleft lip or palate, congenital heart disease).
• Acquired Conditions are caused by environmental factors after birth, such as trauma, infection, malnutrition, lack of oxygen.
22
Infectious Diseases
• Infection is the presence and multiplication of a living organism, virus or protein in or on a host organism.
• Note - not all microorganisms are detrimental to health (a normal microflora in the body is important for health).
• Agents of infectious disease (pathogens) include• prions (infectious proteins)*• viruses ( e.g. flu, cold, AIDS)• bacteria (e.g. salmonella – typhoid-TB)• rickettsiae (e.g. typhus)• chlamydiae (e.g. some STDs),• fungi (e.g. athletes foot)• animal parasites (e.g. Plasmodium, cause of malaria).
• Contagious (Communicable) Diseases are infectious diseases spread directly from person to person, e.g. measles (rubeola- a viral disease).
*Prions cause transmissible neurogenerative diseases, e.g. Creutzfeldt-Jacob disease
23
• Preclinical: not evident but destined to progress to clinical status - cantransmit infection to others, e.g. hepatitis B, HIV but may not show immune response yet.
• Clinical: shows signs and symptoms & positive test for antibodies.
•Sub-clinical: If a disease is inactive (dormant). Most cases of Tuberculosis- TB are “latent” TB: immune system is activated so person gives a positive immune response test result.
• A Carrier for an infectious communicable disease is an individual who harbours the pathogen and can infect others but may not show signs of the disease (e.g. preclinical Hepatitis B, HIV). Individuals with Latent TB cannot infect others so are not carriers.
Appearance of Infectious Diseases: Four States
Preclinical
Clinical Manifestation
of Disease
Clinical SubClinicalbecomes
No Clinical
Manifestation of Disease
carriermay act as
24
Clinical Manifestations of Disease - 1
Clinical Manifestations are various indications (signs and symptoms) that a patient is ill.
• Symptom: subjective complaint noticed only by the person with the disorder, e.g. feeling cold, tired, pain.
• Sign: manifestation noted or measured by medical observere.g. shivering, change in body temperature, swelling.Both may be related to the disorder or be indicators of the body’s compensatory mechanisms in action.
Disease is any disruption of normal structure or function of organ or system that is manifested by a characteristic set of signs and symptoms.
A Syndrome is a group of typical signs and symptoms associated with a disease enabling a diagnosis to be made.
25
Clinical Manifestations of Disease - 2
Signs
Syndrome
Symptoms
Clinical Manifestations of Disease
Disease
Diagnosis
Compensatory Homeostatic Responses
may cause
causes
causes
26
Diagnosis of Disease - 1
• Diagnosis is the designation of the nature of the disease.
- Involves careful consideration of history (symptoms) and physical examination (signs) .
- Requires determination of individual “normality” by taking into account age, sex, race, lifestyle, family history, etc.
- Often relies on information from epidemiology and pathogenesis.
• Diagnosis usually requires several pieces of information such as laboratory tests.
27
Diagnosis of Disease - Lab Tests
DiagnosisLaboratory Tests
•Reliable•Valid•Sensitive•Specific
- Reliable: test can be repeated with same result - Valid: test is a true measure of the disease- Sensitive: test gives no false -ves - delays treatment - Specific: test gives no false +ves - creates stress
must be
Positive
Negative
Present Absent
True
Positive
False
Negative
True
Negative
False
Positive
From Porth, fig 1-1
DISEASE
TESTRESULT
•Test Sensitivity gives %
of true +ves (persons
with disease).
•Test Specificity gives %
of true -ves (those with
no disease)
Pathogenesis: The Progression of Disease in Individuals
Pathogenesis is the development of a disease in a person, the sequence of cellular and tissue events following contact with etiological factorse.g. Inhalation of airborne bacteria from person with active TB causes cell mediated immune response that walls off infection in lungs.
•Pathogenesis involves studying morphological changes - seen in a biopsy, e.g. a lesion, using histology- seen with medical imaging e.g. X rays, CAT scans
e.g. TB nodules (granulomas) seen in lung X ray
•Pathogenesis describes how the disease process evolves and explains the clinical manifestations of the disease.
Diseases in individuals are studied in Pathology and Pathophysiology.
29
Clinical Course of Diseases
• Acute Disease is severe but self limiting, e.g. measles (rubeola).
• Chronic Disease is continuous long term e.g. malaria, TB.
Chronic Disease is persistent - sometimes for life, often characterized by flare ups (with exacerbation followed by remission).
Clinical Course is the pattern of development of a disease in an individual: it may be Acute or Chronic.
30
The Study of Disease in Populations
• Epidemiology was used originally to stop outbreaks of infectious disease during epidemics.
• Epidemiology is now used to study
- how disease spreads, how to control and eliminate it as well as- the risk factors for multifactorial diseases including
age, diet, race, lifestyle, location.
- the Natural History of Disease.
Epidemiology is the study of Disease in Populations
•The Natural History of Disease is its progression and projected outcome in general without intervention (e.g. 80% of persons with hepatitis C virus, for which there is no vaccine, tend to develop a chronic infection).
•Natural History provides data for preventative measures and prognosis.
•Prognosis is the probable outcome/ prospect of recovery in individuals and depends on epidemiological as well as personal data.
31
Morbidity Rates include• Incidence: % of new cases in a population at risk
in a specific time• Prevalence: % of people in population who have the disease at a given time
Epidemiology
Epidemiology measures disease frequency,
through the Incidence and Prevalence of disease in
populations using statistics
• Mortality (death) rates
• Morbidity (presence of disease & how disease affects person’s life over long term).